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25 .TH "JAVA" "1" "2019" "JDK 13" "JDK Commands"
26 .hy
27 .SH NAME
28 .PP
29 java \- launch a Java application
30 .SH SYNOPSIS
31 .PP
32 To launch a class file:
33 .PP
34 \f[CB]java\f[R] [\f[I]options\f[R]] \f[I]mainclass\f[R] [\f[I]args\f[R] ...]
35 .PP
36 To launch the main class in a JAR file:
37 .PP
38 \f[CB]java\f[R] [\f[I]options\f[R]] \f[CB]\-jar\f[R] \f[I]jarfile\f[R]
39 [\f[I]args\f[R] ...]
40 .PP
41 To launch the main class in a module:
42 .PP
43 \f[CB]java\f[R] [\f[I]options\f[R]] \f[CB]\-m\f[R]
44 \f[I]module\f[R][\f[CB]/\f[R]\f[I]mainclass\f[R]] [\f[I]args\f[R] ...]
45 .PP
46 or
47 .PP
48 \f[CB]java\f[R] [\f[I]options\f[R]] \f[CB]\-\-module\f[R]
49 \f[I]module\f[R][\f[CB]/\f[R]\f[I]mainclass\f[R]] [\f[I]args\f[R] ...]
50 .PP
51 To launch a single source\-file program:
52 .PP
53 \f[CB]java\f[R] [\f[I]options\f[R]] \f[I]source\-file\f[R] [\f[I]args\f[R]
54 \&...]
55 .TP
56 .B \f[I]options\f[R]
57 Optional: Specifies command\-line options separated by spaces.
58 See \f[B]Overview of Java Options\f[R] for a description of available
59 options.
60 .RS
61 .RE
62 .TP
63 .B \f[I]mainclass\f[R]
64 Specifies the name of the class to be launched.
65 Command\-line entries following \f[CB]classname\f[R] are the arguments for
66 the main method.
67 .RS
68 .RE
69 .TP
70 .B \f[CB]\-jar\f[R] \f[I]jarfile\f[R]
71 Executes a program encapsulated in a JAR file.
72 The \f[I]jarfile\f[R] argument is the name of a JAR file with a manifest
73 that contains a line in the form \f[CB]Main\-Class:\f[R]\f[I]classname\f[R]
74 that defines the class with the
75 \f[CB]public\ static\ void\ main(String[]\ args)\f[R] method that serves
76 as your application\[aq]s starting point.
77 When you use \f[CB]\-jar\f[R], the specified JAR file is the source of all
78 user classes, and other class path settings are ignored.
79 If you\[aq]re using JAR files, then see \f[B]jar\f[R].
80 .RS
81 .RE
82 .TP
83 .B \f[CB]\-m\f[R] or \f[CB]\-\-module\f[R] \f[I]module\f[R][\f[CB]/\f[R]\f[I]mainclass\f[R]]
84 Executes the main class in a module specified by \f[I]mainclass\f[R] if
85 it is given, or, if it is not given, the value in the \f[I]module\f[R].
86 In other words, \f[I]mainclass\f[R] can be used when it is not specified
87 by the module, or to override the value when it is specified.
88 .RS
89 .PP
90 See \f[B]Standard Options for Java\f[R].
91 .RE
92 .TP
93 .B \f[I]source\-file\f[R]
94 Only used to launch a single source\-file program.
95 Specifies the source file that contains the main class when using
96 source\-file mode.
97 See \f[B]Using Source\-File Mode to Launch Single\-File Source\-Code
98 Programs\f[R]
99 .RS
100 .RE
101 .TP
102 .B \f[I]args\f[R] ...
103 Optional: Arguments following \f[I]mainclass\f[R], \f[I]source\-file\f[R],
104 \f[CB]\-jar\f[R] \f[I]jarfile\f[R], and \f[CB]\-m\f[R] or \f[CB]\-\-module\f[R]
105 \f[I]module\f[R]\f[CB]/\f[R]\f[I]mainclass\f[R] are passed as arguments to
106 the main class.
107 .RS
108 .RE
109 .SH DESCRIPTION
110 .PP
111 The \f[CB]java\f[R] command starts a Java application.
112 It does this by starting the Java Virtual Machine (JVM), loading the
113 specified class, and calling that class\[aq]s \f[CB]main()\f[R] method.
114 The method must be declared \f[CB]public\f[R] and \f[CB]static\f[R], it must
115 not return any value, and it must accept a \f[CB]String\f[R] array as a
116 parameter.
117 The method declaration has the following form:
118 .RS
119 .PP
120 \f[CB]public\ static\ void\ main(String[]\ args)\f[R]
121 .RE
122 .PP
123 In source\-file mode, the \f[CB]java\f[R] command can launch a class
124 declared in a source file.
125 See \f[B]Using Source\-File Mode to Launch Single\-File Source\-Code
126 Programs\f[R] for a description of using the source\-file mode.
127 .RS
128 .PP
129 \f[B]Note:\f[R] You can use the \f[CB]JDK_JAVA_OPTIONS\f[R] launcher
130 environment variable to prepend its content to the actual command line
131 of the \f[CB]java\f[R] launcher.
132 See \f[B]Using the JDK_JAVA_OPTIONS Launcher Environment Variable\f[R].
133 .RE
134 .PP
135 By default, the first argument that isn\[aq]t an option of the
136 \f[CB]java\f[R] command is the fully qualified name of the class to be
137 called.
138 If \f[CB]\-jar\f[R] is specified, then its argument is the name of the JAR
139 file containing class and resource files for the application.
140 The startup class must be indicated by the \f[CB]Main\-Class\f[R] manifest
141 header in its manifest file.
142 .PP
143 Arguments after the class file name or the JAR file name are passed to
144 the \f[CB]main()\f[R] method.
145 .SS \f[CB]javaw\f[R]
146 .PP
147 \f[B]Windows:\f[R] The \f[CB]javaw\f[R] command is identical to
148 \f[CB]java\f[R], except that with \f[CB]javaw\f[R] there\[aq]s no associated
149 console window.
150 Use \f[CB]javaw\f[R] when you don\[aq]t want a command prompt window to
151 appear.
152 The \f[CB]javaw\f[R] launcher will, however, display a dialog box with
153 error information if a launch fails.
154 .SH USING SOURCE\-FILE MODE TO LAUNCH SINGLE\-FILE SOURCE\-CODE PROGRAMS
155 .PP
156 To launch a class declared in a source file, run the \f[CB]java\f[R]
157 launcher in source\-file mode.
158 Entering source\-file mode is determined by two items on the
159 \f[CB]java\f[R] command line:
160 .IP \[bu] 2
161 The first item on the command line that is not an option or part of an
162 option.
163 In other words, the item in the command line that would otherwise be the
164 main class name.
165 .IP \[bu] 2
166 The \f[CB]\-\-source\f[R] \f[I]version\f[R] option, if present.
167 .PP
168 If the class identifies an existing file that has a \f[CB]\&.java\f[R]
169 extension, or if the \f[CB]\-\-source\f[R] option is specified, then
170 source\-file mode is selected.
171 The source file is then compiled and run.
172 The \f[CB]\-\-source\f[R] option can be used to specify the source
173 \f[I]version\f[R] or \f[I]N\f[R] of the source code.
174 This determines the API that can be used.
175 When you set \f[CB]\-\-source\f[R] \f[I]N\f[R], you can only use the public
176 API that was defined in JDK \f[I]N\f[R].
177 .RS
178 .PP
179 \f[B]Note:\f[R] The valid values of \f[I]N\f[R] change for each release,
180 with new values added and old values removed.
181 You\[aq]ll get an error message if you use a value of \f[I]N\f[R] that is
182 no longer supported.
183 Supported values of \f[I]N\f[R] for this release are \f[CB]7\f[R],
184 \f[CB]8\f[R], \f[CB]9\f[R], \f[CB]10\f[R], \f[CB]11\f[R], \f[CB]12\f[R], and
185 \f[CB]13\f[R].
186 .RE
187 .PP
188 If the file does not have the \f[CB]\&.java\f[R] extension, the
189 \f[CB]\-\-source\f[R] option must be used to tell the \f[CB]java\f[R]
190 command to use the source\-file mode.
191 The \f[CB]\-\-source\f[R] option is used for cases when the source file is
192 a "script" to be executed and the name of the source file does not
193 follow the normal naming conventions for Java source files.
194 .PP
195 In source\-file mode, the effect is as though the source file is
196 compiled into memory, and the first class found in the source file is
197 executed.
198 Any arguments placed after the name of the source file in the original
199 command line are passed to the compiled class when it is executed.
200 .PP
201 For example, if a file were named \f[CB]HelloWorld.java\f[R] and contained
202 a class named \f[CB]hello.World\f[R], then the source\-file mode command
203 to launch the class would be:
204 .RS
205 .PP
206 \f[CB]java\ HelloWorld.java\f[R]
207 .RE
208 .PP
209 The example illustrates that the class can be in a named package, and
210 does not need to be in the unnamed package.
211 This use of source\-file mode is informally equivalent to using the
212 following two commands where \f[CB]hello.World\f[R] is the name of the
213 class in the package:
214 .IP
215 .nf
216 \f[CB]
217 javac\ \-d\ <memory>\ HelloWorld.java
218 java\ \-cp\ <memory>\ hello.World
219 \f[R]
220 .fi
221 .PP
222 \f[B]In source\-file mode, any additional command\-line options are
223 processed as follows:\f[R]
224 .IP \[bu] 2
225 The launcher scans the options specified before the source file for any
226 that are relevant in order to compile the source file.
227 .RS 2
228 .PP
229 This includes: \f[CB]\-\-class\-path\f[R], \f[CB]\-\-module\-path\f[R],
230 \f[CB]\-\-add\-exports\f[R], \f[CB]\-\-add\-modules\f[R],
231 \f[CB]\-\-limit\-modules\f[R], \f[CB]\-\-patch\-module\f[R],
232 \f[CB]\-\-upgrade\-module\-path\f[R], and any variant forms of those
233 options.
234 It also includes the new \f[CB]\-\-enable\-preview\f[R] option, described
235 in JEP 12.
236 .RE
237 .IP \[bu] 2
238 No provision is made to pass any additional options to the compiler,
239 such as \f[CB]\-processor\f[R] or \f[CB]\-Werror\f[R].
240 .IP \[bu] 2
241 Command\-line argument files (\f[CB]\@\f[R]\-files) may be used in the
242 standard way.
243 Long lists of arguments for either the VM or the program being invoked
244 may be placed in files specified on the command\-line by prefixing the
245 filename with an \f[CB]\@\f[R] character.
246 .PP
247 \f[B]In source\-file mode, compilation proceeds as follows:\f[R]
248 .IP \[bu] 2
249 Any command\-line options that are relevant to the compilation
250 environment are taken into account.
251 .IP \[bu] 2
252 No other source files are found and compiled, as if the source path is
253 set to an empty value.
254 .IP \[bu] 2
255 Annotation processing is disabled, as if \f[CB]\-proc:none\f[R] is in
256 effect.
257 .IP \[bu] 2
258 If a version is specified, via the \f[CB]\-\-source\f[R] option, the value
259 is used as the argument for an implicit \f[CB]\-\-release\f[R] option for
260 the compilation.
261 This sets both the source version accepted by compiler and the system
262 API that may be used by the code in the source file.
263 .IP \[bu] 2
264 The source file is compiled in the context of an unnamed module.
265 .IP \[bu] 2
266 The source file should contain one or more top\-level classes, the first
267 of which is taken as the class to be executed.
268 .IP \[bu] 2
269 The compiler does not enforce the optional restriction defined at the
270 end of JLS §7.6, that a type in a named package should exist in a file
271 whose name is composed from the type name followed by the
272 \f[CB]\&.java\f[R] extension.
273 .IP \[bu] 2
274 If the source file contains errors, appropriate error messages are
275 written to the standard error stream, and the launcher exits with a
276 non\-zero exit code.
277 .PP
278 \f[B]In source\-file mode, execution proceeds as follows:\f[R]
279 .IP \[bu] 2
280 The class to be executed is the first top\-level class found in the
281 source file.
282 It must contain a declaration of the standard
283 \f[CB]public\ static\ void\ main(String[])\f[R] method.
284 .IP \[bu] 2
285 The compiled classes are loaded by a custom class loader, that delegates
286 to the application class loader.
287 This implies that classes appearing on the application class path cannot
288 refer to any classes declared in the source file.
289 .IP \[bu] 2
290 The compiled classes are executed in the context of an unnamed module,
291 as though \f[CB]\-\-add\-modules=ALL\-DEFAULT\f[R] is in effect.
292 This is in addition to any other \f[CB]\-\-add\-module\f[R] options that
293 may be have been specified on the command line.
294 .IP \[bu] 2
295 Any arguments appearing after the name of the file on the command line
296 are passed to the standard main method in the obvious way.
297 .IP \[bu] 2
298 It is an error if there is a class on the application class path whose
299 name is the same as that of the class to be executed.
300 .PP
301 See \f[B]JEP 330: Launch Single\-File Source\-Code Programs\f[R]
302 [http://openjdk.java.net/jeps/330] for complete details.
303 .SH USING THE JDK_JAVA_OPTIONS LAUNCHER ENVIRONMENT VARIABLE
304 .PP
305 \f[CB]JDK_JAVA_OPTIONS\f[R] prepends its content to the options parsed
306 from the command line.
307 The content of the \f[CB]JDK_JAVA_OPTIONS\f[R] environment variable is a
308 list of arguments separated by white\-space characters (as determined by
309 \f[CB]isspace()\f[R]).
310 These are prepended to the command line arguments passed to
311 \f[CB]java\f[R] launcher.
312 The encoding requirement for the environment variable is the same as the
313 \f[CB]java\f[R] command line on the system.
314 \f[CB]JDK_JAVA_OPTIONS\f[R] environment variable content is treated in the
315 same manner as that specified in the command line.
316 .PP
317 Single (\f[CB]\[aq]\f[R]) or double (\f[CB]"\f[R]) quotes can be used to
318 enclose arguments that\ contain whitespace characters.
319 All content between the open quote and the first matching close quote
320 are preserved by simply removing the pair of quotes.
321 In case a matching quote is not found, the launcher will abort with an
322 error message.
323 \f[CB]\@\f[R]\-files are supported as they are specified in the command
324 line.
325 However, as in \f[CB]\@\f[R]\-files, use of a wildcard is not supported.
326 In order to mitigate potential misuse of \f[CB]JDK_JAVA_OPTIONS\f[R]
327 behavior, options that specify the main class (such as \f[CB]\-jar\f[R])
328 or cause the \f[CB]java\f[R] launcher to exit without executing the main
329 class (such as \f[CB]\-h\f[R]) are disallowed in the environment variable.
330 If any of these options appear in the environment variable, the launcher
331 will abort with an error message.
332 When \f[CB]JDK_JAVA_OPTIONS\f[R] is set, the launcher prints a message to
333 stderr as a reminder.
334 .PP
335 \f[B]Example:\f[R]
336 .IP
337 .nf
338 \f[CB]
339 $\ export\ JDK_JAVA_OPTIONS=\[aq]\-g\ \@file1\ \-Dprop=value\ \@file2\ \-Dws.prop="white\ spaces"\[aq]
340 $\ java\ \-Xint\ \@file3
341 \f[R]
342 .fi
343 .PP
344 is equivalent to the command line:
345 .IP
346 .nf
347 \f[CB]
348 java\ \-g\ \@file1\ \-Dprop=value\ \@file2\ \-Dws.prop="white\ spaces"\ \-Xint\ \@file3
349 \f[R]
350 .fi
351 .SH OVERVIEW OF JAVA OPTIONS
352 .PP
353 The \f[CB]java\f[R] command supports a wide range of options in the
354 following categories:
355 .IP \[bu] 2
356 \f[B]Standard Options for Java\f[R]: Options guaranteed to be supported
357 by all implementations of the Java Virtual Machine (JVM).
358 They\[aq]re used for common actions, such as checking the version of the
359 JRE, setting the class path, enabling verbose output, and so on.
360 .IP \[bu] 2
361 \f[B]Extra Options for Java\f[R]: General purpose options that are
362 specific to the Java HotSpot Virtual Machine.
363 They aren\[aq]t guaranteed to be supported by all JVM implementations,
364 and are subject to change.
365 These options start with \f[CB]\-X\f[R].
366 .PP
367 The advanced options aren\[aq]t recommended for casual use.
368 These are developer options used for tuning specific areas of the Java
369 HotSpot Virtual Machine operation that often have specific system
370 requirements and may require privileged access to system configuration
371 parameters.
372 Several examples of performance tuning are provided in \f[B]Performance
373 Tuning Examples\f[R].
374 These options aren\[aq]t guaranteed to be supported by all JVM
375 implementations and are subject to change.
376 Advanced options start with \f[CB]\-XX\f[R].
377 .IP \[bu] 2
378 \f[B]Advanced Runtime Options for Java\f[R]: Control the runtime behavior
379 of the Java HotSpot VM.
380 .IP \[bu] 2
381 \f[B]Advanced JIT Compiler Options for java\f[R]: Control the dynamic
382 just\-in\-time (JIT) compilation performed by the Java HotSpot VM.
383 .IP \[bu] 2
384 \f[B]Advanced Serviceability Options for Java\f[R]: Enable gathering
385 system information and performing extensive debugging.
386 .IP \[bu] 2
387 \f[B]Advanced Garbage Collection Options for Java\f[R]: Control how
388 garbage collection (GC) is performed by the Java HotSpot
389 .PP
390 Boolean options are used to either enable a feature that\[aq]s disabled
391 by default or disable a feature that\[aq]s enabled by default.
392 Such options don\[aq]t require a parameter.
393 Boolean \f[CB]\-XX\f[R] options are enabled using the plus sign
394 (\f[CB]\-XX:+\f[R]\f[I]OptionName\f[R]) and disabled using the minus sign
395 (\f[CB]\-XX:\-\f[R]\f[I]OptionName\f[R]).
396 .PP
397 For options that require an argument, the argument may be separated from
398 the option name by a space, a colon (:), or an equal sign (=), or the
399 argument may directly follow the option (the exact syntax differs for
400 each option).
401 If you\[aq]re expected to specify the size in bytes, then you can use no
402 suffix, or use the suffix \f[CB]k\f[R] or \f[CB]K\f[R] for kilobytes (KB),
403 \f[CB]m\f[R] or \f[CB]M\f[R] for megabytes (MB), or \f[CB]g\f[R] or \f[CB]G\f[R]
404 for gigabytes (GB).
405 For example, to set the size to 8 GB, you can specify either
406 \f[CB]8g\f[R], \f[CB]8192m\f[R], \f[CB]8388608k\f[R], or \f[CB]8589934592\f[R]
407 as the argument.
408 If you are expected to specify the percentage, then use a number from 0
409 to 1.
410 For example, specify \f[CB]0.25\f[R] for 25%.
411 .PP
412 The following sections describe the options that are obsolete,
413 deprecated, and removed:
414 .IP \[bu] 2
415 \f[B]Deprecated Java Options\f[R]: Accepted and acted upon \-\-\- a
416 warning is issued when they\[aq]re used.
417 .IP \[bu] 2
418 \f[B]Obsolete Java Options\f[R]: Accepted but ignored \-\-\- a warning is
419 issued when they\[aq]re used.
420 .IP \[bu] 2
421 \f[B]Removed Java Options\f[R]: Removed \-\-\- using them results in an
422 error.
423 .SH STANDARD OPTIONS FOR JAVA
424 .PP
425 These are the most commonly used options supported by all
426 implementations of the JVM.
427 .RS
428 .PP
429 \f[B]Note:\f[R] To specify an argument for a long option, you can use
430 either \f[CB]\-\-\f[R]\f[I]name\f[R]\f[CB]=\f[R]\f[I]value\f[R] or
431 \f[CB]\-\-\f[R]\f[I]name\f[R] \f[I]value\f[R].
432 .RE
433 .TP
434 .B \f[CB]\-agentlib:\f[R]\f[I]libname\f[R][\f[CB]=\f[R]\f[I]options\f[R]]
435 Loads the specified native agent library.
436 After the library name, a comma\-separated list of options specific to
437 the library can be used.
438 .RS
439 .IP \[bu] 2
440 \f[B]Oracle Solaris, Linux, and macOS:\f[R] If the option
441 \f[CB]\-agentlib:foo\f[R] is specified, then the JVM attempts to load the
442 library named \f[CB]libfoo.so\f[R] in the location specified by the
443 \f[CB]LD_LIBRARY_PATH\f[R] system variable (on macOS this variable is
444 \f[CB]DYLD_LIBRARY_PATH\f[R]).
445 .IP \[bu] 2
446 \f[B]Windows:\f[R] If the option \f[CB]\-agentlib:foo\f[R] is specified,
447 then the JVM attempts to load the library named \f[CB]foo.dll\f[R] in the
448 location specified by the \f[CB]PATH\f[R] system variable.
449 .RS 2
450 .PP
451 The following example shows how to load the Java Debug Wire Protocol
452 (JDWP) library and listen for the socket connection on port 8000,
453 suspending the JVM before the main class loads:
454 .RS
455 .PP
456 \f[CB]\-agentlib:jdwp=transport=dt_socket,server=y,address=8000\f[R]
457 .RE
458 .RE
459 .RE
460 .TP
461 .B \f[CB]\-agentpath:\f[R]\f[I]pathname\f[R][\f[CB]=\f[R]\f[I]options\f[R]]
462 Loads the native agent library specified by the absolute path name.
463 This option is equivalent to \f[CB]\-agentlib\f[R] but uses the full path
464 and file name of the library.
465 .RS
466 .RE
467 .TP
468 .B \f[CB]\-\-class\-path\f[R] \f[I]classpath\f[R], \f[CB]\-classpath\f[R] \f[I]classpath\f[R], or \f[CB]\-cp\f[R] \f[I]classpath\f[R]
469 A semicolon (\f[CB];\f[R]) separated list of directories, JAR archives,
470 and ZIP archives to search for class files.
471 .RS
472 .PP
473 Specifying \f[I]classpath\f[R] overrides any setting of the
474 \f[CB]CLASSPATH\f[R] environment variable.
475 If the class path option isn\[aq]t used and \f[I]classpath\f[R] isn\[aq]t
476 set, then the user class path consists of the current directory (.).
477 .PP
478 As a special convenience, a class path element that contains a base name
479 of an asterisk (*) is considered equivalent to specifying a list of all
480 the files in the directory with the extension \f[CB]\&.jar\f[R] or
481 \f[CB]\&.JAR\f[R] .
482 A Java program can\[aq]t tell the difference between the two
483 invocations.
484 For example, if the directory mydir contains \f[CB]a.jar\f[R] and
485 \f[CB]b.JAR\f[R], then the class path element mydir/* is expanded to
486 \f[CB]A.jar:b.JAR\f[R], except that the order of JAR files is unspecified.
487 All \f[CB]\&.jar\f[R] files in the specified directory, even hidden ones,
488 are included in the list.
489 A class path entry consisting of an asterisk (*) expands to a list of
490 all the jar files in the current directory.
491 The \f[CB]CLASSPATH\f[R] environment variable, where defined, is similarly
492 expanded.
493 Any class path wildcard expansion that occurs before the Java VM is
494 started.
495 Java programs never see wildcards that aren\[aq]t expanded except by
496 querying the environment, such as by calling
497 \f[CB]System.getenv("CLASSPATH")\f[R].
498 .RE
499 .TP
500 .B \f[CB]\-\-disable\-\@files\f[R]
501 Can be used anywhere on the command line, including in an argument file,
502 to prevent further \f[CB]\@filename\f[R] expansion.
503 This option stops expanding \f[CB]\@\f[R]\-argfiles after the option.
504 .RS
505 .RE
506 .TP
507 .B \f[CB]\-\-enable\-preview\f[R]
508 Allows classes to depend on \f[B]preview features\f[R]
509 [https://docs.oracle.com/en/java/javase/12/language/index.html#JSLAN\-GUID\-5A82FE0E\-0CA4\-4F1F\-B075\-564874FE2823]
510 of the release.
511 .RS
512 .RE
513 .TP
514 .B \f[CB]\-\-module\-path\f[R] \f[I]modulepath\f[R]... or \f[CB]\-p\f[R] \f[I]modulepath\f[R]
515 A semicolon (\f[CB];\f[R]) separated list of directories in which each
516 directory is a directory of modules.
517 .RS
518 .RE
519 .TP
520 .B \f[CB]\-\-upgrade\-module\-path\f[R] \f[I]modulepath\f[R]...
521 A semicolon (\f[CB];\f[R]) separated list of directories in which each
522 directory is a directory of modules that replace upgradeable modules in
523 the runtime image.
524 .RS
525 .RE
526 .TP
527 .B \f[CB]\-\-add\-modules\f[R] \f[I]module\f[R][\f[CB],\f[R]\f[I]module\f[R]...]
528 Specifies the root modules to resolve in addition to the initial module.
529 \f[I]module\f[R] also can be \f[CB]ALL\-DEFAULT\f[R], \f[CB]ALL\-SYSTEM\f[R],
530 and \f[CB]ALL\-MODULE\-PATH\f[R].
531 .RS
532 .RE
533 .TP
534 .B \f[CB]\-\-list\-modules\f[R]
535 Lists the observable modules and then exits.
536 .RS
537 .RE
538 .TP
539 .B \f[CB]\-d\f[R] \f[I]module_name\f[R] or \f[CB]\-\-describe\-module\f[R] \f[I]module_name\f[R]
540 Describes a specified module and then exits.
541 .RS
542 .RE
543 .TP
544 .B \f[CB]\-\-dry\-run\f[R]
545 Creates the VM but doesn\[aq]t execute the main method.
546 This \f[CB]\-\-dry\-run\f[R] option might be useful for validating the
547 command\-line options such as the module system configuration.
548 .RS
549 .RE
550 .TP
551 .B \f[CB]\-\-validate\-modules\f[R]
552 Validates all modules and exit.
553 This option is helpful for finding conflicts and other errors with
554 modules on the module path.
555 .RS
556 .RE
557 .TP
558 .B \f[CB]\-D\f[R]\f[I]property\f[R]\f[CB]=\f[R]\f[I]value\f[R]
559 Sets a system property value.
560 The \f[I]property\f[R] variable is a string with no spaces that
561 represents the name of the property.
562 The \f[I]value\f[R] variable is a string that represents the value of the
563 property.
564 If \f[I]value\f[R] is a string with spaces, then enclose it in quotation
565 marks (for example \f[CB]\-Dfoo="foo\ bar"\f[R]).
566 .RS
567 .RE
568 .TP
569 .B \f[CB]\-disableassertions\f[R][\f[CB]:\f[R][\f[I]packagename\f[R]]...|\f[CB]:\f[R]\f[I]classname\f[R]] or \f[CB]\-da\f[R][\f[CB]:\f[R][\f[I]packagename\f[R]]...|\f[CB]:\f[R]\f[I]classname\f[R]]
570 Disables assertions.
571 By default, assertions are disabled in all packages and classes.
572 With no arguments, \f[CB]\-disableassertions\f[R] (\f[CB]\-da\f[R]) disables
573 assertions in all packages and classes.
574 With the \f[I]packagename\f[R] argument ending in \f[CB]\&...\f[R], the
575 switch disables assertions in the specified package and any subpackages.
576 If the argument is simply \f[CB]\&...\f[R], then the switch disables
577 assertions in the unnamed package in the current working directory.
578 With the \f[I]classname\f[R] argument, the switch disables assertions in
579 the specified class.
580 .RS
581 .PP
582 The \f[CB]\-disableassertions\f[R] (\f[CB]\-da\f[R]) option applies to all
583 class loaders and to system classes (which don\[aq]t have a class
584 loader).
585 There\[aq]s one exception to this rule: If the option is provided with
586 no arguments, then it doesn\[aq]t apply to system classes.
587 This makes it easy to disable assertions in all classes except for
588 system classes.
589 The \f[CB]\-disablesystemassertions\f[R] option enables you to disable
590 assertions in all system classes.
591 To explicitly enable assertions in specific packages or classes, use the
592 \f[CB]\-enableassertions\f[R] (\f[CB]\-ea\f[R]) option.
593 Both options can be used at the same time.
594 For example, to run the \f[CB]MyClass\f[R] application with assertions
595 enabled in the package \f[CB]com.wombat.fruitbat\f[R] (and any
596 subpackages) but disabled in the class
597 \f[CB]com.wombat.fruitbat.Brickbat\f[R], use the following command:
598 .RS
599 .PP
600 \f[CB]java\ \-ea:com.wombat.fruitbat...\ \-da:com.wombat.fruitbat.Brickbat\ MyClass\f[R]
601 .RE
602 .RE
603 .TP
604 .B \f[CB]\-disablesystemassertions\f[R] or \f[CB]\-dsa\f[R]
605 Disables assertions in all system classes.
606 .RS
607 .RE
608 .TP
609 .B \f[CB]\-enableassertions\f[R][\f[CB]:\f[R][\f[I]packagename\f[R]]...|\f[CB]:\f[R]\f[I]classname\f[R]] or \f[CB]\-ea\f[R][\f[CB]:\f[R][\f[I]packagename\f[R]]...|\f[CB]:\f[R]\f[I]classname\f[R]]
610 Enables assertions.
611 By default, assertions are disabled in all packages and classes.
612 With no arguments, \f[CB]\-enableassertions\f[R] (\f[CB]\-ea\f[R]) enables
613 assertions in all packages and classes.
614 With the \f[I]packagename\f[R] argument ending in \f[CB]\&...\f[R], the
615 switch enables assertions in the specified package and any subpackages.
616 If the argument is simply \f[CB]\&...\f[R], then the switch enables
617 assertions in the unnamed package in the current working directory.
618 With the \f[I]classname\f[R] argument, the switch enables assertions in
619 the specified class.
620 .RS
621 .PP
622 The \f[CB]\-enableassertions\f[R] (\f[CB]\-ea\f[R]) option applies to all
623 class loaders and to system classes (which don\[aq]t have a class
624 loader).
625 There\[aq]s one exception to this rule: If the option is provided with
626 no arguments, then it doesn\[aq]t apply to system classes.
627 This makes it easy to enable assertions in all classes except for system
628 classes.
629 The \f[CB]\-enablesystemassertions\f[R] option provides a separate switch
630 to enable assertions in all system classes.
631 To explicitly disable assertions in specific packages or classes, use
632 the \f[CB]\-disableassertions\f[R] (\f[CB]\-da\f[R]) option.
633 If a single command contains multiple instances of these switches, then
634 they\[aq]re processed in order, before loading any classes.
635 For example, to run the \f[CB]MyClass\f[R] application with assertions
636 enabled only in the package \f[CB]com.wombat.fruitbat\f[R] (and any
637 subpackages) but disabled in the class
638 \f[CB]com.wombat.fruitbat.Brickbat\f[R], use the following command:
639 .RS
640 .PP
641 \f[CB]java\ \-ea:com.wombat.fruitbat...\ \-da:com.wombat.fruitbat.Brickbat\ MyClass\f[R]
642 .RE
643 .RE
644 .TP
645 .B \f[CB]\-enablesystemassertions\f[R] or \f[CB]\-esa\f[R]
646 Enables assertions in all system classes.
647 .RS
648 .RE
649 .TP
650 .B \f[CB]\-help\f[R], \f[CB]\-h\f[R], or \f[CB]\-?\f[R]
651 Prints the help message to the error stream.
652 .RS
653 .RE
654 .TP
655 .B \f[CB]\-\-help\f[R]
656 Prints the help message to the output stream.
657 .RS
658 .RE
659 .TP
660 .B \f[CB]\-javaagent:\f[R]\f[I]jarpath\f[R][\f[CB]=\f[R]\f[I]options\f[R]]
661 Loads the specified Java programming language agent.
662 See \f[CB]java.lang.instrument\f[R].
663 .RS
664 .RE
665 .TP
666 .B \f[CB]\-\-show\-version\f[R]
667 Prints the product version to the output stream and continues.
668 .RS
669 .RE
670 .TP
671 .B \f[CB]\-showversion\f[R]
672 Prints the product version to the error stream and continues.
673 .RS
674 .RE
675 .TP
676 .B \f[CB]\-\-show\-module\-resolution\f[R]
677 Shows module resolution output during startup.
678 .RS
679 .RE
680 .TP
681 .B \f[CB]\-splash:\f[R]\f[I]imagepath\f[R]
682 Shows the splash screen with the image specified by \f[I]imagepath\f[R].
683 HiDPI scaled images are automatically supported and used if available.
684 The unscaled image file name, such as \f[CB]image.ext\f[R], should always
685 be passed as the argument to the \f[CB]\-splash\f[R] option.
686 The most appropriate scaled image provided is picked up automatically.
687 .RS
688 .PP
689 For example, to show the \f[CB]splash.gif\f[R] file from the
690 \f[CB]images\f[R] directory when starting your application, use the
691 following option:
692 .RS
693 .PP
694 \f[CB]\-splash:images/splash.gif\f[R]
695 .RE
696 .PP
697 See the SplashScreen API documentation for more information.
698 .RE
699 .TP
700 .B \f[CB]\-verbose:class\f[R]
701 Displays information about each loaded class.
702 .RS
703 .RE
704 .TP
705 .B \f[CB]\-verbose:gc\f[R]
706 Displays information about each garbage collection (GC) event.
707 .RS
708 .RE
709 .TP
710 .B \f[CB]\-verbose:jni\f[R]
711 Displays information about the use of native methods and other Java
712 Native Interface (JNI) activity.
713 .RS
714 .RE
715 .TP
716 .B \f[CB]\-verbose:module\f[R]
717 Displays information about the modules in use.
718 .RS
719 .RE
720 .TP
721 .B \f[CB]\-\-version\f[R]
722 Prints product version to the output stream and exits.
723 .RS
724 .RE
725 .TP
726 .B \f[CB]\-version\f[R]
727 Prints product version to the error stream and exits.
728 .RS
729 .RE
730 .TP
731 .B \f[CB]\-X\f[R]
732 Prints the help on extra options to the error stream.
733 .RS
734 .RE
735 .TP
736 .B \f[CB]\-\-help\-extra\f[R]
737 Prints the help on extra options to the output stream.
738 .RS
739 .RE
740 .TP
741 .B \f[CB]\@\f[R]\f[I]argfile\f[R]
742 Specifies one or more argument files prefixed by \f[CB]\@\f[R] used by the
743 \f[CB]java\f[R] command.
744 It isn\[aq]t uncommon for the \f[CB]java\f[R] command line to be very long
745 because of the \f[CB]\&.jar\f[R] files needed in the classpath.
746 The \f[CB]\@\f[R]\f[I]argfile\f[R] option overcomes command\-line length
747 limitations by enabling the launcher to expand the contents of argument
748 files after shell expansion, but before argument processing.
749 Contents in the argument files are expanded because otherwise, they
750 would be specified on the command line until the
751 \f[CB]\-\-disable\-\@files\f[R] option was encountered.
752 .RS
753 .PP
754 The argument files can also contain the main class name and all options.
755 If an argument file contains all of the options required by the
756 \f[CB]java\f[R] command, then the command line could simply be:
757 .RS
758 .PP
759 \f[CB]java\ \@\f[R]\f[I]argfile\f[R]
760 .RE
761 .PP
762 See \f[B]java Command\-Line Argument Files\f[R] for a description and
763 examples of using \f[CB]\@\f[R]\-argfiles.
764 .RE
765 .SH EXTRA OPTIONS FOR JAVA
766 .PP
767 The following \f[CB]java\f[R] options are general purpose options that are
768 specific to the Java HotSpot Virtual Machine.
769 .TP
770 .B \f[CB]\-Xbatch\f[R]
771 Disables background compilation.
772 By default, the JVM compiles the method as a background task, running
773 the method in interpreter mode until the background compilation is
774 finished.
775 The \f[CB]\-Xbatch\f[R] flag disables background compilation so that
776 compilation of all methods proceeds as a foreground task until
777 completed.
778 This option is equivalent to \f[CB]\-XX:\-BackgroundCompilation\f[R].
779 .RS
780 .RE
781 .TP
782 .B \f[CB]\-Xbootclasspath/a:\f[R]\f[I]directories\f[R]|\f[I]zip\f[R]|\f[I]JAR\-files\f[R]
783 Specifies a list of directories, JAR files, and ZIP archives to append
784 to the end of the default bootstrap class path.
785 .RS
786 .PP
787 \f[B]Oracle Solaris, Linux, and macOS:\f[R] Colons (\f[CB]:\f[R]) separate
788 entities in this list.
789 .PP
790 \f[B]Windows:\f[R] Semicolons (\f[CB];\f[R]) separate entities in this
791 list.
792 .RE
793 .TP
794 .B \f[CB]\-Xcheck:jni\f[R]
795 Performs additional checks for Java Native Interface (JNI) functions.
796 Specifically, it validates the parameters passed to the JNI function and
797 the runtime environment data before processing the JNI request.
798 It also checks for pending exceptions between JNI calls.
799 Any invalid data encountered indicates a problem in the native code, and
800 the JVM terminates with an irrecoverable error in such cases.
801 Expect a performance degradation when this option is used.
802 .RS
803 .RE
804 .TP
805 .B \f[CB]\-Xcomp\f[R]
806 Forces compilation of methods on first invocation.
807 By default, the Client VM (\f[CB]\-client\f[R]) performs 1,000 interpreted
808 method invocations and the Server VM (\f[CB]\-server\f[R]) performs 10,000
809 interpreted method invocations to gather information for efficient
810 compilation.
811 Specifying the \f[CB]\-Xcomp\f[R] option disables interpreted method
812 invocations to increase compilation performance at the expense of
813 efficiency.
814 You can also change the number of interpreted method invocations before
815 compilation using the \f[CB]\-XX:CompileThreshold\f[R] option.
816 .RS
817 .RE
818 .TP
819 .B \f[CB]\-Xdebug\f[R]
820 Does nothing.
821 Provided for backward compatibility.
822 .RS
823 .RE
824 .TP
825 .B \f[CB]\-Xdiag\f[R]
826 Shows additional diagnostic messages.
827 .RS
828 .RE
829 .TP
830 .B \f[CB]\-Xint\f[R]
831 Runs the application in interpreted\-only mode.
832 Compilation to native code is disabled, and all bytecode is executed by
833 the interpreter.
834 The performance benefits offered by the just\-in\-time (JIT) compiler
835 aren\[aq]t present in this mode.
836 .RS
837 .RE
838 .TP
839 .B \f[CB]\-Xinternalversion\f[R]
840 Displays more detailed JVM version information than the
841 \f[CB]\-version\f[R] option, and then exits.
842 .RS
843 .RE
844 .TP
845 .B \f[CB]\-Xlog:\f[R]\f[I]option\f[R]
846 Configure or enable logging with the Java Virtual Machine (JVM) unified
847 logging framework.
848 See \f[B]Enable Logging with the JVM Unified Logging Framework\f[R].
849 .RS
850 .RE
851 .TP
852 .B \f[CB]\-Xmixed\f[R]
853 Executes all bytecode by the interpreter except for hot methods, which
854 are compiled to native code.
855 .RS
856 .RE
857 .TP
858 .B \f[CB]\-Xmn\f[R] \f[I]size\f[R]
859 Sets the initial and maximum size (in bytes) of the heap for the young
860 generation (nursery) in the generational collectors.
861 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
862 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
863 \f[CB]G\f[R] to indicate gigabytes.
864 The young generation region of the heap is used for new objects.
865 GC is performed in this region more often than in other regions.
866 If the size for the young generation is too small, then a lot of minor
867 garbage collections are performed.
868 If the size is too large, then only full garbage collections are
869 performed, which can take a long time to complete.
870 It is recommended that you do not set the size for the young generation
871 for the G1 collector, and keep the size for the young generation greater
872 than 25% and less than 50% of the overall heap size for other
873 collectors.
874 The following examples show how to set the initial and maximum size of
875 young generation to 256 MB using various units:
876 .RS
877 .IP
878 .nf
879 \f[CB]
880 \-Xmn256m
881 \-Xmn262144k
882 \-Xmn268435456
883 \f[R]
884 .fi
885 .PP
886 Instead of the \f[CB]\-Xmn\f[R] option to set both the initial and maximum
887 size of the heap for the young generation, you can use
888 \f[CB]\-XX:NewSize\f[R] to set the initial size and
889 \f[CB]\-XX:MaxNewSize\f[R] to set the maximum size.
890 .RE
891 .TP
892 .B \f[CB]\-Xms\f[R] \f[I]size\f[R]
893 Sets the minimum and initial size (in bytes) of the heap.
894 This value must be a multiple of 1024 and greater than 1 MB.
895 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
896 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, \f[CB]g\f[R] or \f[CB]G\f[R]
897 to indicate gigabytes.
898 The following examples show how to set the size of allocated memory to 6
899 MB using various units:
900 .RS
901 .IP
902 .nf
903 \f[CB]
904 \-Xms6291456
905 \-Xms6144k
906 \-Xms6m
907 \f[R]
908 .fi
909 .PP
910 Instead of the \f[CB]\-Xms\f[R] option to set both the minimum and initial
911 size of the heap, you can use \f[CB]\-XX:MinHeapSize\f[R] to set the
912 minimum size and \f[CB]\-XX:InitialHeapSize\f[R] to set the initial size.
913 .PP
914 If you don\[aq]t set this option, the initial size is set as the sum of
915 the sizes allocated for the old generation and the young generation.
916 The initial size of the heap for the young generation can be set using
917 the \f[CB]\-Xmn\f[R] option or the \f[CB]\-XX:NewSize\f[R] option.
918 .RE
919 .TP
920 .B \f[CB]\-Xmx\f[R] \f[I]size\f[R]
921 Specifies the maximum size (in bytes) of the heap.
922 This value must be a multiple of 1024 and greater than 2 MB.
923 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
924 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
925 \f[CB]G\f[R] to indicate gigabytes.
926 The default value is chosen at runtime based on system configuration.
927 For server deployments, \f[CB]\-Xms\f[R] and \f[CB]\-Xmx\f[R] are often set
928 to the same value.
929 The following examples show how to set the maximum allowed size of
930 allocated memory to 80 MB using various units:
931 .RS
932 .IP
933 .nf
934 \f[CB]
935 \-Xmx83886080
936 \-Xmx81920k
937 \-Xmx80m
938 \f[R]
939 .fi
940 .PP
941 The \f[CB]\-Xmx\f[R] option is equivalent to \f[CB]\-XX:MaxHeapSize\f[R].
942 .RE
943 .TP
944 .B \f[CB]\-Xnoclassgc\f[R]
945 Disables garbage collection (GC) of classes.
946 This can save some GC time, which shortens interruptions during the
947 application run.
948 When you specify \f[CB]\-Xnoclassgc\f[R] at startup, the class objects in
949 the application are left untouched during GC and are always be
950 considered live.
951 This can result in more memory being permanently occupied which, if not
952 used carefully, throws an out\-of\-memory exception.
953 .RS
954 .RE
955 .TP
956 .B \f[CB]\-Xrs\f[R]
957 Reduces the use of operating system signals by the JVM.
958 Shutdown hooks enable the orderly shutdown of a Java application by
959 running user cleanup code (such as closing database connections) at
960 shutdown, even if the JVM terminates abruptly.
961 .RS
962 .IP \[bu] 2
963 \f[B]Oracle Solaris, Linux, and macOS:\f[R]
964 .RS 2
965 .IP \[bu] 2
966 The JVM catches signals to implement shutdown hooks for unexpected
967 termination.
968 The JVM uses \f[CB]SIGHUP\f[R], \f[CB]SIGINT\f[R], and \f[CB]SIGTERM\f[R] to
969 initiate the running of shutdown hooks.
970 .IP \[bu] 2
971 Applications embedding the JVM frequently need to trap signals such as
972 \f[CB]SIGINT\f[R] or \f[CB]SIGTERM\f[R], which can lead to interference with
973 the JVM signal handlers.
974 The \f[CB]\-Xrs\f[R] option is available to address this issue.
975 When \f[CB]\-Xrs\f[R] is used, the signal masks for \f[CB]SIGINT\f[R],
976 \f[CB]SIGTERM\f[R], \f[CB]SIGHUP\f[R], and \f[CB]SIGQUIT\f[R] aren\[aq]t
977 changed by the JVM, and signal handlers for these signals aren\[aq]t
978 installed.
979 .RE
980 .IP \[bu] 2
981 \f[B]Windows:\f[R]
982 .RS 2
983 .IP \[bu] 2
984 The JVM watches for console control events to implement shutdown hooks
985 for unexpected termination.
986 Specifically, the JVM registers a console control handler that begins
987 shutdown\-hook processing and returns \f[CB]TRUE\f[R] for
988 \f[CB]CTRL_C_EVENT\f[R], \f[CB]CTRL_CLOSE_EVENT\f[R],
989 \f[CB]CTRL_LOGOFF_EVENT\f[R], and \f[CB]CTRL_SHUTDOWN_EVENT\f[R].
990 .IP \[bu] 2
991 The JVM uses a similar mechanism to implement the feature of dumping
992 thread stacks for debugging purposes.
993 The JVM uses \f[CB]CTRL_BREAK_EVENT\f[R] to perform thread dumps.
994 .IP \[bu] 2
995 If the JVM is run as a service (for example, as a servlet engine for a
996 web server), then it can receive \f[CB]CTRL_LOGOFF_EVENT\f[R] but
997 shouldn\[aq]t initiate shutdown because the operating system doesn\[aq]t
998 actually terminate the process.
999 To avoid possible interference such as this, the \f[CB]\-Xrs\f[R] option
1000 can be used.
1001 When the \f[CB]\-Xrs\f[R] option is used, the JVM doesn\[aq]t install a
1002 console control handler, implying that it doesn\[aq]t watch for or
1003 process \f[CB]CTRL_C_EVENT\f[R], \f[CB]CTRL_CLOSE_EVENT\f[R],
1004 \f[CB]CTRL_LOGOFF_EVENT\f[R], or \f[CB]CTRL_SHUTDOWN_EVENT\f[R].
1005 .RE
1006 .PP
1007 There are two consequences of specifying \f[CB]\-Xrs\f[R]:
1008 .IP \[bu] 2
1009 \f[B]Oracle Solaris, Linux, and macOS:\f[R] \f[CB]SIGQUIT\f[R] thread dumps
1010 aren\[aq]t available.
1011 .IP \[bu] 2
1012 \f[B]Windows:\f[R] Ctrl + Break thread dumps aren\[aq]t available.
1013 .PP
1014 User code is responsible for causing shutdown hooks to run, for example,
1015 by calling the \f[CB]System.exit()\f[R] when the JVM is to be terminated.
1016 .RE
1017 .TP
1018 .B \f[CB]\-Xshare:\f[R]\f[I]mode\f[R]
1019 Sets the class data sharing (CDS) mode.
1020 .RS
1021 .PP
1022 Possible \f[I]mode\f[R] arguments for this option include the following:
1023 .TP
1024 .B \f[CB]auto\f[R]
1025 Use shared class data if possible (default).
1026 .RS
1027 .RE
1028 .TP
1029 .B \f[CB]on\f[R]
1030 Require using shared class data, otherwise fail.
1031 .RS
1032 .RE
1033 .RS
1034 .PP
1035 \f[B]Note:\f[R] The \f[CB]\-Xshare:on\f[R] option is used for testing
1036 purposes only and may cause intermittent failures due to the use of
1037 address space layout randomization by the operation system.
1038 This option should not be used in production environments.
1039 .RE
1040 .TP
1041 .B \f[CB]off\f[R]
1042 Do not attempt to use shared class data.
1043 .RS
1044 .RE
1045 .RE
1046 .TP
1047 .B \f[CB]\-XshowSettings\f[R]
1048 Shows all settings and then continues.
1049 .RS
1050 .RE
1051 .TP
1052 .B \f[CB]\-XshowSettings:\f[R]\f[I]category\f[R]
1053 Shows settings and continues.
1054 Possible \f[I]category\f[R] arguments for this option include the
1055 following:
1056 .RS
1057 .TP
1058 .B \f[CB]all\f[R]
1059 Shows all categories of settings.
1060 This is the default value.
1061 .RS
1062 .RE
1063 .TP
1064 .B \f[CB]locale\f[R]
1065 Shows settings related to locale.
1066 .RS
1067 .RE
1068 .TP
1069 .B \f[CB]properties\f[R]
1070 Shows settings related to system properties.
1071 .RS
1072 .RE
1073 .TP
1074 .B \f[CB]vm\f[R]
1075 Shows the settings of the JVM.
1076 .RS
1077 .RE
1078 .TP
1079 .B \f[CB]system\f[R]
1080 \f[B]Linux:\f[R] Shows host system or container configuration and
1081 continues.
1082 .RS
1083 .RE
1084 .RE
1085 .TP
1086 .B \f[CB]\-Xss\f[R] \f[I]size\f[R]
1087 Sets the thread stack size (in bytes).
1088 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate KB, \f[CB]m\f[R] or
1089 \f[CB]M\f[R] to indicate MB, or \f[CB]g\f[R] or \f[CB]G\f[R] to indicate GB.
1090 The default value depends on the platform:
1091 .RS
1092 .IP \[bu] 2
1093 Linux/x64 (64\-bit): 1024 KB
1094 .IP \[bu] 2
1095 macOS (64\-bit): 1024 KB
1096 .IP \[bu] 2
1097 Oracle Solaris (64\-bit): 1024 KB
1098 .IP \[bu] 2
1099 Windows: The default value depends on virtual memory
1100 .PP
1101 The following examples set the thread stack size to 1024 KB in different
1102 units:
1103 .IP
1104 .nf
1105 \f[CB]
1106 \-Xss1m
1107 \-Xss1024k
1108 \-Xss1048576
1109 \f[R]
1110 .fi
1111 .PP
1112 This option is similar to \f[CB]\-XX:ThreadStackSize\f[R].
1113 .RE
1114 .TP
1115 .B \f[CB]\-\-add\-reads\f[R] \f[I]module\f[R]\f[CB]=\f[R]\f[I]target\-module\f[R](\f[CB],\f[R]\f[I]target\-module\f[R])*
1116 Updates \f[I]module\f[R] to read the \f[I]target\-module\f[R], regardless
1117 of the module declaration.
1118 \f[I]target\-module\f[R] can be all unnamed to read all unnamed modules.
1119 .RS
1120 .RE
1121 .TP
1122 .B \f[CB]\-\-add\-exports\f[R] \f[I]module\f[R]\f[CB]/\f[R]\f[I]package\f[R]\f[CB]=\f[R]\f[I]target\-module\f[R](\f[CB],\f[R]\f[I]target\-module\f[R])*
1123 Updates \f[I]module\f[R] to export \f[I]package\f[R] to
1124 \f[I]target\-module\f[R], regardless of module declaration.
1125 The \f[I]target\-module\f[R] can be all unnamed to export to all unnamed
1126 modules.
1127 .RS
1128 .RE
1129 .TP
1130 .B \f[CB]\-\-add\-opens\f[R] \f[I]module\f[R]\f[CB]/\f[R]\f[I]package\f[R]\f[CB]=\f[R]\f[I]target\-module\f[R](\f[CB],\f[R]\f[I]target\-module\f[R])*
1131 Updates \f[I]module\f[R] to open \f[I]package\f[R] to
1132 \f[I]target\-module\f[R], regardless of module declaration.
1133 .RS
1134 .RE
1135 .TP
1136 .B \f[CB]\-\-illegal\-access=\f[R]\f[I]parameter\f[R]
1137 When present at run time, \f[CB]\-\-illegal\-access=\f[R] takes a keyword
1138 \f[I]parameter\f[R] to specify a mode of operation:
1139 .RS
1140 .RS
1141 .PP
1142 \f[B]Note:\f[R] This option will be removed in a future release.
1143 .RE
1144 .IP \[bu] 2
1145 \f[CB]permit\f[R]: This mode opens each package in each module in the
1146 run\-time image to code in all unnamed modules ( such as code on the
1147 class path), if that package existed in JDK 8.
1148 This enables both static access, (for example, by compiled bytecode, and
1149 deep reflective access) through the platform\[aq]s various reflection
1150 APIs.
1151 The first reflective\-access operation to any such package causes a
1152 warning to be issued.
1153 However, no warnings are issued after the first occurrence.
1154 This single warning describes how to enable further warnings.
1155 This mode is the default for the current JDK but will change in a future
1156 release.
1157 .IP \[bu] 2
1158 \f[CB]warn\f[R]: This mode is identical to \f[CB]permit\f[R] except that a
1159 warning message is issued for each illegal reflective\-access operation.
1160 .IP \[bu] 2
1161 \f[CB]debug\f[R]: This mode is identical to \f[CB]warn\f[R] except that both
1162 a warning message and a stack trace are issued for each illegal
1163 reflective\-access operation.
1164 .IP \[bu] 2
1165 \f[CB]deny\f[R]: This mode disables all illegal\-access operations except
1166 for those enabled by other command\-line options, such as
1167 \f[CB]\-\-add\-opens\f[R].
1168 This mode will become the default in a future release.
1169 .PP
1170 The default mode, \f[CB]\-\-illegal\-access=permit\f[R], is intended to
1171 make you aware of code on the class path that reflectively accesses any
1172 JDK\-internal APIs at least once.
1173 To learn about all such accesses, you can use the \f[CB]warn\f[R] or the
1174 \f[CB]debug\f[R] modes.
1175 For each library or framework on the class path that requires illegal
1176 access, you have two options:
1177 .IP \[bu] 2
1178 If the component\[aq]s maintainers have already released a fixed version
1179 that no longer uses JDK\-internal APIs then you can consider upgrading
1180 to that version.
1181 .IP \[bu] 2
1182 If the component still needs to be fixed, then you can contact its
1183 maintainers and ask them to replace their use of JDK\-internal APIs with
1184 the proper exported APIs.
1185 .PP
1186 If you must continue to use a component that requires illegal access,
1187 then you can eliminate the warning messages by using one or more
1188 \f[CB]\-\-add\-opens\f[R] options to open only those internal packages to
1189 which access is required.
1190 .PP
1191 To verify that your application is ready for a future version of the
1192 JDK, run it with \f[CB]\-\-illegal\-access=deny\f[R] along with any
1193 necessary \f[CB]\-\-add\-opens\f[R] options.
1194 Any remaining illegal\-access errors will most likely be due to static
1195 references from compiled code to JDK\-internal APIs.
1196 You can identify those by running the \f[B]jdeps\f[R] tool with the
1197 \f[CB]\-\-jdk\-internals\f[R] option.
1198 For performance reasons, the current JDK does not issue warnings for
1199 illegal static\-access operations.
1200 .RE
1201 .TP
1202 .B \f[CB]\-\-limit\-modules\f[R] \f[I]module\f[R][\f[CB],\f[R]\f[I]module\f[R]...]
1203 Specifies the limit of the universe of observable modules.
1204 .RS
1205 .RE
1206 .TP
1207 .B \f[CB]\-\-patch\-module\f[R] \f[I]module\f[R]\f[CB]=\f[R]\f[I]file\f[R](\f[CB];\f[R]\f[I]file\f[R])*
1208 Overrides or augments a module with classes and resources in JAR files
1209 or directories.
1210 .RS
1211 .RE
1212 .TP
1213 .B \f[CB]\-\-source\f[R] \f[I]version\f[R]
1214 Sets the version of the source in source\-file mode.
1215 .RS
1216 .RE
1217 .SH EXTRA OPTIONS FOR MACOS
1218 .PP
1219 The following extra options are macOS specific.
1220 .TP
1221 .B \f[CB]\-XstartOnFirstThread\f[R]
1222 Runs the \f[CB]main()\f[R] method on the first (AppKit) thread.
1223 .RS
1224 .RE
1225 .TP
1226 .B \f[CB]\-Xdock:name=\f[R]\f[I]application_name\f[R]
1227 Overrides the default application name displayed in dock.
1228 .RS
1229 .RE
1230 .TP
1231 .B \f[CB]\-Xdock:icon=\f[R]\f[I]path_to_icon_file\f[R]
1232 Overrides the default icon displayed in dock.
1233 .RS
1234 .RE
1235 .SH ADVANCED OPTIONS FOR JAVA
1236 .PP
1237 These \f[CB]java\f[R] options can be used to enable other advanced
1238 options.
1239 .TP
1240 .B \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R]
1241 Unlocks the options intended for diagnosing the JVM.
1242 By default, this option is disabled and diagnostic options aren\[aq]t
1243 available.
1244 .RS
1245 .PP
1246 Command line options that are enabled with the use of this option are
1247 not supported.
1248 If you encounter issues while using any of these options, it is very
1249 likely that you will be required to reproduce the problem without using
1250 any of these unsupported options before Oracle Support can assist with
1251 an investigation.
1252 It is also possible that any of these options may be removed or their
1253 behavior changed without any warning.
1254 .RE
1255 .TP
1256 .B \f[CB]\-XX:+UnlockExperimentalVMOptions\f[R]
1257 Unlocks the options that provide experimental features in the JVM.
1258 By default, this option is disabled and experimental features aren\[aq]t
1259 available.
1260 .RS
1261 .RE
1262 .SH ADVANCED RUNTIME OPTIONS FOR JAVA
1263 .PP
1264 These \f[CB]java\f[R] options control the runtime behavior of the Java
1265 HotSpot VM.
1266 .TP
1267 .B \f[CB]\-XX:ActiveProcessorCount=\f[R]\f[I]x\f[R]
1268 Overrides the number of CPUs that the VM will use to calculate the size
1269 of thread pools it will use for various operations such as Garbage
1270 Collection and ForkJoinPool.
1271 .RS
1272 .PP
1273 The VM normally determines the number of available processors from the
1274 operating system.
1275 This flag can be useful for partitioning CPU resources when running
1276 multiple Java processes in docker containers.
1277 This flag is honored even if \f[CB]UseContainerSupport\f[R] is not
1278 enabled.
1279 See \f[CB]\-XX:\-UseContainerSupport\f[R] for a description of enabling
1280 and disabling container support.
1281 .RE
1282 .TP
1283 .B \f[CB]\-XX:AllocateHeapAt=\f[R]\f[I]path\f[R]
1284 Takes a path to the file system and uses memory mapping to allocate the
1285 object heap on the memory device.
1286 Using this option enables the HotSpot VM to allocate the Java object
1287 heap on an alternative memory device, such as an NV\-DIMM, specified by
1288 the user.
1289 .RS
1290 .PP
1291 Alternative memory devices that have the same semantics as DRAM,
1292 including the semantics of atomic operations, can be used instead of
1293 DRAM for the object heap without changing the existing application code.
1294 All other memory structures (such as the code heap, metaspace, and
1295 thread stacks) continue to reside in DRAM.
1296 .PP
1297 Some operating systems expose non\-DRAM memory through the file system.
1298 Memory\-mapped files in these file systems bypass the page cache and
1299 provide a direct mapping of virtual memory to the physical memory on the
1300 device.
1301 The existing heap related flags (such as \f[CB]\-Xmx\f[R] and
1302 \f[CB]\-Xms\f[R]) and garbage\-collection related flags continue to work
1303 as before.
1304 .RE
1305 .TP
1306 .B \f[CB]\-XX:\-CompactStrings\f[R]
1307 Disables the Compact Strings feature.
1308 By default, this option is enabled.
1309 When this option is enabled, Java Strings containing only single\-byte
1310 characters are internally represented and stored as
1311 single\-byte\-per\-character Strings using ISO\-8859\-1 / Latin\-1
1312 encoding.
1313 This reduces, by 50%, the amount of space required for Strings
1314 containing only single\-byte characters.
1315 For Java Strings containing at least one multibyte character: these are
1316 represented and stored as 2 bytes per character using UTF\-16 encoding.
1317 Disabling the Compact Strings feature forces the use of UTF\-16 encoding
1318 as the internal representation for all Java Strings.
1319 .RS
1320 .PP
1321 Cases where it may be beneficial to disable Compact Strings include the
1322 following:
1323 .IP \[bu] 2
1324 When it\[aq]s known that an application overwhelmingly will be
1325 allocating multibyte character Strings
1326 .IP \[bu] 2
1327 In the unexpected event where a performance regression is observed in
1328 migrating from Java SE 8 to Java SE 9 and an analysis shows that Compact
1329 Strings introduces the regression
1330 .PP
1331 In both of these scenarios, disabling Compact Strings makes sense.
1332 .RE
1333 .TP
1334 .B \f[CB]\-XX:ErrorFile=\f[R]\f[I]filename\f[R]
1335 Specifies the path and file name to which error data is written when an
1336 irrecoverable error occurs.
1337 By default, this file is created in the current working directory and
1338 named \f[CB]hs_err_pid\f[R]\f[I]pid\f[R]\f[CB]\&.log\f[R] where \f[I]pid\f[R]
1339 is the identifier of the process that encountered the error.
1340 .RS
1341 .PP
1342 The following example shows how to set the default log file (note that
1343 the identifier of the process is specified as \f[CB]%p\f[R]):
1344 .RS
1345 .PP
1346 \f[CB]\-XX:ErrorFile=./hs_err_pid%p.log\f[R]
1347 .RE
1348 .IP \[bu] 2
1349 \f[B]Oracle Solaris, Linux, and macOS:\f[R] The following example shows
1350 how to set the error log to \f[CB]/var/log/java/java_error.log\f[R]:
1351 .RS 2
1352 .RS
1353 .PP
1354 \f[CB]\-XX:ErrorFile=/var/log/java/java_error.log\f[R]
1355 .RE
1356 .RE
1357 .IP \[bu] 2
1358 \f[B]Windows:\f[R] The following example shows how to set the error log
1359 file to \f[CB]C:/log/java/java_error.log\f[R]:
1360 .RS 2
1361 .RS
1362 .PP
1363 \f[CB]\-XX:ErrorFile=C:/log/java/java_error.log\f[R]
1364 .RE
1365 .RE
1366 .PP
1367 If the file exists, and is writeable, then it will be overwritten.
1368 Otherwise, if the file can\[aq]t be created in the specified directory
1369 (due to insufficient space, permission problem, or another issue), then
1370 the file is created in the temporary directory for the operating system:
1371 .IP \[bu] 2
1372 \f[B]Oracle Solaris, Linux, and macOS:\f[R] The temporary directory is
1373 \f[CB]/tmp\f[R].
1374 .IP \[bu] 2
1375 \f[B]Windows:\f[R] The temporary directory is specified by the value of
1376 the \f[CB]TMP\f[R] environment variable; if that environment variable
1377 isn\[aq]t defined, then the value of the \f[CB]TEMP\f[R] environment
1378 variable is used.
1379 .RE
1380 .TP
1381 .B \f[CB]\-XX:+ExtensiveErrorReports\f[R]
1382 Enables the reporting of more extensive error information in the
1383 \f[CB]ErrorFile\f[R].
1384 This option can be turned on in environments where maximal information
1385 is desired \- even if the resulting logs may be quite large and/or
1386 contain information that might be considered sensitive.
1387 The information can vary from release to release, and across different
1388 platforms.
1389 By default this option is disabled.
1390 .RS
1391 .RE
1392 .TP
1393 .B \f[CB]\-XX:FlightRecorderOptions=\f[R]\f[I]parameter\f[R]\f[CB]=\f[R]\f[I]value\f[R] (or)\f[CB]\-XX:FlightRecorderOptions:\f[R]\f[I]parameter\f[R]\f[CB]=\f[R]\f[I]value\f[R]
1394 Sets the parameters that control the behavior of JFR.
1395 .RS
1396 .PP
1397 The following list contains the available JFR
1398 \f[I]parameter\f[R]\f[CB]=\f[R]\f[I]value\f[R] entries:
1399 .TP
1400 .B \f[CB]globalbuffersize=\f[R]\f[I]size\f[R]
1401 Specifies the total amount of primary memory used for data retention.
1402 The default value is based on the value specified for
1403 \f[CB]memorysize\f[R].
1404 Change the \f[CB]memorysize\f[R] parameter to alter the size of global
1405 buffers.
1406 .RS
1407 .RE
1408 .TP
1409 .B \f[CB]maxchunksize=\f[R]\f[I]size\f[R]
1410 Specifies the maximum size (in bytes) of the data chunks in a recording.
1411 Append \f[CB]m\f[R] or \f[CB]M\f[R] to specify the size in megabytes (MB),
1412 or \f[CB]g\f[R] or \f[CB]G\f[R] to specify the size in gigabytes (GB).
1413 By default, the maximum size of data chunks is set to 12 MB.
1414 The minimum allowed is 1 MB.
1415 .RS
1416 .RE
1417 .TP
1418 .B \f[CB]memorysize=\f[R]\f[I]size\f[R]
1419 Determines how much buffer memory should be used, and sets the
1420 \f[CB]globalbuffersize\f[R] and \f[CB]numglobalbuffers\f[R] parameters based
1421 on the size specified.
1422 Append \f[CB]m\f[R] or \f[CB]M\f[R] to specify the size in megabytes (MB),
1423 or \f[CB]g\f[R] or \f[CB]G\f[R] to specify the size in gigabytes (GB).
1424 By default, the memory size is set to 10 MB.
1425 .RS
1426 .RE
1427 .TP
1428 .B \f[CB]numglobalbuffers\f[R]
1429 Specifies the number of global buffers used.
1430 The default value is based on the memory size specified.
1431 Change the \f[CB]memorysize\f[R] parameter to alter the number of global
1432 buffers.
1433 .RS
1434 .RE
1435 .TP
1436 .B \f[CB]old\-object\-queue\-size=number\-of\-objects\f[R]
1437 Maximum number of old objects to track.
1438 By default, the number of objects is set to 256.
1439 .RS
1440 .RE
1441 .TP
1442 .B \f[CB]repository=\f[R]\f[I]path\f[R]
1443 Specifies the repository (a directory) for temporary disk storage.
1444 By default, the system\[aq]s temporary directory is used.
1445 .RS
1446 .RE
1447 .TP
1448 .B \f[CB]retransform=\f[R]{\f[CB]true\f[R]|\f[CB]false\f[R]}
1449 Specifies whether event classes should be retransformed using JVMTI.
1450 If false, instrumentation is added when event classes are loaded.
1451 By default, this parameter is enabled.
1452 .RS
1453 .RE
1454 .TP
1455 .B \f[CB]samplethreads=\f[R]{\f[CB]true\f[R]|\f[CB]false\f[R]}
1456 Specifies whether thread sampling is enabled.
1457 Thread sampling occurs only if the sampling event is enabled along with
1458 this parameter.
1459 By default, this parameter is enabled.
1460 .RS
1461 .RE
1462 .TP
1463 .B \f[CB]stackdepth=\f[R]\f[I]depth\f[R]
1464 Stack depth for stack traces.
1465 By default, the depth is set to 64 method calls.
1466 The maximum is 2048.
1467 Values greater than 64 could create significant overhead and reduce
1468 performance.
1469 .RS
1470 .RE
1471 .TP
1472 .B \f[CB]threadbuffersize=\f[R]\f[I]size\f[R]
1473 Specifies the per\-thread local buffer size (in bytes).
1474 By default, the local buffer size is set to 8 kilobytes, with a minimum
1475 value of 4 kilobytes.
1476 Overriding this parameter could reduce performance and is not
1477 recommended.
1478 .RS
1479 .RE
1480 .PP
1481 You can specify values for multiple parameters by separating them with a
1482 comma.
1483 .RE
1484 .TP
1485 .B \f[CB]\-XX:LargePageSizeInBytes=\f[R]\f[I]size\f[R]
1486 Sets the maximum size (in bytes) for large pages used for the Java heap.
1487 The \f[I]size\f[R] argument must be a power of 2 (2, 4, 8, 16, and so
1488 on).
1489 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
1490 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
1491 \f[CB]G\f[R] to indicate gigabytes.
1492 By default, the size is set to 0, meaning that the JVM chooses the size
1493 for large pages automatically.
1494 See \f[B]Large Pages\f[R].
1495 .RS
1496 .PP
1497 The following example describes how to set the large page size to 4
1498 megabytes (MB):
1499 .RS
1500 .PP
1501 \f[CB]\-XX:LargePageSizeInBytes=4m\f[R]
1502 .RE
1503 .RE
1504 .TP
1505 .B \f[CB]\-XX:MaxDirectMemorySize=\f[R]\f[I]size\f[R]
1506 Sets the maximum total size (in bytes) of the \f[CB]java.nio\f[R] package,
1507 direct\-buffer allocations.
1508 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
1509 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
1510 \f[CB]G\f[R] to indicate gigabytes.
1511 By default, the size is set to 0, meaning that the JVM chooses the size
1512 for NIO direct\-buffer allocations automatically.
1513 .RS
1514 .PP
1515 The following examples illustrate how to set the NIO size to 1024 KB in
1516 different units:
1517 .IP
1518 .nf
1519 \f[CB]
1520 \-XX:MaxDirectMemorySize=1m
1521 \-XX:MaxDirectMemorySize=1024k
1522 \-XX:MaxDirectMemorySize=1048576
1523 \f[R]
1524 .fi
1525 .RE
1526 .TP
1527 .B \f[CB]\-XX:\-MaxFDLimit\f[R]
1528 Disables the attempt to set the soft limit for the number of open file
1529 descriptors to the hard limit.
1530 By default, this option is enabled on all platforms, but is ignored on
1531 Windows.
1532 The only time that you may need to disable this is on Mac OS, where its
1533 use imposes a maximum of 10240, which is lower than the actual system
1534 maximum.
1535 .RS
1536 .RE
1537 .TP
1538 .B \f[CB]\-XX:NativeMemoryTracking=\f[R]\f[I]mode\f[R]
1539 Specifies the mode for tracking JVM native memory usage.
1540 Possible \f[I]mode\f[R] arguments for this option include the following:
1541 .RS
1542 .TP
1543 .B \f[CB]off\f[R]
1544 Instructs not to track JVM native memory usage.
1545 This is the default behavior if you don\[aq]t specify the
1546 \f[CB]\-XX:NativeMemoryTracking\f[R] option.
1547 .RS
1548 .RE
1549 .TP
1550 .B \f[CB]summary\f[R]
1551 Tracks memory usage only by JVM subsystems, such as Java heap, class,
1552 code, and thread.
1553 .RS
1554 .RE
1555 .TP
1556 .B \f[CB]detail\f[R]
1557 In addition to tracking memory usage by JVM subsystems, track memory
1558 usage by individual \f[CB]CallSite\f[R], individual virtual memory region
1559 and its committed regions.
1560 .RS
1561 .RE
1562 .RE
1563 .TP
1564 .B \f[CB]\-XX:ObjectAlignmentInBytes=\f[R]\f[I]alignment\f[R]
1565 Sets the memory alignment of Java objects (in bytes).
1566 By default, the value is set to 8 bytes.
1567 The specified value should be a power of 2, and must be within the range
1568 of 8 and 256 (inclusive).
1569 This option makes it possible to use compressed pointers with large Java
1570 heap sizes.
1571 .RS
1572 .PP
1573 The heap size limit in bytes is calculated as:
1574 .RS
1575 .PP
1576 \f[CB]4GB\ *\ ObjectAlignmentInBytes\f[R]
1577 .RE
1578 .RS
1579 .PP
1580 \f[B]Note:\f[R] As the alignment value increases, the unused space
1581 between objects also increases.
1582 As a result, you may not realize any benefits from using compressed
1583 pointers with large Java heap sizes.
1584 .RE
1585 .RE
1586 .TP
1587 .B \f[CB]\-XX:OnError=\f[R]\f[I]string\f[R]
1588 Sets a custom command or a series of semicolon\-separated commands to
1589 run when an irrecoverable error occurs.
1590 If the string contains spaces, then it must be enclosed in quotation
1591 marks.
1592 .RS
1593 .IP \[bu] 2
1594 \f[B]Oracle Solaris, Linux, and macOS:\f[R] The following example shows
1595 how the \f[CB]\-XX:OnError\f[R] option can be used to run the
1596 \f[CB]gcore\f[R] command to create a core image, and start the
1597 \f[CB]gdb\f[R] debugger to attach to the process in case of an
1598 irrecoverable error (the \f[CB]%p\f[R] designates the current process
1599 identifier):
1600 .RS 2
1601 .RS
1602 .PP
1603 \f[CB]\-XX:OnError="gcore\ %p;gdb\ \-p\ %p"\f[R]
1604 .RE
1605 .RE
1606 .IP \[bu] 2
1607 \f[B]Windows:\f[R] The following example shows how the
1608 \f[CB]\-XX:OnError\f[R] option can be used to run the
1609 \f[CB]userdump.exe\f[R] utility to obtain a crash dump in case of an
1610 irrecoverable error (the \f[CB]%p\f[R] designates the current process
1611 identifier).
1612 This example assumes that the path to the \f[CB]userdump.exe\f[R] utility
1613 is specified in the \f[CB]PATH\f[R] environment variable:
1614 .RS 2
1615 .RS
1616 .PP
1617 \f[CB]\-XX:OnError="userdump.exe\ %p"\f[R]
1618 .RE
1619 .RE
1620 .RE
1621 .TP
1622 .B \f[CB]\-XX:OnOutOfMemoryError=\f[R]\f[I]string\f[R]
1623 Sets a custom command or a series of semicolon\-separated commands to
1624 run when an \f[CB]OutOfMemoryError\f[R] exception is first thrown.
1625 If the string contains spaces, then it must be enclosed in quotation
1626 marks.
1627 For an example of a command string, see the description of the
1628 \f[CB]\-XX:OnError\f[R] option.
1629 .RS
1630 .RE
1631 .TP
1632 .B \f[CB]\-XX:+PrintCommandLineFlags\f[R]
1633 Enables printing of ergonomically selected JVM flags that appeared on
1634 the command line.
1635 It can be useful to know the ergonomic values set by the JVM, such as
1636 the heap space size and the selected garbage collector.
1637 By default, this option is disabled and flags aren\[aq]t printed.
1638 .RS
1639 .RE
1640 .TP
1641 .B \f[CB]\-XX:+PreserveFramePointer\f[R]
1642 Selects between using the RBP register as a general purpose register
1643 (\f[CB]\-XX:\-PreserveFramePointer\f[R]) and using the RBP register to
1644 hold the frame pointer of the currently executing method
1645 (\f[CB]\-XX:+PreserveFramePointer\f[R] .
1646 If the frame pointer is available, then external profiling tools\ (for
1647 example, Linux perf) can construct more accurate stack traces.
1648 .RS
1649 .RE
1650 .TP
1651 .B \f[CB]\-XX:+PrintNMTStatistics\f[R]
1652 Enables printing of collected native memory tracking data at JVM exit
1653 when native memory tracking is enabled (see
1654 \f[CB]\-XX:NativeMemoryTracking\f[R]).
1655 By default, this option is disabled and native memory tracking data
1656 isn\[aq]t printed.
1657 .RS
1658 .RE
1659 .TP
1660 .B \f[CB]\-XX:SharedArchiveFile=\f[R]\f[I]path\f[R]
1661 Specifies the path and name of the class data sharing (CDS) archive file
1662 .RS
1663 .PP
1664 See \f[B]Application Class Data Sharing\f[R].
1665 .RE
1666 .TP
1667 .B \f[CB]\-XX:SharedArchiveConfigFile\f[R]=\f[I]shared_config_file\f[R]
1668 Specifies additional shared data added to the archive file.
1669 .RS
1670 .RE
1671 .TP
1672 .B \f[CB]\-XX:SharedClassListFile=\f[R]\f[I]file_name\f[R]
1673 Specifies the text file that contains the names of the classes to store
1674 in the class data sharing (CDS) archive.
1675 This file contains the full name of one class per line, except slashes
1676 (\f[CB]/\f[R]) replace dots (\f[CB]\&.\f[R]).
1677 For example, to specify the classes \f[CB]java.lang.Object\f[R] and
1678 \f[CB]hello.Main\f[R], create a text file that contains the following two
1679 lines:
1680 .RS
1681 .IP
1682 .nf
1683 \f[CB]
1684 java/lang/Object
1685 hello/Main
1686 \f[R]
1687 .fi
1688 .PP
1689 The classes that you specify in this text file should include the
1690 classes that are commonly used by the application.
1691 They may include any classes from the application, extension, or
1692 bootstrap class paths.
1693 .PP
1694 See \f[B]Application Class Data Sharing\f[R].
1695 .RE
1696 .TP
1697 .B \f[CB]\-XX:+ShowMessageBoxOnError\f[R]
1698 Enables the display of a dialog box when the JVM experiences an
1699 irrecoverable error.
1700 This prevents the JVM from exiting and keeps the process active so that
1701 you can attach a debugger to it to investigate the cause of the error.
1702 By default, this option is disabled.
1703 .RS
1704 .RE
1705 .TP
1706 .B \f[CB]\-XX:StartFlightRecording=\f[R]\f[I]parameter\f[R]\f[CB]=\f[R]\f[I]value\f[R]
1707 Starts a JFR recording for the Java application.
1708 This option is equivalent to the \f[CB]JFR.start\f[R] diagnostic command
1709 that starts a recording during runtime.
1710 You can set the following \f[I]parameter\f[R]\f[CB]=\f[R]\f[I]value\f[R]
1711 entries when starting a JFR recording:
1712 .RS
1713 .TP
1714 .B \f[CB]delay=\f[R]\f[I]time\f[R]
1715 Specifies the delay between the Java application launch time and the
1716 start of the recording.
1717 Append \f[CB]s\f[R] to specify the time in seconds, \f[CB]m\f[R] for
1718 minutes, \f[CB]h\f[R] for hours, or \f[CB]d\f[R] for days (for example,
1719 specifying \f[CB]10m\f[R] means 10 minutes).
1720 By default, there\[aq]s no delay, and this parameter is set to 0.
1721 .RS
1722 .RE
1723 .TP
1724 .B \f[CB]disk=\f[R]{\f[CB]true\f[R]|\f[CB]false\f[R]}
1725 Specifies whether to write data to disk while recording.
1726 By default, this parameter is enabled.
1727 .RS
1728 .RE
1729 .TP
1730 .B \f[CB]dumponexit=\f[R]{\f[CB]true\f[R]|\f[CB]false\f[R]}
1731 Specifies if the running recording is dumped when the JVM shuts down.
1732 If enabled and a \f[CB]filename\f[R] is not entered, the recording is
1733 written to a file in the directory where the process was started.
1734 The file name is a system\-generated name that contains the process ID,
1735 recording ID, and current timestamp, similar to
1736 \f[CB]hotspot\-pid\-47496\-id\-1\-2018_01_25_19_10_41.jfr\f[R].
1737 By default, this parameter is disabled.
1738 .RS
1739 .RE
1740 .TP
1741 .B \f[CB]duration=\f[R]\f[I]time\f[R]
1742 Specifies the duration of the recording.
1743 Append \f[CB]s\f[R] to specify the time in seconds, \f[CB]m\f[R] for
1744 minutes, \f[CB]h\f[R] for hours, or \f[CB]d\f[R] for days (for example,
1745 specifying \f[CB]5h\f[R] means 5 hours).
1746 By default, the duration isn\[aq]t limited, and this parameter is set to
1747 0.
1748 .RS
1749 .RE
1750 .TP
1751 .B \f[CB]filename=\f[R]\f[I]path\f[R]
1752 Specifies the path and name of the file to which the recording is
1753 written when the recording is stopped, for example:
1754 .RS
1755 .IP \[bu] 2
1756 \f[CB]recording.jfr\f[R]
1757 .IP \[bu] 2
1758 \f[CB]/home/user/recordings/recording.jfr\f[R]
1759 .IP \[bu] 2
1760 \f[CB]c:\\recordings\\recording.jfr\f[R]
1761 .RE
1762 .TP
1763 .B \f[CB]name=\f[R]\f[I]identifier\f[R]
1764 Takes both the name and the identifier of a recording.
1765 .RS
1766 .RE
1767 .TP
1768 .B \f[CB]maxage=\f[R]\f[I]time\f[R]
1769 Specifies the maximum age of disk data to keep for the recording.
1770 This parameter is valid only when the \f[CB]disk\f[R] parameter is set to
1771 \f[CB]true\f[R].
1772 Append \f[CB]s\f[R] to specify the time in seconds, \f[CB]m\f[R] for
1773 minutes, \f[CB]h\f[R] for hours, or \f[CB]d\f[R] for days (for example,
1774 specifying \f[CB]30s\f[R] means 30 seconds).
1775 By default, the maximum age isn\[aq]t limited, and this parameter is set
1776 to \f[CB]0s\f[R].
1777 .RS
1778 .RE
1779 .TP
1780 .B \f[CB]maxsize=\f[R]\f[I]size\f[R]
1781 Specifies the maximum size (in bytes) of disk data to keep for the
1782 recording.
1783 This parameter is valid only when the \f[CB]disk\f[R] parameter is set to
1784 \f[CB]true\f[R].
1785 The value must not be less than the value for the \f[CB]maxchunksize\f[R]
1786 parameter set with \f[CB]\-XX:FlightRecorderOptions\f[R].
1787 Append \f[CB]m\f[R] or \f[CB]M\f[R] to specify the size in megabytes, or
1788 \f[CB]g\f[R] or \f[CB]G\f[R] to specify the size in gigabytes.
1789 By default, the maximum size of disk data isn\[aq]t limited, and this
1790 parameter is set to \f[CB]0\f[R].
1791 .RS
1792 .RE
1793 .TP
1794 .B \f[CB]path\-to\-gc\-roots=\f[R]{\f[CB]true\f[R]|\f[CB]false\f[R]}
1795 Specifies whether to collect the path to garbage collection (GC) roots
1796 at the end of a recording.
1797 By default, this parameter is disabled.
1798 .RS
1799 .PP
1800 The path to GC roots is useful for finding memory leaks, but collecting
1801 it is time\-consuming.
1802 Enable this option only when you start a recording for an application
1803 that you suspect has a memory leak.
1804 If the \f[CB]settings\f[R] parameter is set to \f[CB]profile\f[R], the stack
1805 trace from where the potential leaking object was allocated is included
1806 in the information collected.
1807 .RE
1808 .TP
1809 .B \f[CB]settings=\f[R]\f[I]path\f[R]
1810 Specifies the path and name of the event settings file (of type JFC).
1811 By default, the \f[CB]default.jfc\f[R] file is used, which is located in
1812 \f[CB]JRE_HOME/lib/jfr\f[R].
1813 This default settings file collects a predefined set of information with
1814 low overhead, so it has minimal impact on performance and can be used
1815 with recordings that run continuously.
1816 .RS
1817 .PP
1818 A second settings file is also provided, profile.jfc, which provides
1819 more data than the default configuration, but can have more overhead and
1820 impact performance.
1821 Use this configuration for short periods of time when more information
1822 is needed.
1823 .RE
1824 .PP
1825 You can specify values for multiple parameters by separating them with a
1826 comma.
1827 .RE
1828 .TP
1829 .B \f[CB]\-XX:ThreadStackSize=\f[R]\f[I]size\f[R]
1830 Sets the Java thread stack size (in kilobytes).
1831 Use of a scaling suffix, such as \f[CB]k\f[R], results in the scaling of
1832 the kilobytes value so that \f[CB]\-XX:ThreadStackSize=1k\f[R] sets the
1833 Java thread stack size\ to 1024*1024 bytes or 1 megabyte.
1834 The default value depends on the platform:
1835 .RS
1836 .IP \[bu] 2
1837 Linux/x64 (64\-bit): 1024 KB
1838 .IP \[bu] 2
1839 macOS (64\-bit): 1024 KB
1840 .IP \[bu] 2
1841 Oracle Solaris (64\-bit): 1024 KB
1842 .IP \[bu] 2
1843 Windows: The default value depends on virtual memory
1844 .PP
1845 The following examples show how to set the thread stack size to 1
1846 megabyte in different units:
1847 .IP
1848 .nf
1849 \f[CB]
1850 \-XX:ThreadStackSize=1k
1851 \-XX:ThreadStackSize=1024
1852 \f[R]
1853 .fi
1854 .PP
1855 This option is similar to \f[CB]\-Xss\f[R].
1856 .RE
1857 .TP
1858 .B \f[CB]\-XX:\-UseBiasedLocking\f[R]
1859 Disables the use of biased locking.
1860 Some applications with significant amounts of uncontended
1861 synchronization may attain significant speedups with this flag enabled,
1862 but applications with certain patterns of locking may see slowdowns.
1863 \&.
1864 .RS
1865 .PP
1866 By default, this option is enabled.
1867 .RE
1868 .TP
1869 .B \f[CB]\-XX:\-UseCompressedOops\f[R]
1870 Disables the use of compressed pointers.
1871 By default, this option is enabled, and compressed pointers are used.
1872 This will automatically limit the maximum ergonomically determined Java
1873 heap size to the maximum amount of memory that can be covered by
1874 compressed pointers.
1875 By default this range is 32 GB.
1876 .RS
1877 .PP
1878 With compressed oops enabled, object references are represented as
1879 32\-bit offsets instead of 64\-bit pointers, which typically increases
1880 performance when running the application with Java heap sizes smaller
1881 than the compressed oops pointer range.
1882 This option works only for 64\-bit JVMs.
1883 .PP
1884 It\[aq]s possible to use compressed pointers with Java heap sizes
1885 greater than 32 GB.
1886 See the \f[CB]\-XX:ObjectAlignmentInBytes\f[R] option.
1887 .RE
1888 .TP
1889 .B \f[CB]\-XX:\-UseContainerSupport\f[R]
1890 The VM now provides automatic container detection support, which allows
1891 the VM to determine the amount of memory and number of processors that
1892 are available to a Java process running in docker containers.
1893 It uses this information to allocate system resources.
1894 This support is only available on Linux x64 platforms.
1895 \ If supported, the default for this flag is\ \f[CB]true\f[R], and
1896 container support is enabled by default.
1897 \ It\ can be disabled with\ \f[CB]\-XX:\-UseContainerSupport\f[R].
1898 .RS
1899 .PP
1900 Unified Logging is available to help to diagnose issues related to this
1901 support.
1902 .PP
1903 Use \f[CB]\-Xlog:os+container=trace\f[R] for maximum logging of container
1904 information.
1905 See \f[B]Enable Logging with the JVM Unified Logging Framework\f[R] for a
1906 description of using Unified Logging.
1907 .RE
1908 .TP
1909 .B \f[CB]\-XX:+UseHugeTLBFS\f[R]
1910 \f[B]Linux only:\f[R] This option is the equivalent of specifying
1911 \f[CB]\-XX:+UseLargePages\f[R].
1912 This option is disabled by default.
1913 This option pre\-allocates all large pages up\-front, when memory is
1914 reserved; consequently the JVM can\[aq]t dynamically grow or shrink
1915 large pages memory areas; see \f[CB]\-XX:UseTransparentHugePages\f[R] if
1916 you want this behavior.
1917 .RS
1918 .PP
1919 See \f[B]Large Pages\f[R].
1920 .RE
1921 .TP
1922 .B \f[CB]\-XX:+UseLargePages\f[R]
1923 Enables the use of large page memory.
1924 By default, this option is disabled and large page memory isn\[aq]t
1925 used.
1926 .RS
1927 .PP
1928 See \f[B]Large Pages\f[R].
1929 .RE
1930 .TP
1931 .B \f[CB]\-XX:+UseTransparentHugePages\f[R]
1932 \f[B]Linux only:\f[R] Enables the use of large pages that can dynamically
1933 grow or shrink.
1934 This option is disabled by default.
1935 You may encounter performance problems with transparent huge pages as
1936 the OS moves other pages around to create huge pages; this option is
1937 made available for experimentation.
1938 .RS
1939 .RE
1940 .TP
1941 .B \f[CB]\-XX:+AllowUserSignalHandlers\f[R]
1942 Enables installation of signal handlers by the application.
1943 By default, this option is disabled and the application isn\[aq]t
1944 allowed to install signal handlers.
1945 .RS
1946 .RE
1947 .TP
1948 .B \f[CB]\-XX:VMOptionsFile=\f[R]\f[I]filename\f[R]
1949 Allows user to specify VM options in a file, for example,
1950 \f[CB]java\ \-XX:VMOptionsFile=/var/my_vm_options\ HelloWorld\f[R].
1951 .RS
1952 .RE
1953 .SH ADVANCED JIT COMPILER OPTIONS FOR JAVA
1954 .PP
1955 These \f[CB]java\f[R] options control the dynamic just\-in\-time (JIT)
1956 compilation performed by the Java HotSpot VM.
1957 .TP
1958 .B \f[CB]\-XX:AllocateInstancePrefetchLines=\f[R]\f[I]lines\f[R]
1959 Sets the number of lines to prefetch ahead of the instance allocation
1960 pointer.
1961 By default, the number of lines to prefetch is set to 1:
1962 .RS
1963 .RS
1964 .PP
1965 \f[CB]\-XX:AllocateInstancePrefetchLines=1\f[R]
1966 .RE
1967 .PP
1968 Only the Java HotSpot Server VM supports this option.
1969 .RE
1970 .TP
1971 .B \f[CB]\-XX:AllocatePrefetchDistance=\f[R]\f[I]size\f[R]
1972 Sets the size (in bytes) of the prefetch distance for object allocation.
1973 Memory about to be written with the value of new objects is prefetched
1974 up to this distance starting from the address of the last allocated
1975 object.
1976 Each Java thread has its own allocation point.
1977 .RS
1978 .PP
1979 Negative values denote that prefetch distance is chosen based on the
1980 platform.
1981 Positive values are bytes to prefetch.
1982 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
1983 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
1984 \f[CB]G\f[R] to indicate gigabytes.
1985 The default value is set to \-1.
1986 .PP
1987 The following example shows how to set the prefetch distance to 1024
1988 bytes:
1989 .RS
1990 .PP
1991 \f[CB]\-XX:AllocatePrefetchDistance=1024\f[R]
1992 .RE
1993 .PP
1994 Only the Java HotSpot Server VM supports this option.
1995 .RE
1996 .TP
1997 .B \f[CB]\-XX:AllocatePrefetchInstr=\f[R]\f[I]instruction\f[R]
1998 Sets the prefetch instruction to prefetch ahead of the allocation
1999 pointer.
2000 Only the Java HotSpot Server VM supports this option.
2001 Possible values are from 0 to 3.
2002 The actual instructions behind the values depend on the platform.
2003 By default, the prefetch instruction is set to 0:
2004 .RS
2005 .RS
2006 .PP
2007 \f[CB]\-XX:AllocatePrefetchInstr=0\f[R]
2008 .RE
2009 .PP
2010 Only the Java HotSpot Server VM supports this option.
2011 .RE
2012 .TP
2013 .B \f[CB]\-XX:AllocatePrefetchLines=\f[R]\f[I]lines\f[R]
2014 Sets the number of cache lines to load after the last object allocation
2015 by using the prefetch instructions generated in compiled code.
2016 The default value is 1 if the last allocated object was an instance, and
2017 3 if it was an array.
2018 .RS
2019 .PP
2020 The following example shows how to set the number of loaded cache lines
2021 to 5:
2022 .RS
2023 .PP
2024 \f[CB]\-XX:AllocatePrefetchLines=5\f[R]
2025 .RE
2026 .PP
2027 Only the Java HotSpot Server VM supports this option.
2028 .RE
2029 .TP
2030 .B \f[CB]\-XX:AllocatePrefetchStepSize=\f[R]\f[I]size\f[R]
2031 Sets the step size (in bytes) for sequential prefetch instructions.
2032 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
2033 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, \f[CB]g\f[R] or \f[CB]G\f[R]
2034 to indicate gigabytes.
2035 By default, the step size is set to 16 bytes:
2036 .RS
2037 .RS
2038 .PP
2039 \f[CB]\-XX:AllocatePrefetchStepSize=16\f[R]
2040 .RE
2041 .PP
2042 Only the Java HotSpot Server VM supports this option.
2043 .RE
2044 .TP
2045 .B \f[CB]\-XX:AllocatePrefetchStyle=\f[R]\f[I]style\f[R]
2046 Sets the generated code style for prefetch instructions.
2047 The \f[I]style\f[R] argument is an integer from 0 to 3:
2048 .RS
2049 .TP
2050 .B \f[CB]0\f[R]
2051 Don\[aq]t generate prefetch instructions.
2052 .RS
2053 .RE
2054 .TP
2055 .B \f[CB]1\f[R]
2056 Execute prefetch instructions after each allocation.
2057 This is the default parameter.
2058 .RS
2059 .RE
2060 .TP
2061 .B \f[CB]2\f[R]
2062 Use the thread\-local allocation block (TLAB) watermark pointer to
2063 determine when prefetch instructions are executed.
2064 .RS
2065 .RE
2066 .TP
2067 .B \f[CB]3\f[R]
2068 Use BIS instruction on SPARC for allocation prefetch.
2069 .RS
2070 .RE
2071 .PP
2072 Only the Java HotSpot Server VM supports this option.
2073 .RE
2074 .TP
2075 .B \f[CB]\-XX:+BackgroundCompilation\f[R]
2076 Enables background compilation.
2077 This option is enabled by default.
2078 To disable background compilation, specify
2079 \f[CB]\-XX:\-BackgroundCompilation\f[R] (this is equivalent to specifying
2080 \f[CB]\-Xbatch\f[R]).
2081 .RS
2082 .RE
2083 .TP
2084 .B \f[CB]\-XX:CICompilerCount=\f[R]\f[I]threads\f[R]
2085 Sets the number of compiler threads to use for compilation.
2086 By default, the number of threads is set to 2 for the server JVM, to 1
2087 for the client JVM, and it scales to the number of cores if tiered
2088 compilation is used.
2089 The following example shows how to set the number of threads to 2:
2090 .RS
2091 .RS
2092 .PP
2093 \f[CB]\-XX:CICompilerCount=2\f[R]
2094 .RE
2095 .RE
2096 .TP
2097 .B \f[CB]\-XX:CompileCommand=\f[R]\f[I]command\f[R]\f[CB],\f[R]\f[I]method\f[R][\f[CB],\f[R]\f[I]option\f[R]]
2098 Specifies a \f[I]command\f[R] to perform on a \f[I]method\f[R].
2099 For example, to exclude the \f[CB]indexOf()\f[R] method of the
2100 \f[CB]String\f[R] class from being compiled, use the following:
2101 .RS
2102 .RS
2103 .PP
2104 \f[CB]\-XX:CompileCommand=exclude,java/lang/String.indexOf\f[R]
2105 .RE
2106 .PP
2107 Note that the full class name is specified, including all packages and
2108 subpackages separated by a slash (\f[CB]/\f[R]).
2109 For easier cut\-and\-paste operations, it\[aq]s also possible to use the
2110 method name format produced by the \f[CB]\-XX:+PrintCompilation\f[R] and
2111 \f[CB]\-XX:+LogCompilation\f[R] options:
2112 .RS
2113 .PP
2114 \f[CB]\-XX:CompileCommand=exclude,java.lang.String::indexOf\f[R]
2115 .RE
2116 .PP
2117 If the method is specified without the signature, then the command is
2118 applied to all methods with the specified name.
2119 However, you can also specify the signature of the method in the class
2120 file format.
2121 In this case, you should enclose the arguments in quotation marks,
2122 because otherwise the shell treats the semicolon as a command end.
2123 For example, if you want to exclude only the \f[CB]indexOf(String)\f[R]
2124 method of the \f[CB]String\f[R] class from being compiled, use the
2125 following:
2126 .RS
2127 .PP
2128 \f[CB]\-XX:CompileCommand="exclude,java/lang/String.indexOf,(Ljava/lang/String;)I"\f[R]
2129 .RE
2130 .PP
2131 You can also use the asterisk (*) as a wildcard for class and method
2132 names.
2133 For example, to exclude all \f[CB]indexOf()\f[R] methods in all classes
2134 from being compiled, use the following:
2135 .RS
2136 .PP
2137 \f[CB]\-XX:CompileCommand=exclude,*.indexOf\f[R]
2138 .RE
2139 .PP
2140 The commas and periods are aliases for spaces, making it easier to pass
2141 compiler commands through a shell.
2142 You can pass arguments to \f[CB]\-XX:CompileCommand\f[R] using spaces as
2143 separators by enclosing the argument in quotation marks:
2144 .RS
2145 .PP
2146 \f[CB]\-XX:CompileCommand="exclude\ java/lang/String\ indexOf"\f[R]
2147 .RE
2148 .PP
2149 Note that after parsing the commands passed on the command line using
2150 the \f[CB]\-XX:CompileCommand\f[R] options, the JIT compiler then reads
2151 commands from the \f[CB]\&.hotspot_compiler\f[R] file.
2152 You can add commands to this file or specify a different file using the
2153 \f[CB]\-XX:CompileCommandFile\f[R] option.
2154 .PP
2155 To add several commands, either specify the \f[CB]\-XX:CompileCommand\f[R]
2156 option multiple times, or separate each argument with the new line
2157 separator (\f[CB]\\n\f[R]).
2158 The following commands are available:
2159 .TP
2160 .B \f[CB]break\f[R]
2161 Sets a breakpoint when debugging the JVM to stop at the beginning of
2162 compilation of the specified method.
2163 .RS
2164 .RE
2165 .TP
2166 .B \f[CB]compileonly\f[R]
2167 Excludes all methods from compilation except for the specified method.
2168 As an alternative, you can use the \f[CB]\-XX:CompileOnly\f[R] option,
2169 which lets you specify several methods.
2170 .RS
2171 .RE
2172 .TP
2173 .B \f[CB]dontinline\f[R]
2174 Prevents inlining of the specified method.
2175 .RS
2176 .RE
2177 .TP
2178 .B \f[CB]exclude\f[R]
2179 Excludes the specified method from compilation.
2180 .RS
2181 .RE
2182 .TP
2183 .B \f[CB]help\f[R]
2184 Prints a help message for the \f[CB]\-XX:CompileCommand\f[R] option.
2185 .RS
2186 .RE
2187 .TP
2188 .B \f[CB]inline\f[R]
2189 Attempts to inline the specified method.
2190 .RS
2191 .RE
2192 .TP
2193 .B \f[CB]log\f[R]
2194 Excludes compilation logging (with the \f[CB]\-XX:+LogCompilation\f[R]
2195 option) for all methods except for the specified method.
2196 By default, logging is performed for all compiled methods.
2197 .RS
2198 .RE
2199 .TP
2200 .B \f[CB]option\f[R]
2201 Passes a JIT compilation option to the specified method in place of the
2202 last argument (\f[CB]option\f[R]).
2203 The compilation option is set at the end, after the method name.
2204 For example, to enable the \f[CB]BlockLayoutByFrequency\f[R] option for
2205 the \f[CB]append()\f[R] method of the \f[CB]StringBuffer\f[R] class, use the
2206 following:
2207 .RS
2208 .RS
2209 .PP
2210 \f[CB]\-XX:CompileCommand=option,java/lang/StringBuffer.append,BlockLayoutByFrequency\f[R]
2211 .RE
2212 .PP
2213 You can specify multiple compilation options, separated by commas or
2214 spaces.
2215 .RE
2216 .TP
2217 .B \f[CB]print\f[R]
2218 Prints generated assembler code after compilation of the specified
2219 method.
2220 .RS
2221 .RE
2222 .TP
2223 .B \f[CB]quiet\f[R]
2224 Instructs not to print the compile commands.
2225 By default, the commands that you specify with the
2226 \f[CB]\-XX:CompileCommand\f[R] option are printed; for example, if you
2227 exclude from compilation the \f[CB]indexOf()\f[R] method of the
2228 \f[CB]String\f[R] class, then the following is printed to standard output:
2229 .RS
2230 .RS
2231 .PP
2232 \f[CB]CompilerOracle:\ exclude\ java/lang/String.indexOf\f[R]
2233 .RE
2234 .PP
2235 You can suppress this by specifying the
2236 \f[CB]\-XX:CompileCommand=quiet\f[R] option before other
2237 \f[CB]\-XX:CompileCommand\f[R] options.
2238 .RE
2239 .RE
2240 .TP
2241 .B \f[CB]\-XX:CompileCommandFile=\f[R]\f[I]filename\f[R]
2242 Sets the file from which JIT compiler commands are read.
2243 By default, the \f[CB]\&.hotspot_compiler\f[R] file is used to store
2244 commands performed by the JIT compiler.
2245 .RS
2246 .PP
2247 Each line in the command file represents a command, a class name, and a
2248 method name for which the command is used.
2249 For example, this line prints assembly code for the \f[CB]toString()\f[R]
2250 method of the \f[CB]String\f[R] class:
2251 .RS
2252 .PP
2253 \f[CB]print\ java/lang/String\ toString\f[R]
2254 .RE
2255 .PP
2256 If you\[aq]re using commands for the JIT compiler to perform on methods,
2257 then see the \f[CB]\-XX:CompileCommand\f[R] option.
2258 .RE
2259 .TP
2260 .B \f[CB]\-XX:CompilerDirectivesFile=\f[R]\f[I]file\f[R]
2261 Adds directives from a file to the directives stack when a program
2262 starts.
2263 See \f[B]Compiler Control\f[R]
2264 [https://docs.oracle.com/en/java/javase/12/vm/compiler\-control1.html#GUID\-94AD8194\-786A\-4F19\-BFFF\-278F8E237F3A].
2265 .RS
2266 .PP
2267 The \f[CB]\-XX:CompilerDirectivesFile\f[R] option has to be used together
2268 with the \f[CB]\-XX:UnlockDiagnosticVMOptions\f[R] option that unlocks
2269 diagnostic JVM options.
2270 .RE
2271 .TP
2272 .B \f[CB]\-XX:+CompilerDirectivesPrint\f[R]
2273 Prints the directives stack when the program starts or when a new
2274 directive is added.
2275 .RS
2276 .PP
2277 The \f[CB]\-XX:+CompilerDirectivesPrint\f[R] option has to be used
2278 together with the \f[CB]\-XX:UnlockDiagnosticVMOptions\f[R] option that
2279 unlocks diagnostic JVM options.
2280 .RE
2281 .TP
2282 .B \f[CB]\-XX:CompileOnly=\f[R]\f[I]methods\f[R]
2283 Sets the list of methods (separated by commas) to which compilation
2284 should be restricted.
2285 Only the specified methods are compiled.
2286 Specify each method with the full class name (including the packages and
2287 subpackages).
2288 For example, to compile only the \f[CB]length()\f[R] method of the
2289 \f[CB]String\f[R] class and the \f[CB]size()\f[R] method of the
2290 \f[CB]List\f[R] class, use the following:
2291 .RS
2292 .RS
2293 .PP
2294 \f[CB]\-XX:CompileOnly=java/lang/String.length,java/util/List.size\f[R]
2295 .RE
2296 .PP
2297 Note that the full class name is specified, including all packages and
2298 subpackages separated by a slash (\f[CB]/\f[R]).
2299 For easier cut and paste operations, it\[aq]s also possible to use the
2300 method name format produced by the \f[CB]\-XX:+PrintCompilation\f[R] and
2301 \f[CB]\-XX:+LogCompilation\f[R] options:
2302 .RS
2303 .PP
2304 \f[CB]\-XX:CompileOnly=java.lang.String::length,java.util.List::size\f[R]
2305 .RE
2306 .PP
2307 Although wildcards aren\[aq]t supported, you can specify only the class
2308 or package name to compile all methods in that class or package, as well
2309 as specify just the method to compile methods with this name in any
2310 class:
2311 .IP
2312 .nf
2313 \f[CB]
2314 \-XX:CompileOnly=java/lang/String
2315 \-XX:CompileOnly=java/lang
2316 \-XX:CompileOnly=.length
2317 \f[R]
2318 .fi
2319 .RE
2320 .TP
2321 .B \f[CB]\-XX:CompileThreshold=\f[R]\f[I]invocations\f[R]
2322 Sets the number of interpreted method invocations before compilation.
2323 By default, in the server JVM, the JIT compiler performs 10,000
2324 interpreted method invocations to gather information for efficient
2325 compilation.
2326 For the client JVM, the default setting is 1,500 invocations.
2327 This option is ignored when tiered compilation is enabled; see the
2328 option \f[CB]\-XX:\-TieredCompilation\f[R].
2329 The following example shows how to set the number of interpreted method
2330 invocations to 5,000:
2331 .RS
2332 .RS
2333 .PP
2334 \f[CB]\-XX:CompileThreshold=5000\f[R]
2335 .RE
2336 .PP
2337 You can completely disable interpretation of Java methods before
2338 compilation by specifying the \f[CB]\-Xcomp\f[R] option.
2339 .RE
2340 .TP
2341 .B \f[CB]\-XX:CompileThresholdScaling=\f[R]\f[I]scale\f[R]
2342 Provides unified control of first compilation.
2343 This option controls when methods are first compiled for both the tiered
2344 and the nontiered modes of operation.
2345 The \f[CB]CompileThresholdScaling\f[R] option has an integer value between
2346 0 and +Inf and scales the thresholds corresponding to the current mode
2347 of operation (both tiered and nontiered).
2348 Setting \f[CB]CompileThresholdScaling\f[R] to a value less than 1.0
2349 results in earlier compilation while values greater than 1.0 delay
2350 compilation.
2351 Setting \f[CB]CompileThresholdScaling\f[R] to 0 is equivalent to disabling
2352 compilation.
2353 .RS
2354 .RE
2355 .TP
2356 .B \f[CB]\-XX:+DoEscapeAnalysis\f[R]
2357 Enables the use of escape analysis.
2358 This option is enabled by default.
2359 To disable the use of escape analysis, specify
2360 \f[CB]\-XX:\-DoEscapeAnalysis\f[R].
2361 Only the Java HotSpot Server VM supports this option.
2362 .RS
2363 .RE
2364 .TP
2365 .B \f[CB]\-XX:InitialCodeCacheSize=\f[R]\f[I]size\f[R]
2366 Sets the initial code cache size (in bytes).
2367 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
2368 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
2369 \f[CB]G\f[R] to indicate gigabytes.
2370 The default value is set to 500 KB.
2371 The initial code cache size shouldn\[aq]t be less than the system\[aq]s
2372 minimal memory page size.
2373 The following example shows how to set the initial code cache size to 32
2374 KB:
2375 .RS
2376 .RS
2377 .PP
2378 \f[CB]\-XX:InitialCodeCacheSize=32k\f[R]
2379 .RE
2380 .RE
2381 .TP
2382 .B \f[CB]\-XX:+Inline\f[R]
2383 Enables method inlining.
2384 This option is enabled by default to increase performance.
2385 To disable method inlining, specify \f[CB]\-XX:\-Inline\f[R].
2386 .RS
2387 .RE
2388 .TP
2389 .B \f[CB]\-XX:InlineSmallCode=\f[R]\f[I]size\f[R]
2390 Sets the maximum code size (in bytes) for compiled methods that should
2391 be inlined.
2392 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
2393 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
2394 \f[CB]G\f[R] to indicate gigabytes.
2395 Only compiled methods with the size smaller than the specified size is
2396 inlined.
2397 By default, the maximum code size is set to 1000 bytes:
2398 .RS
2399 .RS
2400 .PP
2401 \f[CB]\-XX:InlineSmallCode=1000\f[R]
2402 .RE
2403 .RE
2404 .TP
2405 .B \f[CB]\-XX:+LogCompilation\f[R]
2406 Enables logging of compilation activity to a file named
2407 \f[CB]hotspot.log\f[R] in the current working directory.
2408 You can specify a different log file path and name using the
2409 \f[CB]\-XX:LogFile\f[R] option.
2410 .RS
2411 .PP
2412 By default, this option is disabled and compilation activity isn\[aq]t
2413 logged.
2414 The \f[CB]\-XX:+LogCompilation\f[R] option has to be used together with
2415 the \f[CB]\-XX:UnlockDiagnosticVMOptions\f[R] option that unlocks
2416 diagnostic JVM options.
2417 .PP
2418 You can enable verbose diagnostic output with a message printed to the
2419 console every time a method is compiled by using the
2420 \f[CB]\-XX:+PrintCompilation\f[R] option.
2421 .RE
2422 .TP
2423 .B \f[CB]\-XX:MaxInlineSize=\f[R]\f[I]size\f[R]
2424 Sets the maximum bytecode size (in bytes) of a method to be inlined.
2425 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
2426 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
2427 \f[CB]G\f[R] to indicate gigabytes.
2428 By default, the maximum bytecode size is set to 35 bytes:
2429 .RS
2430 .RS
2431 .PP
2432 \f[CB]\-XX:MaxInlineSize=35\f[R]
2433 .RE
2434 .RE
2435 .TP
2436 .B \f[CB]\-XX:MaxNodeLimit=\f[R]\f[I]nodes\f[R]
2437 Sets the maximum number of nodes to be used during single method
2438 compilation.
2439 By default, the maximum number of nodes is set to 65,000:
2440 .RS
2441 .RS
2442 .PP
2443 \f[CB]\-XX:MaxNodeLimit=65000\f[R]
2444 .RE
2445 .RE
2446 .TP
2447 .B \f[CB]\-XX:NonNMethodCodeHeapSize=\f[R]\f[I]size\f[R]
2448 Sets the size in bytes of the code segment containing nonmethod code.
2449 .RS
2450 .PP
2451 A nonmethod code segment containing nonmethod code, such as compiler
2452 buffers and the bytecode interpreter.
2453 This code type stays in the code cache forever.
2454 This flag is used only if \f[CB]\-XX:SegmentedCodeCache\f[R] is enabled.
2455 .RE
2456 .TP
2457 .B \f[CB]\-XX:NonProfiledCodeHeapSize=\f[R]\f[I]size\f[R]
2458 Sets the size in bytes of the code segment containing nonprofiled
2459 methods.
2460 This flag is used only if \f[CB]\-XX:SegmentedCodeCache\f[R] is enabled.
2461 .RS
2462 .RE
2463 .TP
2464 .B \f[CB]\-XX:MaxTrivialSize=\f[R]\f[I]size\f[R]
2465 Sets the maximum bytecode size (in bytes) of a trivial method to be
2466 inlined.
2467 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
2468 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
2469 \f[CB]G\f[R] to indicate gigabytes.
2470 By default, the maximum bytecode size of a trivial method is set to 6
2471 bytes:
2472 .RS
2473 .RS
2474 .PP
2475 \f[CB]\-XX:MaxTrivialSize=6\f[R]
2476 .RE
2477 .RE
2478 .TP
2479 .B \f[CB]\-XX:+OptimizeStringConcat\f[R]
2480 Enables the optimization of \f[CB]String\f[R] concatenation operations.
2481 This option is enabled by default.
2482 To disable the optimization of \f[CB]String\f[R] concatenation operations,
2483 specify \f[CB]\-XX:\-OptimizeStringConcat\f[R].
2484 Only the Java HotSpot Server VM supports this option.
2485 .RS
2486 .RE
2487 .TP
2488 .B \f[CB]\-XX:+PrintAssembly\f[R]
2489 Enables printing of assembly code for bytecoded and native methods by
2490 using the external \f[CB]hsdis\-<arch>.so\f[R] or \f[CB]\&.dll\f[R] library.
2491 For 64\-bit VM on Windows, it\[aq]s \f[CB]hsdis\-amd64.dll\f[R].
2492 This lets you to see the generated code, which may help you to diagnose
2493 performance issues.
2494 .RS
2495 .PP
2496 By default, this option is disabled and assembly code isn\[aq]t printed.
2497 The \f[CB]\-XX:+PrintAssembly\f[R] option has to be used together with the
2498 \f[CB]\-XX:UnlockDiagnosticVMOptions\f[R] option that unlocks diagnostic
2499 JVM options.
2500 .RE
2501 .TP
2502 .B \f[CB]\-XX:ProfiledCodeHeapSize=\f[R]\f[I]size\f[R]
2503 Sets the size in bytes of the code segment containing profiled methods.
2504 This flag is used only if \f[CB]\-XX:SegmentedCodeCache\f[R] is enabled.
2505 .RS
2506 .RE
2507 .TP
2508 .B \f[CB]\-XX:+PrintCompilation\f[R]
2509 Enables verbose diagnostic output from the JVM by printing a message to
2510 the console every time a method is compiled.
2511 This lets you to see which methods actually get compiled.
2512 By default, this option is disabled and diagnostic output isn\[aq]t
2513 printed.
2514 .RS
2515 .PP
2516 You can also log compilation activity to a file by using the
2517 \f[CB]\-XX:+LogCompilation\f[R] option.
2518 .RE
2519 .TP
2520 .B \f[CB]\-XX:+PrintInlining\f[R]
2521 Enables printing of inlining decisions.
2522 This let\[aq]s you see which methods are getting inlined.
2523 .RS
2524 .PP
2525 By default, this option is disabled and inlining information isn\[aq]t
2526 printed.
2527 The \f[CB]\-XX:+PrintInlining\f[R] option has to be used together with the
2528 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R] option that unlocks diagnostic
2529 JVM options.
2530 .RE
2531 .TP
2532 .B \f[CB]\-XX:ReservedCodeCacheSize=\f[R]\f[I]size\f[R]
2533 Sets the maximum code cache size (in bytes) for JIT\-compiled code.
2534 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
2535 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
2536 \f[CB]G\f[R] to indicate gigabytes.
2537 The default maximum code cache size is 240 MB; if you disable tiered
2538 compilation with the option \f[CB]\-XX:\-TieredCompilation\f[R], then the
2539 default size is 48 MB.
2540 This option has a limit of 2 GB; otherwise, an error is generated.
2541 The maximum code cache size shouldn\[aq]t be less than the initial code
2542 cache size; see the option \f[CB]\-XX:InitialCodeCacheSize\f[R].
2543 .RS
2544 .RE
2545 .TP
2546 .B \f[CB]\-XX:RTMAbortRatio=\f[R]\f[I]abort_ratio\f[R]
2547 Specifies the RTM abort ratio is specified as a percentage (%) of all
2548 executed RTM transactions.
2549 If a number of aborted transactions becomes greater than this ratio,
2550 then the compiled code is deoptimized.
2551 This ratio is used when the \f[CB]\-XX:+UseRTMDeopt\f[R] option is
2552 enabled.
2553 The default value of this option is 50.
2554 This means that the compiled code is deoptimized if 50% of all
2555 transactions are aborted.
2556 .RS
2557 .RE
2558 .TP
2559 .B \f[CB]\-XX:RTMRetryCount=\f[R]\f[I]number_of_retries\f[R]
2560 Specifies the number of times that the RTM locking code is retried, when
2561 it is aborted or busy, before falling back to the normal locking
2562 mechanism.
2563 The default value for this option is 5.
2564 The \f[CB]\-XX:UseRTMLocking\f[R] option must be enabled.
2565 .RS
2566 .RE
2567 .TP
2568 .B \f[CB]\-XX:+SegmentedCodeCache\f[R]
2569 Enables segmentation of the code cache.
2570 Without the \f[CB]\-XX:+SegmentedCodeCache\f[R], the code cache consists
2571 of one large segment.
2572 With \f[CB]\-XX:+SegmentedCodeCache\f[R], we have separate segments for
2573 nonmethod, profiled method, and nonprofiled method code.
2574 These segments aren\[aq]t resized at runtime.
2575 The feature is enabled by default if tiered compilation is enabled
2576 (\f[CB]\-XX:+TieredCompilation\f[R] ) and
2577 \f[CB]\-XX:ReservedCodeCacheSize\f[R] >= 240 MB.
2578 The advantages are better control of the memory footprint, reduced code
2579 fragmentation, and better iTLB/iCache behavior due to improved locality.
2580 iTLB/iCache is a CPU\-specific term meaning Instruction Translation
2581 Lookaside Buffer (ITLB).
2582 ICache is an instruction cache in theCPU.
2583 The implementation of the code cache can be found in the file:
2584 \f[CB]/share/vm/code/codeCache.cpp\f[R].
2585 .RS
2586 .RE
2587 .TP
2588 .B \f[CB]\-XX:StartAggressiveSweepingAt=\f[R]\f[I]percent\f[R]
2589 Forces stack scanning of active methods to aggressively remove unused
2590 code when only the given percentage of the code cache is free.
2591 The default value is 10%.
2592 .RS
2593 .RE
2594 .TP
2595 .B \f[CB]\-XX:\-TieredCompilation\f[R]
2596 Disables the use of tiered compilation.
2597 By default, this option is enabled.
2598 Only the Java HotSpot Server VM supports this option.
2599 .RS
2600 .RE
2601 .TP
2602 .B \f[CB]\-XX:+UseAES\f[R]
2603 Enables hardware\-based AES intrinsics for Intel, AMD, and SPARC
2604 hardware.
2605 Intel Westmere (2010 and newer), AMD Bulldozer (2011 and newer), and
2606 SPARC (T4 and newer) are the supported hardware.
2607 The \f[CB]\-XX:+UseAES\f[R] is used in conjunction with UseAESIntrinsics.
2608 Flags that control intrinsics now require the option
2609 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R].
2610 .RS
2611 .RE
2612 .TP
2613 .B \f[CB]\-XX:+UseAESIntrinsics\f[R]
2614 Enables \f[CB]\-XX:+UseAES\f[R] and \f[CB]\-XX:+UseAESIntrinsics\f[R] flags
2615 by default and are supported only for the Java HotSpot Server VM.
2616 To disable hardware\-based AES intrinsics, specify
2617 \f[CB]\-XX:\-UseAES\ \-XX:\-UseAESIntrinsics\f[R].
2618 For example, to enable hardware AES, use the following flags:
2619 .RS
2620 .RS
2621 .PP
2622 \f[CB]\-XX:+UseAES\ \-XX:+UseAESIntrinsics\f[R]
2623 .RE
2624 .PP
2625 Flags that control intrinsics now require the option
2626 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R].
2627 To support UseAES and UseAESIntrinsics flags, use the \f[CB]\-server\f[R]
2628 option to select the Java HotSpot Server VM.
2629 These flags aren\[aq]t supported on Client VM.
2630 .RE
2631 .TP
2632 .B \f[CB]\-XX:+UseCMoveUnconditionally\f[R]
2633 Generates CMove (scalar and vector) instructions regardless of
2634 profitability analysis.
2635 .RS
2636 .RE
2637 .TP
2638 .B \f[CB]\-XX:+UseCodeCacheFlushing\f[R]
2639 Enables flushing of the code cache before shutting down the compiler.
2640 This option is enabled by default.
2641 To disable flushing of the code cache before shutting down the compiler,
2642 specify \f[CB]\-XX:\-UseCodeCacheFlushing\f[R].
2643 .RS
2644 .RE
2645 .TP
2646 .B \f[CB]\-XX:+UseCondCardMark\f[R]
2647 Enables checking if the card is already marked before updating the card
2648 table.
2649 This option is disabled by default.
2650 It should be used only on machines with multiple sockets, where it
2651 increases the performance of Java applications that rely on concurrent
2652 operations.
2653 Only the Java HotSpot Server VM supports this option.
2654 .RS
2655 .RE
2656 .TP
2657 .B \f[CB]\-XX:+UseCountedLoopSafepoints\f[R]
2658 Keeps safepoints in counted loops.
2659 Its default value is false.\
2660 .RS
2661 .RE
2662 .TP
2663 .B \f[CB]\-XX:+UseFMA\f[R]
2664 Enables hardware\-based FMA intrinsics for hardware where FMA
2665 instructions are available (such as, Intel, SPARC, and ARM64).
2666 FMA intrinsics are generated for the
2667 \f[CB]java.lang.Math.fma(\f[R]\f[I]a\f[R]\f[CB],\f[R] \f[I]b\f[R]\f[CB],\f[R]
2668 \f[I]c\f[R]\f[CB])\f[R] methods that calculate the value of \f[CB](\f[R]
2669 \f[I]a\f[R] \f[CB]*\f[R] \f[I]b\f[R] \f[CB]+\f[R] \f[I]c\f[R] \f[CB])\f[R]
2670 expressions.
2671 .RS
2672 .RE
2673 .TP
2674 .B \f[CB]\-XX:+UseRTMDeopt\f[R]
2675 Autotunes RTM locking depending on the abort ratio.
2676 This ratio is specified by the \f[CB]\-XX:RTMAbortRatio\f[R] option.
2677 If the number of aborted transactions exceeds the abort ratio, then the
2678 method containing the lock is deoptimized and recompiled with all locks
2679 as normal locks.
2680 This option is disabled by default.
2681 The \f[CB]\-XX:+UseRTMLocking\f[R] option must be enabled.
2682 .RS
2683 .RE
2684 .TP
2685 .B \f[CB]\-XX:+UseRTMLocking\f[R]
2686 Generates Restricted Transactional Memory (RTM) locking code for all
2687 inflated locks, with the normal locking mechanism as the fallback
2688 handler.
2689 This option is disabled by default.
2690 Options related to RTM are available only for the Java HotSpot Server VM
2691 on x86 CPUs that support Transactional Synchronization Extensions (TSX).
2692 .RS
2693 .PP
2694 RTM is part of Intel\[aq]s TSX, which is an x86 instruction set
2695 extension and facilitates the creation of multithreaded applications.
2696 RTM introduces the new instructions \f[CB]XBEGIN\f[R], \f[CB]XABORT\f[R],
2697 \f[CB]XEND\f[R], and \f[CB]XTEST\f[R].
2698 The \f[CB]XBEGIN\f[R] and \f[CB]XEND\f[R] instructions enclose a set of
2699 instructions to run as a transaction.
2700 If no conflict is found when running the transaction, then the memory
2701 and register modifications are committed together at the \f[CB]XEND\f[R]
2702 instruction.
2703 The \f[CB]XABORT\f[R] instruction can be used to explicitly abort a
2704 transaction and the \f[CB]XEND\f[R] instruction checks if a set of
2705 instructions is being run in a transaction.
2706 .PP
2707 A lock on a transaction is inflated when another thread tries to access
2708 the same transaction, thereby blocking the thread that didn\[aq]t
2709 originally request access to the transaction.
2710 RTM requires that a fallback set of operations be specified in case a
2711 transaction aborts or fails.
2712 An RTM lock is a lock that has been delegated to the TSX\[aq]s system.
2713 .PP
2714 RTM improves performance for highly contended locks with low conflict in
2715 a critical region (which is code that must not be accessed by more than
2716 one thread concurrently).
2717 RTM also improves the performance of coarse\-grain locking, which
2718 typically doesn\[aq]t perform well in multithreaded applications.
2719 (Coarse\-grain locking is the strategy of holding locks for long periods
2720 to minimize the overhead of taking and releasing locks, while
2721 fine\-grained locking is the strategy of trying to achieve maximum
2722 parallelism by locking only when necessary and unlocking as soon as
2723 possible.) Also, for lightly contended locks that are used by different
2724 threads, RTM can reduce false cache line sharing, also known as cache
2725 line ping\-pong.
2726 This occurs when multiple threads from different processors are
2727 accessing different resources, but the resources share the same cache
2728 line.
2729 As a result, the processors repeatedly invalidate the cache lines of
2730 other processors, which forces them to read from main memory instead of
2731 their cache.
2732 .RE
2733 .TP
2734 .B \f[CB]\-XX:+UseSHA\f[R]
2735 Enables hardware\-based intrinsics for SHA crypto hash functions for
2736 SPARC hardware.
2737 The \f[CB]UseSHA\f[R] option is used in conjunction with the
2738 \f[CB]UseSHA1Intrinsics\f[R], \f[CB]UseSHA256Intrinsics\f[R], and
2739 \f[CB]UseSHA512Intrinsics\f[R] options.
2740 .RS
2741 .PP
2742 The \f[CB]UseSHA\f[R] and \f[CB]UseSHA*Intrinsics\f[R] flags are enabled by
2743 default, and are supported only for Java HotSpot Server VM 64\-bit on
2744 SPARC T4 and newer.
2745 .PP
2746 This feature is applicable only when using the
2747 \f[CB]sun.security.provider.Sun\f[R] provider for SHA operations.
2748 Flags that control intrinsics now require the option
2749 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R].
2750 .PP
2751 To disable all hardware\-based SHA intrinsics, specify the
2752 \f[CB]\-XX:\-UseSHA\f[R].
2753 To disable only a particular SHA intrinsic, use the appropriate
2754 corresponding option.
2755 For example: \f[CB]\-XX:\-UseSHA256Intrinsics\f[R].
2756 .RE
2757 .TP
2758 .B \f[CB]\-XX:+UseSHA1Intrinsics\f[R]
2759 Enables intrinsics for SHA\-1 crypto hash function.
2760 Flags that control intrinsics now require the option
2761 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R].
2762 .RS
2763 .RE
2764 .TP
2765 .B \f[CB]\-XX:+UseSHA256Intrinsics\f[R]
2766 Enables intrinsics for SHA\-224 and SHA\-256 crypto hash functions.
2767 Flags that control intrinsics now require the option
2768 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R].
2769 .RS
2770 .RE
2771 .TP
2772 .B \f[CB]\-XX:+UseSHA512Intrinsics\f[R]
2773 Enables intrinsics for SHA\-384 and SHA\-512 crypto hash functions.
2774 Flags that control intrinsics now require the option
2775 \f[CB]\-XX:+UnlockDiagnosticVMOptions\f[R].
2776 .RS
2777 .RE
2778 .TP
2779 .B \f[CB]\-XX:+UseSuperWord\f[R]
2780 Enables the transformation of scalar operations into superword
2781 operations.
2782 Superword is a vectorization optimization.
2783 This option is enabled by default.
2784 To disable the transformation of scalar operations into superword
2785 operations, specify \f[CB]\-XX:\-UseSuperWord\f[R].
2786 Only the Java HotSpot Server VM supports this option.
2787 .RS
2788 .RE
2789 .SH ADVANCED SERVICEABILITY OPTIONS FOR JAVA
2790 .PP
2791 These \f[CB]java\f[R] options provide the ability to gather system
2792 information and perform extensive debugging.
2793 .TP
2794 .B \f[CB]\-XX:+DisableAttachMechanism\f[R]
2795 Disables the mechanism that lets tools attach to the JVM.
2796 By default, this option is disabled, meaning that the attach mechanism
2797 is enabled and you can use diagnostics and troubleshooting tools such as
2798 \f[CB]jcmd\f[R], \f[CB]jstack\f[R], \f[CB]jmap\f[R], and \f[CB]jinfo\f[R].
2799 .RS
2800 .RS
2801 .PP
2802 \f[B]Note:\f[R] The tools such as \f[B]jcmd\f[R], \f[B]jinfo\f[R],
2803 \f[B]jmap\f[R], and \f[B]jstack\f[R] shipped with the JDK aren\[aq]t
2804 supported when using the tools from one JDK version to troubleshoot a
2805 different JDK version.
2806 .RE
2807 .RE
2808 .TP
2809 .B \f[CB]\-XX:+ExtendedDTraceProbes\f[R]
2810 \f[B]Oracle Solaris, Linux, and macOS:\f[R] Enables additional
2811 \f[CB]dtrace\f[R] tool probes that affect the performance.
2812 By default, this option is disabled and \f[CB]dtrace\f[R] performs only
2813 standard probes.
2814 .RS
2815 .RE
2816 .TP
2817 .B \f[CB]\-XX:+HeapDumpOnOutOfMemoryError\f[R]
2818 Enables the dumping of the Java heap to a file in the current directory
2819 by using the heap profiler (HPROF) when a
2820 \f[CB]java.lang.OutOfMemoryError\f[R] exception is thrown.
2821 You can explicitly set the heap dump file path and name using the
2822 \f[CB]\-XX:HeapDumpPath\f[R] option.
2823 By default, this option is disabled and the heap isn\[aq]t dumped when
2824 an \f[CB]OutOfMemoryError\f[R] exception is thrown.
2825 .RS
2826 .RE
2827 .TP
2828 .B \f[CB]\-XX:HeapDumpPath=path\f[R]
2829 Sets the path and file name for writing the heap dump provided by the
2830 heap profiler (HPROF) when the \f[CB]\-XX:+HeapDumpOnOutOfMemoryError\f[R]
2831 option is set.
2832 By default, the file is created in the current working directory, and
2833 it\[aq]s named \f[CB]java_pid<pid>.hprof\f[R] where \f[CB]<pid>\f[R] is the
2834 identifier of the process that caused the error.
2835 The following example shows how to set the default file explicitly
2836 (\f[CB]%p\f[R] represents the current process identifier):
2837 .RS
2838 .RS
2839 .PP
2840 \f[CB]\-XX:HeapDumpPath=./java_pid%p.hprof\f[R]
2841 .RE
2842 .IP \[bu] 2
2843 \f[B]Oracle Solaris, Linux, and macOS:\f[R] The following example shows
2844 how to set the heap dump file to
2845 \f[CB]/var/log/java/java_heapdump.hprof\f[R]:
2846 .RS 2
2847 .RS
2848 .PP
2849 \f[CB]\-XX:HeapDumpPath=/var/log/java/java_heapdump.hprof\f[R]
2850 .RE
2851 .RE
2852 .IP \[bu] 2
2853 \f[B]Windows:\f[R] The following example shows how to set the heap dump
2854 file to \f[CB]C:/log/java/java_heapdump.log\f[R]:
2855 .RS 2
2856 .RS
2857 .PP
2858 \f[CB]\-XX:HeapDumpPath=C:/log/java/java_heapdump.log\f[R]
2859 .RE
2860 .RE
2861 .RE
2862 .TP
2863 .B \f[CB]\-XX:LogFile=\f[R]\f[I]path\f[R]
2864 Sets the path and file name to where log data is written.
2865 By default, the file is created in the current working directory, and
2866 it\[aq]s named \f[CB]hotspot.log\f[R].
2867 .RS
2868 .IP \[bu] 2
2869 \f[B]Oracle Solaris, Linux, and macOS:\f[R] The following example shows
2870 how to set the log file to \f[CB]/var/log/java/hotspot.log\f[R]:
2871 .RS 2
2872 .RS
2873 .PP
2874 \f[CB]\-XX:LogFile=/var/log/java/hotspot.log\f[R]
2875 .RE
2876 .RE
2877 .IP \[bu] 2
2878 \f[B]Windows:\f[R] The following example shows how to set the log file to
2879 \f[CB]C:/log/java/hotspot.log\f[R]:
2880 .RS 2
2881 .RS
2882 .PP
2883 \f[CB]\-XX:LogFile=C:/log/java/hotspot.log\f[R]
2884 .RE
2885 .RE
2886 .RE
2887 .TP
2888 .B \f[CB]\-XX:+PrintClassHistogram\f[R]
2889 Enables printing of a class instance histogram after one of the
2890 following events:
2891 .RS
2892 .IP \[bu] 2
2893 \f[B]Oracle Solaris, Linux, and macOS:\f[R] \f[CB]Control+Break\f[R]
2894 .IP \[bu] 2
2895 \f[B]Windows:\f[R] \f[CB]Control+C\f[R] (\f[CB]SIGTERM\f[R])
2896 .PP
2897 By default, this option is disabled.
2898 .PP
2899 Setting this option is equivalent to running the \f[CB]jmap\ \-histo\f[R]
2900 command, or the \f[CB]jcmd\f[R] \f[I]pid\f[R] \f[CB]GC.class_histogram\f[R]
2901 command, where \f[I]pid\f[R] is the current Java process identifier.
2902 .RE
2903 .TP
2904 .B \f[CB]\-XX:+PrintConcurrentLocks\f[R]
2905 Enables printing of \f[CB]java.util.concurrent\f[R] locks after one of the
2906 following events:
2907 .RS
2908 .IP \[bu] 2
2909 \f[B]Oracle Solaris, Linux, and macOS:\f[R] \f[CB]Control+Break\f[R]
2910 .IP \[bu] 2
2911 \f[B]Windows:\f[R] \f[CB]Control+C\f[R] (\f[CB]SIGTERM\f[R])
2912 .PP
2913 By default, this option is disabled.
2914 .PP
2915 Setting this option is equivalent to running the \f[CB]jstack\ \-l\f[R]
2916 command or the \f[CB]jcmd\f[R] \f[I]pid\f[R] \f[CB]Thread.print\ \-l\f[R]
2917 command, where \f[I]pid\f[R] is the current Java process identifier.
2918 .RE
2919 .TP
2920 .B \f[CB]\-XX:+PrintFlagsRanges\f[R]
2921 Prints the range specified and allows automatic testing of the values.
2922 See \f[B]Validate Java Virtual Machine Flag Arguments\f[R].
2923 .RS
2924 .RE
2925 .TP
2926 .B \f[CB]\-XX:+PerfDataSaveToFile\f[R]
2927 If enabled, saves \f[B]jstat\f[R] binary data when the Java application
2928 exits.
2929 This binary data is saved in a file named
2930 \f[CB]hsperfdata_\f[R]\f[I]pid\f[R], where \f[I]pid\f[R] is the process
2931 identifier of the Java application that you ran.
2932 Use the \f[CB]jstat\f[R] command to display the performance data contained
2933 in this file as follows:
2934 .RS
2935 .RS
2936 .PP
2937 \f[CB]jstat\ \-class\ file:///\f[R]\f[I]path\f[R]\f[CB]/hsperfdata_\f[R]\f[I]pid\f[R]
2938 .RE
2939 .RS
2940 .PP
2941 \f[CB]jstat\ \-gc\ file:///\f[R]\f[I]path\f[R]\f[CB]/hsperfdata_\f[R]\f[I]pid\f[R]
2942 .RE
2943 .RE
2944 .TP
2945 .B \f[CB]\-XX:+UsePerfData\f[R]
2946 Enables the \f[CB]perfdata\f[R] feature.
2947 This option is enabled by default to allow JVM monitoring and
2948 performance testing.
2949 Disabling it suppresses the creation of the \f[CB]hsperfdata_userid\f[R]
2950 directories.
2951 To disable the \f[CB]perfdata\f[R] feature, specify
2952 \f[CB]\-XX:\-UsePerfData\f[R].
2953 .RS
2954 .RE
2955 .SH ADVANCED GARBAGE COLLECTION OPTIONS FOR JAVA
2956 .PP
2957 These \f[CB]java\f[R] options control how garbage collection (GC) is
2958 performed by the Java HotSpot VM.
2959 .TP
2960 .B \f[CB]\-XX:+AggressiveHeap\f[R]
2961 Enables Java heap optimization.
2962 This sets various parameters to be optimal for long\-running jobs with
2963 intensive memory allocation, based on the configuration of the computer
2964 (RAM and CPU).
2965 By default, the option is disabled and the heap sizes are configured
2966 less aggressively.
2967 .RS
2968 .RE
2969 .TP
2970 .B \f[CB]\-XX:+AlwaysPreTouch\f[R]
2971 Requests the VM to touch every page on the Java heap after requesting it
2972 from the operating system and before handing memory out to the
2973 application.
2974 By default, this option is disabled and all pages are committed as the
2975 application uses the heap space.
2976 .RS
2977 .RE
2978 .TP
2979 .B \f[CB]\-XX:+CMSClassUnloadingEnabled\f[R]
2980 Enables class unloading when using the concurrent mark\-sweep (CMS)
2981 garbage collector.
2982 This option is enabled by default.
2983 To disable class unloading for the CMS garbage collector, specify
2984 \f[CB]\-XX:\-CMSClassUnloadingEnabled\f[R].
2985 .RS
2986 .RE
2987 .TP
2988 .B \f[CB]\-XX:CMSExpAvgFactor=\f[R]\f[I]percent\f[R]
2989 Sets the percentage of time (0 to 100) used to weight the current sample
2990 when computing exponential averages for the concurrent collection
2991 statistics.
2992 By default, the exponential averages factor is set to 25%.
2993 The following example shows how to set the factor to 15%:
2994 .RS
2995 .RS
2996 .PP
2997 \f[CB]\-XX:CMSExpAvgFactor=15\f[R]
2998 .RE
2999 .RE
3000 .TP
3001 .B \f[CB]\-XX:CMSInitiatingOccupancyFraction=\f[R]\f[I]percent\f[R]
3002 Sets the percentage of the old generation occupancy (0 to 100) at which
3003 to start a CMS collection cycle.
3004 The default value is set to \-1.
3005 Any negative value (including the default) implies that the option
3006 \f[CB]\-XX:CMSTriggerRatio\f[R] is used to define the value of the
3007 initiating occupancy fraction.
3008 .RS
3009 .PP
3010 The following example shows how to set the factor to 20%:
3011 .RS
3012 .PP
3013 \f[CB]\-XX:CMSInitiatingOccupancyFraction=20\f[R]
3014 .RE
3015 .RE
3016 .TP
3017 .B \f[CB]\-XX:CMSIncrementalDutySafetyFactor=\f[R]\f[I]percent\f[R]
3018 Sets the percentage (0 to 100) used to add conservatism when computing
3019 the duty cycle.
3020 The default value is 10.
3021 .RS
3022 .RE
3023 .TP
3024 .B \f[CB]\-XX:+CMSScavengeBeforeRemark\f[R]
3025 Enables scavenging attempts before the CMS remark step.
3026 By default, this option is disabled.
3027 .RS
3028 .RE
3029 .TP
3030 .B \f[CB]\-XX:CMSTriggerRatio=percent\f[R]
3031 Sets the percentage (0 to 100) of the value specified by the option
3032 \f[CB]\-XX:MinHeapFreeRatio\f[R] that\[aq]s allocated before a CMS
3033 collection cycle commences.
3034 The default value is set to 80%.
3035 .RS
3036 .PP
3037 The following example shows how to set the occupancy fraction to 75%:
3038 .RS
3039 .PP
3040 \f[CB]\-XX:CMSTriggerRatio=75\f[R]
3041 .RE
3042 .RE
3043 .TP
3044 .B \f[CB]\-XX:ConcGCThreads=\f[R]\f[I]threads\f[R]
3045 Sets the number of threads used for concurrent GC.
3046 Sets \f[I]\f[CI]threads\f[I]\f[R] to approximately 1/4 of the number of
3047 parallel garbage collection threads.
3048 The default value depends on the number of CPUs available to the JVM.
3049 .RS
3050 .PP
3051 For example, to set the number of threads for concurrent GC to 2,
3052 specify the following option:
3053 .RS
3054 .PP
3055 \f[CB]\-XX:ConcGCThreads=2\f[R]
3056 .RE
3057 .RE
3058 .TP
3059 .B \f[CB]\-XX:+DisableExplicitGC\f[R]
3060 Enables the option that disables processing of calls to the
3061 \f[CB]System.gc()\f[R] method.
3062 This option is disabled by default, meaning that calls to
3063 \f[CB]System.gc()\f[R] are processed.
3064 If processing of calls to \f[CB]System.gc()\f[R] is disabled, then the JVM
3065 still performs GC when necessary.
3066 .RS
3067 .RE
3068 .TP
3069 .B \f[CB]\-XX:+ExplicitGCInvokesConcurrent\f[R]
3070 Enables invoking of concurrent GC by using the \f[CB]System.gc()\f[R]
3071 request.
3072 This option is disabled by default and can be enabled only with the
3073 deprecated \f[CB]\-XX:+UseConcMarkSweepGC\f[R] option and the
3074 \f[CB]\-XX:+UseG1GC\f[R] option.
3075 .RS
3076 .RE
3077 .TP
3078 .B \f[CB]\-XX:G1AdaptiveIHOPNumInitialSamples=\f[R]\f[I]number\f[R]
3079 When \f[CB]\-XX:UseAdaptiveIHOP\f[R] is enabled, this option sets the
3080 number of completed marking cycles used to gather samples until G1
3081 adaptively determines the optimum value of
3082 \f[CB]\-XX:InitiatingHeapOccupancyPercent\f[R].
3083 Before, G1 uses the value of
3084 \f[CB]\-XX:InitiatingHeapOccupancyPercent\f[R] directly for this purpose.
3085 The default value is 3.
3086 .RS
3087 .RE
3088 .TP
3089 .B \f[CB]\-XX:G1HeapRegionSize=size\f[R]
3090 Sets the size of the regions into which the Java heap is subdivided when
3091 using the garbage\-first (G1) collector.
3092 The value is a power of 2 and can range from 1 MB to 32 MB.
3093 The default region size is determined ergonomically based on the heap
3094 size with a goal of approximately 2048 regions.
3095 .RS
3096 .PP
3097 The following example sets the size of the subdivisions to 16 MB:
3098 .RS
3099 .PP
3100 \f[CB]\-XX:G1HeapRegionSize=16m\f[R]
3101 .RE
3102 .RE
3103 .TP
3104 .B \f[CB]\-XX:G1HeapWastePercent=\f[R]\f[I]percent\f[R]
3105 Sets the percentage of heap that you\[aq]re willing to waste.
3106 The Java HotSpot VM doesn\[aq]t initiate the mixed garbage collection
3107 cycle when the reclaimable percentage is less than the heap waste
3108 percentage.
3109 The default is 5 percent.
3110 .RS
3111 .RE
3112 .TP
3113 .B \f[CB]\-XX:G1MaxNewSizePercent=\f[R]\f[I]percent\f[R]
3114 Sets the percentage of the heap size to use as the maximum for the young
3115 generation size.
3116 The default value is 60 percent of your Java heap.
3117 .RS
3118 .PP
3119 This is an experimental flag.
3120 This setting replaces the \f[CB]\-XX:DefaultMaxNewGenPercent\f[R] setting.
3121 .RE
3122 .TP
3123 .B \f[CB]\-XX:G1MixedGCCountTarget=\f[R]\f[I]number\f[R]
3124 Sets the target number of mixed garbage collections after a marking
3125 cycle to collect old regions with at most
3126 \f[CB]G1MixedGCLIveThresholdPercent\f[R] live data.
3127 The default is 8 mixed garbage collections.
3128 The goal for mixed collections is to be within this target number.
3129 .RS
3130 .RE
3131 .TP
3132 .B \f[CB]\-XX:G1MixedGCLiveThresholdPercent=\f[R]\f[I]percent\f[R]
3133 Sets the occupancy threshold for an old region to be included in a mixed
3134 garbage collection cycle.
3135 The default occupancy is 85 percent.
3136 .RS
3137 .PP
3138 This is an experimental flag.
3139 This setting replaces the
3140 \f[CB]\-XX:G1OldCSetRegionLiveThresholdPercent\f[R] setting.
3141 .RE
3142 .TP
3143 .B \f[CB]\-XX:G1NewSizePercent=\f[R]\f[I]percent\f[R]
3144 Sets the percentage of the heap to use as the minimum for the young
3145 generation size.
3146 The default value is 5 percent of your Java heap.
3147 .RS
3148 .PP
3149 This is an experimental flag.
3150 This setting replaces the \f[CB]\-XX:DefaultMinNewGenPercent\f[R] setting.
3151 .RE
3152 .TP
3153 .B \f[CB]\-XX:G1OldCSetRegionThresholdPercent=\f[R]\f[I]percent\f[R]
3154 Sets an upper limit on the number of old regions to be collected during
3155 a mixed garbage collection cycle.
3156 The default is 10 percent of the Java heap.
3157 .RS
3158 .RE
3159 .TP
3160 .B \f[CB]\-XX:G1ReservePercent=\f[R]\f[I]percent\f[R]
3161 Sets the percentage of the heap (0 to 50) that\[aq]s reserved as a false
3162 ceiling to reduce the possibility of promotion failure for the G1
3163 collector.
3164 When you increase or decrease the percentage, ensure that you adjust the
3165 total Java heap by the same amount.
3166 By default, this option is set to 10%.
3167 .RS
3168 .PP
3169 The following example sets the reserved heap to 20%:
3170 .RS
3171 .PP
3172 \f[CB]\-XX:G1ReservePercent=20\f[R]
3173 .RE
3174 .RE
3175 .TP
3176 .B \f[CB]\-XX:+G1UseAdaptiveIHOP\f[R]
3177 Controls adaptive calculation of the old generation occupancy to start
3178 background work preparing for an old generation collection.
3179 If enabled, G1 uses \f[CB]\-XX:InitiatingHeapOccupancyPercent\f[R] for the
3180 first few times as specified by the value of
3181 \f[CB]\-XX:G1AdaptiveIHOPNumInitialSamples\f[R], and after that adaptively
3182 calculates a new optimum value for the initiating occupancy
3183 automatically.
3184 Otherwise, the old generation collection process always starts at the
3185 old generation occupancy determined by
3186 \f[CB]\-XX:InitiatingHeapOccupancyPercent\f[R].
3187 .RS
3188 .PP
3189 The default is enabled.
3190 .RE
3191 .TP
3192 .B \f[CB]\-XX:InitialHeapSize=\f[R]\f[I]size\f[R]
3193 Sets the initial size (in bytes) of the memory allocation pool.
3194 This value must be either 0, or a multiple of 1024 and greater than 1
3195 MB.
3196 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
3197 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
3198 \f[CB]G\f[R] to indicate gigabytes.
3199 The default value is selected at run time based on the system
3200 configuration.
3201 .RS
3202 .PP
3203 The following examples show how to set the size of allocated memory to 6
3204 MB using various units:
3205 .IP
3206 .nf
3207 \f[CB]
3208 \-XX:InitialHeapSize=6291456
3209 \-XX:InitialHeapSize=6144k
3210 \-XX:InitialHeapSize=6m
3211 \f[R]
3212 .fi
3213 .PP
3214 If you set this option to 0, then the initial size is set as the sum of
3215 the sizes allocated for the old generation and the young generation.
3216 The size of the heap for the young generation can be set using the
3217 \f[CB]\-XX:NewSize\f[R] option.
3218 .RE
3219 .TP
3220 .B \f[CB]\-XX:InitialRAMPercentage=\f[R]\f[I]percent\f[R]
3221 Sets the initial amount of memory that the JVM will use for the Java
3222 heap before applying ergonomics heuristics as a percentage of the
3223 maximum amount determined as described in the \f[CB]\-XX:MaxRAM\f[R]
3224 option.
3225 The default value is 1.5625 percent.
3226 .RS
3227 .PP
3228 The following example shows how to set the percentage of the initial
3229 amount of memory used for the Java heap:
3230 .RS
3231 .PP
3232 \f[CB]\-XX:InitialRAMPercentage=5\f[R]
3233 .RE
3234 .RE
3235 .TP
3236 .B \f[CB]\-XX:InitialSurvivorRatio=\f[R]\f[I]ratio\f[R]
3237 Sets the initial survivor space ratio used by the throughput garbage
3238 collector (which is enabled by the \f[CB]\-XX:+UseParallelGC\f[R] and/or
3239 \f[CB]\-XX:+UseParallelOldGC\f[R] options).
3240 Adaptive sizing is enabled by default with the throughput garbage
3241 collector by using the \f[CB]\-XX:+UseParallelGC\f[R] and
3242 \f[CB]\-XX:+UseParallelOldGC\f[R] options, and the survivor space is
3243 resized according to the application behavior, starting with the initial
3244 value.
3245 If adaptive sizing is disabled (using the
3246 \f[CB]\-XX:\-UseAdaptiveSizePolicy\f[R] option), then the
3247 \f[CB]\-XX:SurvivorRatio\f[R] option should be used to set the size of the
3248 survivor space for the entire execution of the application.
3249 .RS
3250 .PP
3251 The following formula can be used to calculate the initial size of
3252 survivor space (S) based on the size of the young generation (Y), and
3253 the initial survivor space ratio (R):
3254 .RS
3255 .PP
3256 \f[CB]S=Y/(R+2)\f[R]
3257 .RE
3258 .PP
3259 The 2 in the equation denotes two survivor spaces.
3260 The larger the value specified as the initial survivor space ratio, the
3261 smaller the initial survivor space size.
3262 .PP
3263 By default, the initial survivor space ratio is set to 8.
3264 If the default value for the young generation space size is used (2 MB),
3265 then the initial size of the survivor space is 0.2 MB.
3266 .PP
3267 The following example shows how to set the initial survivor space ratio
3268 to 4:
3269 .RS
3270 .PP
3271 \f[CB]\-XX:InitialSurvivorRatio=4\f[R]
3272 .RE
3273 .RE
3274 .TP
3275 .B \f[CB]\-XX:InitiatingHeapOccupancyPercent=\f[R]\f[I]percent\f[R]
3276 Sets the percentage of the old generation occupancy (0 to 100) at which
3277 to start the first few concurrent marking cycles for the G1 garbage
3278 collector.
3279 .RS
3280 .PP
3281 By default, the initiating value is set to 45%.
3282 A value of 0 implies nonstop concurrent GC cycles from the beginning
3283 until G1 adaptively sets this value.
3284 .PP
3285 See also the \f[CB]\-XX:G1UseAdaptiveIHOP\f[R] and
3286 \f[CB]\-XX:G1AdaptiveIHOPNumInitialSamples\f[R] options.
3287 .PP
3288 The following example shows how to set the initiating heap occupancy to
3289 75%:
3290 .RS
3291 .PP
3292 \f[CB]\-XX:InitiatingHeapOccupancyPercent=75\f[R]
3293 .RE
3294 .RE
3295 .TP
3296 .B \f[CB]\-XX:MaxGCPauseMillis=\f[R]\f[I]time\f[R]
3297 Sets a target for the maximum GC pause time (in milliseconds).
3298 This is a soft goal, and the JVM will make its best effort to achieve
3299 it.
3300 The specified value doesn\[aq]t adapt to your heap size.
3301 By default, for G1 the maximum pause time target is 200 milliseconds.
3302 The other generational collectors do not use a pause time goal by
3303 default.
3304 .RS
3305 .PP
3306 The following example shows how to set the maximum target pause time to
3307 500 ms:
3308 .RS
3309 .PP
3310 \f[CB]\-XX:MaxGCPauseMillis=500\f[R]
3311 .RE
3312 .RE
3313 .TP
3314 .B \f[CB]\-XX:MaxHeapSize=\f[R]\f[I]size\f[R]
3315 Sets the maximum size (in byes) of the memory allocation pool.
3316 This value must be a multiple of 1024 and greater than 2 MB.
3317 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
3318 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
3319 \f[CB]G\f[R] to indicate gigabytes.
3320 The default value is selected at run time based on the system
3321 configuration.
3322 For server deployments, the options \f[CB]\-XX:InitialHeapSize\f[R] and
3323 \f[CB]\-XX:MaxHeapSize\f[R] are often set to the same value.
3324 .RS
3325 .PP
3326 The following examples show how to set the maximum allowed size of
3327 allocated memory to 80 MB using various units:
3328 .IP
3329 .nf
3330 \f[CB]
3331 \-XX:MaxHeapSize=83886080
3332 \-XX:MaxHeapSize=81920k
3333 \-XX:MaxHeapSize=80m
3334 \f[R]
3335 .fi
3336 .PP
3337 The \f[CB]\-XX:MaxHeapSize\f[R] option is equivalent to \f[CB]\-Xmx\f[R].
3338 .RE
3339 .TP
3340 .B \f[CB]\-XX:MaxHeapFreeRatio=\f[R]\f[I]percent\f[R]
3341 Sets the maximum allowed percentage of free heap space (0 to 100) after
3342 a GC event.
3343 If free heap space expands above this value, then the heap is shrunk.
3344 By default, this value is set to 70%.
3345 .RS
3346 .PP
3347 Minimize the Java heap size by lowering the values of the parameters
3348 \f[CB]MaxHeapFreeRatio\f[R] (default value is 70%) and
3349 \f[CB]MinHeapFreeRatio\f[R] (default value is 40%) with the command\-line
3350 options \f[CB]\-XX:MaxHeapFreeRatio\f[R] and
3351 \f[CB]\-XX:MinHeapFreeRatio\f[R].
3352 Lowering \f[CB]MaxHeapFreeRatio\f[R] to as low as 10% and
3353 \f[CB]MinHeapFreeRatio\f[R] to 5% has successfully reduced the heap size
3354 without too much performance regression; however, results may vary
3355 greatly depending on your application.
3356 Try different values for these parameters until they\[aq]re as low as
3357 possible yet still retain acceptable performance.
3358 .RS
3359 .PP
3360 \f[CB]\-XX:MaxHeapFreeRatio=10\ \-XX:MinHeapFreeRatio=5\f[R]
3361 .RE
3362 .PP
3363 Customers trying to keep the heap small should also add the option
3364 \f[CB]\-XX:\-ShrinkHeapInSteps\f[R].
3365 See \f[B]Performance Tuning Examples\f[R] for a description of using this
3366 option to keep the Java heap small by reducing the dynamic footprint for
3367 embedded applications.
3368 .RE
3369 .TP
3370 .B \f[CB]\-XX:MaxMetaspaceSize=\f[R]\f[I]size\f[R]
3371 Sets the maximum amount of native memory that can be allocated for class
3372 metadata.
3373 By default, the size isn\[aq]t limited.
3374 The amount of metadata for an application depends on the application
3375 itself, other running applications, and the amount of memory available
3376 on the system.
3377 .RS
3378 .PP
3379 The following example shows how to set the maximum class metadata size
3380 to 256 MB:
3381 .RS
3382 .PP
3383 \f[CB]\-XX:MaxMetaspaceSize=256m\f[R]
3384 .RE
3385 .RE
3386 .TP
3387 .B \f[CB]\-XX:MaxNewSize=\f[R]\f[I]size\f[R]
3388 Sets the maximum size (in bytes) of the heap for the young generation
3389 (nursery).
3390 The default value is set ergonomically.
3391 .RS
3392 .RE
3393 .TP
3394 .B \f[CB]\-XX:MaxRAM=\f[R]\f[I]size\f[R]
3395 Sets the maximum amount of memory that the JVM may use for the Java heap
3396 before applying ergonomics heuristics.
3397 The default value is the maximum amount of available memory to the JVM
3398 process or 128 GB, whichever is lower.
3399 .RS
3400 .PP
3401 The maximum amount of available memory to the JVM process is the minimum
3402 of the machine\[aq]s physical memory and any constraints set by the
3403 environment (e.g.
3404 container).
3405 .PP
3406 Specifying this option disables automatic use of compressed oops if the
3407 combined result of this and other options influencing the maximum amount
3408 of memory is larger than the range of memory addressable by compressed
3409 oops.
3410 See \f[CB]\-XX:UseCompressedOops\f[R] for further information about
3411 compressed oops.
3412 .PP
3413 The following example shows how to set the maximum amount of available
3414 memory for sizing the Java heap to 2 GB:
3415 .RS
3416 .PP
3417 \f[CB]\-XX:MaxRAM=2G\f[R]
3418 .RE
3419 .RE
3420 .TP
3421 .B \f[CB]\-XX:MaxRAMPercentage=\f[R]\f[I]percent\f[R]
3422 Sets the maximum amount of memory that the JVM may use for the Java heap
3423 before applying ergonomics heuristics as a percentage of the maximum
3424 amount determined as described in the \f[CB]\-XX:MaxRAM\f[R] option.
3425 The default value is 25 percent.
3426 .RS
3427 .PP
3428 Specifying this option disables automatic use of compressed oops if the
3429 combined result of this and other options influencing the maximum amount
3430 of memory is larger than the range of memory addressable by compressed
3431 oops.
3432 See \f[CB]\-XX:UseCompressedOops\f[R] for further information about
3433 compressed oops.
3434 .PP
3435 The following example shows how to set the percentage of the maximum
3436 amount of memory used for the Java heap:
3437 .RS
3438 .PP
3439 \f[CB]\-XX:MaxRAMPercentage=75\f[R]
3440 .RE
3441 .RE
3442 .TP
3443 .B \f[CB]\-XX:MinRAMPercentage=\f[R]\f[I]percent\f[R]
3444 Sets the maximum amount of memory that the JVM may use for the Java heap
3445 before applying ergonomics heuristics as a percentage of the maximum
3446 amount determined as described in the \f[CB]\-XX:MaxRAM\f[R] option for
3447 small heaps.
3448 A small heap is a heap of approximately 125 MB.
3449 The default value is 50 percent.
3450 .RS
3451 .PP
3452 The following example shows how to set the percentage of the maximum
3453 amount of memory used for the Java heap for small heaps:
3454 .RS
3455 .PP
3456 \f[CB]\-XX:MinRAMPercentage=75\f[R]
3457 .RE
3458 .RE
3459 .TP
3460 .B \f[CB]\-XX:MaxTenuringThreshold=\f[R]\f[I]threshold\f[R]
3461 Sets the maximum tenuring threshold for use in adaptive GC sizing.
3462 The largest value is 15.
3463 The default value is 15 for the parallel (throughput) collector, and 6
3464 for the CMS collector.
3465 .RS
3466 .PP
3467 The following example shows how to set the maximum tenuring threshold to
3468 10:
3469 .RS
3470 .PP
3471 \f[CB]\-XX:MaxTenuringThreshold=10\f[R]
3472 .RE
3473 .RE
3474 .TP
3475 .B \f[CB]\-XX:MetaspaceSize=\f[R]\f[I]size\f[R]
3476 Sets the size of the allocated class metadata space that triggers a
3477 garbage collection the first time it\[aq]s exceeded.
3478 This threshold for a garbage collection is increased or decreased
3479 depending on the amount of metadata used.
3480 The default size depends on the platform.
3481 .RS
3482 .RE
3483 .TP
3484 .B \f[CB]\-XX:MinHeapFreeRatio=\f[R]\f[I]percent\f[R]
3485 Sets the minimum allowed percentage of free heap space (0 to 100) after
3486 a GC event.
3487 If free heap space falls below this value, then the heap is expanded.
3488 By default, this value is set to 40%.
3489 .RS
3490 .PP
3491 Minimize Java heap size by lowering the values of the parameters
3492 \f[CB]MaxHeapFreeRatio\f[R] (default value is 70%) and
3493 \f[CB]MinHeapFreeRatio\f[R] (default value is 40%) with the command\-line
3494 options \f[CB]\-XX:MaxHeapFreeRatio\f[R] and
3495 \f[CB]\-XX:MinHeapFreeRatio\f[R].
3496 Lowering \f[CB]MaxHeapFreeRatio\f[R] to as low as 10% and
3497 \f[CB]MinHeapFreeRatio\f[R] to 5% has successfully reduced the heap size
3498 without too much performance regression; however, results may vary
3499 greatly depending on your application.
3500 Try different values for these parameters until they\[aq]re as low as
3501 possible, yet still retain acceptable performance.
3502 .RS
3503 .PP
3504 \f[CB]\-XX:MaxHeapFreeRatio=10\ \-XX:MinHeapFreeRatio=5\f[R]
3505 .RE
3506 .PP
3507 Customers trying to keep the heap small should also add the option
3508 \f[CB]\-XX:\-ShrinkHeapInSteps\f[R].
3509 See \f[B]Performance Tuning Examples\f[R] for a description of using this
3510 option to keep the Java heap small by reducing the dynamic footprint for
3511 embedded applications.
3512 .RE
3513 .TP
3514 .B \f[CB]\-XX:MinHeapSize=\f[R]\f[I]size\f[R]
3515 Sets the minimum size (in bytes) of the memory allocation pool.
3516 This value must be either 0, or a multiple of 1024 and greater than 1
3517 MB.
3518 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
3519 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
3520 \f[CB]G\f[R] to indicate gigabytes.
3521 The default value is selected at run time based on the system
3522 configuration.
3523 .RS
3524 .PP
3525 The following examples show how to set the mimimum size of allocated
3526 memory to 6 MB using various units:
3527 .IP
3528 .nf
3529 \f[CB]
3530 \-XX:MinHeapSize=6291456
3531 \-XX:MinHeapSize=6144k
3532 \-XX:MinHeapSize=6m
3533 \f[R]
3534 .fi
3535 .PP
3536 If you set this option to 0, then the minimum size is set to the same
3537 value as the initial size.
3538 .RE
3539 .TP
3540 .B \f[CB]\-XX:NewRatio=\f[R]\f[I]ratio\f[R]
3541 Sets the ratio between young and old generation sizes.
3542 By default, this option is set to 2.
3543 The following example shows how to set the young\-to\-old ratio to 1:
3544 .RS
3545 .RS
3546 .PP
3547 \f[CB]\-XX:NewRatio=1\f[R]
3548 .RE
3549 .RE
3550 .TP
3551 .B \f[CB]\-XX:NewSize=\f[R]\f[I]size\f[R]
3552 Sets the initial size (in bytes) of the heap for the young generation
3553 (nursery).
3554 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
3555 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
3556 \f[CB]G\f[R] to indicate gigabytes.
3557 .RS
3558 .PP
3559 The young generation region of the heap is used for new objects.
3560 GC is performed in this region more often than in other regions.
3561 If the size for the young generation is too low, then a large number of
3562 minor GCs are performed.
3563 If the size is too high, then only full GCs are performed, which can
3564 take a long time to complete.
3565 It is recommended that you keep the size for the young generation
3566 greater than 25% and less than 50% of the overall heap size.
3567 .PP
3568 The following examples show how to set the initial size of the young
3569 generation to 256 MB using various units:
3570 .IP
3571 .nf
3572 \f[CB]
3573 \-XX:NewSize=256m
3574 \-XX:NewSize=262144k
3575 \-XX:NewSize=268435456
3576 \f[R]
3577 .fi
3578 .PP
3579 The \f[CB]\-XX:NewSize\f[R] option is equivalent to \f[CB]\-Xmn\f[R].
3580 .RE
3581 .TP
3582 .B \f[CB]\-XX:ParallelGCThreads=\f[R]\f[I]threads\f[R]
3583 Sets the number of the stop\-the\-world (STW) worker threads.
3584 The default value depends on the number of CPUs available to the JVM and
3585 the garbage collector selected.
3586 .RS
3587 .PP
3588 For example, to set the number of threads for G1 GC to 2, specify the
3589 following option:
3590 .RS
3591 .PP
3592 \f[CB]\-XX:ParallelGCThreads=2\f[R]
3593 .RE
3594 .RE
3595 .TP
3596 .B \f[CB]\-XX:+ParallelRefProcEnabled\f[R]
3597 Enables parallel reference processing.
3598 By default, this option is disabled.
3599 .RS
3600 .RE
3601 .TP
3602 .B \f[CB]\-XX:+PrintAdaptiveSizePolicy\f[R]
3603 Enables printing of information about adaptive\-generation sizing.
3604 By default, this option is disabled.
3605 .RS
3606 .RE
3607 .TP
3608 .B \f[CB]\-XX:+ScavengeBeforeFullGC\f[R]
3609 Enables GC of the young generation before each full GC.
3610 This option is enabled by default.
3611 It is recommended that you \f[I]don\[aq]t\f[R] disable it, because
3612 scavenging the young generation before a full GC can reduce the number
3613 of objects reachable from the old generation space into the young
3614 generation space.
3615 To disable GC of the young generation before each full GC, specify the
3616 option \f[CB]\-XX:\-ScavengeBeforeFullGC\f[R].
3617 .RS
3618 .RE
3619 .TP
3620 .B \f[CB]\-XX:SoftRefLRUPolicyMSPerMB=\f[R]\f[I]time\f[R]
3621 Sets the amount of time (in milliseconds) a softly reachable object is
3622 kept active on the heap after the last time it was referenced.
3623 The default value is one second of lifetime per free megabyte in the
3624 heap.
3625 The \f[CB]\-XX:SoftRefLRUPolicyMSPerMB\f[R] option accepts integer values
3626 representing milliseconds per one megabyte of the current heap size (for
3627 Java HotSpot Client VM) or the maximum possible heap size (for Java
3628 HotSpot Server VM).
3629 This difference means that the Client VM tends to flush soft references
3630 rather than grow the heap, whereas the Server VM tends to grow the heap
3631 rather than flush soft references.
3632 In the latter case, the value of the \f[CB]\-Xmx\f[R] option has a
3633 significant effect on how quickly soft references are garbage collected.
3634 .RS
3635 .PP
3636 The following example shows how to set the value to 2.5 seconds:
3637 .PP
3638 \f[CB]\-XX:SoftRefLRUPolicyMSPerMB=2500\f[R]
3639 .RE
3640 .TP
3641 .B \f[CB]\-XX:\-ShrinkHeapInSteps\f[R]
3642 Incrementally reduces the Java heap to the target size, specified by the
3643 option \f[CB]\-XX:MaxHeapFreeRatio\f[R].
3644 This option is enabled by default.
3645 If disabled, then it immediately reduces the Java heap to the target
3646 size instead of requiring multiple garbage collection cycles.
3647 Disable this option if you want to minimize the Java heap size.
3648 You will likely encounter performance degradation when this option is
3649 disabled.
3650 .RS
3651 .PP
3652 See \f[B]Performance Tuning Examples\f[R] for a description of using the
3653 \f[CB]MaxHeapFreeRatio\f[R] option to keep the Java heap small by reducing
3654 the dynamic footprint for embedded applications.
3655 .RE
3656 .TP
3657 .B \f[CB]\-XX:StringDeduplicationAgeThreshold=\f[R]\f[I]threshold\f[R]
3658 Identifies \f[CB]String\f[R] objects reaching the specified age that are
3659 considered candidates for deduplication.
3660 An object\[aq]s age is a measure of how many times it has survived
3661 garbage collection.
3662 This is sometimes referred to as tenuring.
3663 .RS
3664 .RS
3665 .PP
3666 \f[B]Note:\f[R] \f[CB]String\f[R] objects that are promoted to an old heap
3667 region before this age has been reached are always considered candidates
3668 for deduplication.
3669 The default value for this option is \f[CB]3\f[R].
3670 See the \f[CB]\-XX:+UseStringDeduplication\f[R] option.
3671 .RE
3672 .RE
3673 .TP
3674 .B \f[CB]\-XX:SurvivorRatio=\f[R]\f[I]ratio\f[R]
3675 Sets the ratio between eden space size and survivor space size.
3676 By default, this option is set to 8.
3677 The following example shows how to set the eden/survivor space ratio to
3678 4:
3679 .RS
3680 .RS
3681 .PP
3682 \f[CB]\-XX:SurvivorRatio=4\f[R]
3683 .RE
3684 .RE
3685 .TP
3686 .B \f[CB]\-XX:TargetSurvivorRatio=\f[R]\f[I]percent\f[R]
3687 Sets the desired percentage of survivor space (0 to 100) used after
3688 young garbage collection.
3689 By default, this option is set to 50%.
3690 .RS
3691 .PP
3692 The following example shows how to set the target survivor space ratio
3693 to 30%:
3694 .RS
3695 .PP
3696 \f[CB]\-XX:TargetSurvivorRatio=30\f[R]
3697 .RE
3698 .RE
3699 .TP
3700 .B \f[CB]\-XX:TLABSize=\f[R]\f[I]size\f[R]
3701 Sets the initial size (in bytes) of a thread\-local allocation buffer
3702 (TLAB).
3703 Append the letter \f[CB]k\f[R] or \f[CB]K\f[R] to indicate kilobytes,
3704 \f[CB]m\f[R] or \f[CB]M\f[R] to indicate megabytes, or \f[CB]g\f[R] or
3705 \f[CB]G\f[R] to indicate gigabytes.
3706 If this option is set to 0, then the JVM selects the initial size
3707 automatically.
3708 .RS
3709 .PP
3710 The following example shows how to set the initial TLAB size to 512 KB:
3711 .RS
3712 .PP
3713 \f[CB]\-XX:TLABSize=512k\f[R]
3714 .RE
3715 .RE
3716 .TP
3717 .B \f[CB]\-XX:+UseAdaptiveSizePolicy\f[R]
3718 Enables the use of adaptive generation sizing.
3719 This option is enabled by default.
3720 To disable adaptive generation sizing, specify
3721 \f[CB]\-XX:\-UseAdaptiveSizePolicy\f[R] and set the size of the memory
3722 allocation pool explicitly.
3723 See the \f[CB]\-XX:SurvivorRatio\f[R] option.
3724 .RS
3725 .RE
3726 .TP
3727 .B \f[CB]\-XX:+UseCMSInitiatingOccupancyOnly\f[R]
3728 Enables the use of the occupancy value as the only criterion for
3729 initiating the CMS collector.
3730 By default, this option is disabled and other criteria may be used.
3731 .RS
3732 .RE
3733 .TP
3734 .B \f[CB]\-XX:+UseG1GC\f[R]
3735 Enables the use of the garbage\-first (G1) garbage collector.
3736 It\[aq]s a server\-style garbage collector, targeted for multiprocessor
3737 machines with a large amount of RAM.
3738 This option meets GC pause time goals with high probability, while
3739 maintaining good throughput.
3740 The G1 collector is recommended for applications requiring large heaps
3741 (sizes of around 6 GB or larger) with limited GC latency requirements (a
3742 stable and predictable pause time below 0.5 seconds).
3743 By default, this option is enabled and G1 is used as the default garbage
3744 collector.
3745 .RS
3746 .RE
3747 .TP
3748 .B \f[CB]\-XX:+UseGCOverheadLimit\f[R]
3749 Enables the use of a policy that limits the proportion of time spent by
3750 the JVM on GC before an \f[CB]OutOfMemoryError\f[R] exception is thrown.
3751 This option is enabled, by default, and the parallel GC will throw an
3752 \f[CB]OutOfMemoryError\f[R] if more than 98% of the total time is spent on
3753 garbage collection and less than 2% of the heap is recovered.
3754 When the heap is small, this feature can be used to prevent applications
3755 from running for long periods of time with little or no progress.
3756 To disable this option, specify the option
3757 \f[CB]\-XX:\-UseGCOverheadLimit\f[R].
3758 .RS
3759 .RE
3760 .TP
3761 .B \f[CB]\-XX:+UseNUMA\f[R]
3762 Enables performance optimization of an application on a machine with
3763 nonuniform memory architecture (NUMA) by increasing the
3764 application\[aq]s use of lower latency memory.
3765 By default, this option is disabled and no optimization for NUMA is
3766 made.
3767 The option is available only when the parallel garbage collector is used
3768 (\f[CB]\-XX:+UseParallelGC\f[R]).
3769 .RS
3770 .RE
3771 .TP
3772 .B \f[CB]\-XX:+UseParallelGC\f[R]
3773 Enables the use of the parallel scavenge garbage collector (also known
3774 as the throughput collector) to improve the performance of your
3775 application by leveraging multiple processors.
3776 .RS
3777 .PP
3778 By default, this option is disabled and the default collector is used.
3779 If it\[aq]s enabled, then the \f[CB]\-XX:+UseParallelOldGC\f[R] option is
3780 automatically enabled, unless you explicitly disable it.
3781 .RE
3782 .TP
3783 .B \f[CB]\-XX:+UseParallelOldGC\f[R]
3784 Enables the use of the parallel garbage collector for full GCs.
3785 By default, this option is disabled.
3786 Enabling it automatically enables the \f[CB]\-XX:+UseParallelGC\f[R]
3787 option.
3788 .RS
3789 .RE
3790 .TP
3791 .B \f[CB]\-XX:+UseSerialGC\f[R]
3792 Enables the use of the serial garbage collector.
3793 This is generally the best choice for small and simple applications that
3794 don\[aq]t require any special functionality from garbage collection.
3795 By default, this option is disabled and the default collector is used.
3796 .RS
3797 .RE
3798 .TP
3799 .B \f[CB]\-XX:+UseSHM\f[R]
3800 \f[B]Linux only:\f[R] Enables the JVM to use shared memory to set up
3801 large pages.
3802 .RS
3803 .PP
3804 See \f[B]Large Pages\f[R] for setting up large pages.
3805 .RE
3806 .TP
3807 .B \f[CB]\-XX:+UseStringDeduplication\f[R]
3808 Enables string deduplication.
3809 By default, this option is disabled.
3810 To use this option, you must enable the garbage\-first (G1) garbage
3811 collector.
3812 .RS
3813 .PP
3814 String deduplication reduces the memory footprint of \f[CB]String\f[R]
3815 objects on the Java heap by taking advantage of the fact that many
3816 \f[CB]String\f[R] objects are identical.
3817 Instead of each \f[CB]String\f[R] object pointing to its own character
3818 array, identical \f[CB]String\f[R] objects can point to and share the same
3819 character array.
3820 .RE
3821 .TP
3822 .B \f[CB]\-XX:+UseTLAB\f[R]
3823 Enables the use of thread\-local allocation blocks (TLABs) in the young
3824 generation space.
3825 This option is enabled by default.
3826 To disable the use of TLABs, specify the option \f[CB]\-XX:\-UseTLAB\f[R].
3827 .RS
3828 .RE
3829 .TP
3830 .B \f[CB]\-XX:+UseZGC\f[R]
3831 Enables the use of the Z garbage collector.
3832 This garbage collector is best for providing lowest latency with large
3833 Java heaps at some throughput cost.
3834 This is an experimental garbage collector, you need to specify
3835 \f[CB]\-XX:+UnlockExperimentalVMOptions\f[R] before \f[CB]\-XX:+UseZGC\f[R]
3836 on the command line.
3837 .RS
3838 .PP
3839 Example:
3840 .RS
3841 .PP
3842 \f[CB]\-XX:+UnlockExperimentalVMOptions\ \-XX:+UseZGC\f[R]
3843 .RE
3844 .RE
3845 .SH DEPRECATED JAVA OPTIONS
3846 .PP
3847 These \f[CB]java\f[R] options are deprecated and might be removed in a
3848 future JDK release.
3849 They\[aq]re still accepted and acted upon, but a warning is issued when
3850 they\[aq]re used.
3851 .TP
3852 .B \f[CB]\-Xfuture\f[R]
3853 Enables strict class\-file format checks that enforce close conformance
3854 to the class\-file format specification.
3855 Developers should use this flag when developing new code.
3856 Stricter checks may become the default in future releases.
3857 .RS
3858 .RE
3859 .TP
3860 .B \f[CB]\-Xloggc:\f[R]\f[I]filename\f[R]
3861 Sets the file to which verbose GC events information should be
3862 redirected for logging.
3863 The \f[CB]\-Xloggc\f[R] option overrides \f[CB]\-verbose:gc\f[R] if both are
3864 given with the same java command.
3865 \f[CB]\-Xloggc:\f[R]\f[I]filename\f[R] is replaced by
3866 \f[CB]\-Xlog:gc:\f[R]\f[I]filename\f[R].
3867 See Enable Logging with the JVM Unified Logging Framework.
3868 .RS
3869 .PP
3870 Example:
3871 .PP
3872 \f[CB]\-Xlog:gc:garbage\-collection.log\f[R]
3873 .RE
3874 .TP
3875 .B \f[CB]\-XX:+FailOverToOldVerifier\f[R]
3876 Enables automatic failover to the old verifier when the new type checker
3877 fails.
3878 By default, this option is disabled and it\[aq]s ignored (that is,
3879 treated as disabled) for classes with a recent bytecode version.
3880 You can enable it only for classes with older versions of the bytecode.
3881 .RS
3882 .RE
3883 .TP
3884 .B \f[CB]\-XX:+FlightRecorder\f[R]
3885 Enables the use of Java Flight Recorder (JFR) during the runtime of the
3886 application.
3887 Since JDK 8u40 this option has not been required to use JFR.
3888 .RS
3889 .RE
3890 .TP
3891 .B \f[CB]\-XX:InitialRAMFraction=\f[R]\f[I]ratio\f[R]
3892 Sets the initial amount of memory that the JVM may use for the Java heap
3893 before applying ergonomics heuristics as a ratio of the maximum amount
3894 determined as described in the \f[CB]\-XX:MaxRAM\f[R] option.
3895 The default value is 64.
3896 .RS
3897 .PP
3898 Use the option \f[CB]\-XX:InitialRAMPercentage\f[R] instead.
3899 .RE
3900 .TP
3901 .B \f[CB]\-XX:MaxRAMFraction=\f[R]\f[I]ratio\f[R]
3902 Sets the maximum amount of memory that the JVM may use for the Java heap
3903 before applying ergonomics heuristics as a fraction of the maximum
3904 amount determined as described in the \f[CB]\-XX:MaxRAM\f[R] option.
3905 The default value is 4.
3906 .RS
3907 .PP
3908 Specifying this option disables automatic use of compressed oops if the
3909 combined result of this and other options influencing the maximum amount
3910 of memory is larger than the range of memory addressable by compressed
3911 oops.
3912 See \f[CB]\-XX:UseCompressedOops\f[R] for further information about
3913 compressed oops.
3914 .PP
3915 Use the option \f[CB]\-XX:MaxRAMPercentage\f[R] instead.
3916 .RE
3917 .TP
3918 .B \f[CB]\-XX:MinRAMFraction=\f[R]\f[I]ratio\f[R]
3919 Sets the maximum amount of memory that the JVM may use for the Java heap
3920 before applying ergonomics heuristics as a fraction of the maximum
3921 amount determined as described in the \f[CB]\-XX:MaxRAM\f[R] option for
3922 small heaps.
3923 A small heap is a heap of approximately 125 MB.
3924 The default value is 2.
3925 .RS
3926 .PP
3927 Use the option \f[CB]\-XX:MinRAMPercentage\f[R] instead.
3928 .RE
3929 .TP
3930 .B \f[CB]\-XX:+TraceClassLoading\f[R]
3931 Enables tracing of classes as they are loaded.
3932 By default, this option is disabled and classes aren\[aq]t traced.
3933 .RS
3934 .PP
3935 The replacement Unified Logging syntax is
3936 \f[CB]\-Xlog:class+load=\f[R]\f[I]level\f[R].
3937 See \f[B]Enable Logging with the JVM Unified Logging Framework\f[R]
3938 .PP
3939 Use \f[I]level\f[R]=\f[CB]info\f[R] for regular information, or
3940 \f[I]level\f[R]=\f[CB]debug\f[R] for additional information.
3941 In Unified Logging syntax, \f[CB]\-verbose:class\f[R] equals
3942 \f[CB]\-Xlog:class+load=info,class+unload=info\f[R].
3943 .RE
3944 .TP
3945 .B \f[CB]\-XX:+TraceClassLoadingPreorder\f[R]
3946 Enables tracing of all loaded classes in the order in which they\[aq]re
3947 referenced.
3948 By default, this option is disabled and classes aren\[aq]t traced.
3949 .RS
3950 .PP
3951 The replacement Unified Logging syntax is
3952 \f[CB]\-Xlog:class+preorder=debug\f[R].
3953 See \f[B]Enable Logging with the JVM Unified Logging Framework\f[R].
3954 .RE
3955 .TP
3956 .B \f[CB]\-XX:+TraceClassResolution\f[R]
3957 Enables tracing of constant pool resolutions.
3958 By default, this option is disabled and constant pool resolutions
3959 aren\[aq]t traced.
3960 .RS
3961 .PP
3962 The replacement Unified Logging syntax is
3963 \f[CB]\-Xlog:class+resolve=debug\f[R].
3964 See \f[B]Enable Logging with the JVM Unified Logging Framework\f[R].
3965 .RE
3966 .TP
3967 .B \f[CB]\-XX:+TraceLoaderConstraints\f[R]
3968 Enables tracing of the loader constraints recording.
3969 By default, this option is disabled and loader constraints recording
3970 isn\[aq]t traced.
3971 .RS
3972 .PP
3973 The replacement Unified Logging syntax is
3974 \f[CB]\-Xlog:class+loader+constraints=info\f[R].
3975 See \f[B]Enable Logging with the JVM Unified Logging Framework\f[R].
3976 .RE
3977 .TP
3978 .B \f[CB]\-XX:+UseConcMarkSweepGC\f[R]
3979 Enables the use of the CMS garbage collector for the old generation.
3980 CMS is an alternative to the default garbage collector (G1), which also
3981 focuses on meeting application latency requirements.
3982 By default, this option is disabled and the collector is selected
3983 automatically based on the configuration of the machine and type of the
3984 JVM.
3985 The CMS garbage collector is deprecated.
3986 .RS
3987 .RE
3988 .SH OBSOLETE JAVA OPTIONS
3989 .PP
3990 These \f[CB]java\f[R] options are still accepted but ignored, and a
3991 warning is issued when they\[aq]re used.
3992 .TP
3993 .B \f[CB]\-XX:+UseMembar\f[R]
3994 Enabled issuing membars on thread\-state transitions.
3995 This option was disabled by default on all platforms except ARM servers,
3996 where it was enabled.
3997 .RS
3998 .RE
3999 .TP
4000 .B \f[CB]\-XX:MaxPermSize=\f[R]\f[I]size\f[R]
4001 Sets the maximum permanent generation space size (in bytes).
4002 This option was deprecated in JDK 8 and superseded by the
4003 \f[CB]\-XX:MaxMetaspaceSize\f[R] option.
4004 .RS
4005 .RE
4006 .TP
4007 .B \f[CB]\-XX:PermSize=\f[R]\f[I]size\f[R]
4008 Sets the space (in bytes) allocated to the permanent generation that
4009 triggers a garbage collection if it\[aq]s exceeded.
4010 This option was deprecated in JDK 8 and superseded by the
4011 \f[CB]\-XX:MetaspaceSize\f[R] option.
4012 .RS
4013 .RE
4014 .SH REMOVED JAVA OPTIONS
4015 .PP
4016 These \f[CB]java\f[R] options have been removed in JDK 13 and using them
4017 results in an error of:
4018 .RS
4019 .PP
4020 \f[CB]Unrecognized\ VM\ option\f[R] \f[I]option\-name\f[R]
4021 .RE
4022 .TP
4023 .B \f[CB]\-XX:+AggressiveOpts\f[R]
4024 Enabled the use of aggressive performance optimization features.
4025 By default, this option was disabled and experimental performance
4026 features were not used.
4027 .RS
4028 .RE
4029 .PP
4030 For the lists and descriptions of options removed in previous releases
4031 see the \f[I]Removed Java Options\f[R] section in:
4032 .IP \[bu] 2
4033 \f[B]Java Platform, Standard Edition Tools Reference, Release 12\f[R]
4034 [https://docs.oracle.com/en/java/javase/12/tools/java.html#GUID\-3B1CE181\-CD30\-4178\-9602\-230B800D4FAE]
4035 .IP \[bu] 2
4036 \f[B]Java Platform, Standard Edition Tools Reference, Release 11\f[R]
4037 [https://docs.oracle.com/en/java/javase/11/tools/java.html#GUID\-741FC470\-AA3E\-494A\-8D2B\-1B1FE4A990D1]
4038 .IP \[bu] 2
4039 \f[B]Java Platform, Standard Edition Tools Reference, Release 10\f[R]
4040 [https://docs.oracle.com/javase/10/tools/java.htm#JSWOR624]
4041 .IP \[bu] 2
4042 \f[B]Java Platform, Standard Edition Tools Reference, Release 9\f[R]
4043 [https://docs.oracle.com/javase/9/tools/java.htm#JSWOR624]
4044 .IP \[bu] 2
4045 \f[B]Java Platform, Standard Edition Tools Reference, Release 8 for
4046 Oracle JDK on Windows\f[R]
4047 [https://docs.oracle.com/javase/8/docs/technotes/tools/windows/java.html#BGBCIEFC]
4048 .IP \[bu] 2
4049 \f[B]Java Platform, Standard Edition Tools Reference, Release 8 for
4050 Oracle JDK on Solaris, Linux, and macOS\f[R]
4051 [https://docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html#BGBCIEFC]
4052 .SH JAVA COMMAND\-LINE ARGUMENT FILES
4053 .PP
4054 You can shorten or simplify the \f[CB]java\f[R] command by using
4055 \f[CB]\@\f[R] argument files to specify one or more text files that
4056 contain arguments, such as options and class names, which are passed to
4057 the \f[CB]java\f[R] command.
4058 This let\[aq]s you to create \f[CB]java\f[R] commands of any length on any
4059 operating system.
4060 .PP
4061 In the command line, use the at sign (\f[CB]\@\f[R]) prefix to identify an
4062 argument file that contains \f[CB]java\f[R] options and class names.
4063 When the \f[CB]java\f[R] command encounters a file beginning with the at
4064 sign (\f[CB]\@\f[R]), it expands the contents of that file into an
4065 argument list just as they would be specified on the command line.
4066 .PP
4067 The \f[CB]java\f[R] launcher expands the argument file contents until it
4068 encounters the \f[CB]\-\-disable\-\@files\f[R] option.
4069 You can use the \f[CB]\-\-disable\-\@files\f[R] option anywhere on the
4070 command line, including in an argument file, to stop \f[CB]\@\f[R]
4071 argument files expansion.
4072 .PP
4073 The following items describe the syntax of \f[CB]java\f[R] argument files:
4074 .IP \[bu] 2
4075 The argument file must contain only ASCII characters or characters in
4076 system default encoding that\[aq]s ASCII friendly, such as UTF\-8.
4077 .IP \[bu] 2
4078 The argument file size must not exceed MAXINT (2,147,483,647) bytes.
4079 .IP \[bu] 2
4080 The launcher doesn\[aq]t expand wildcards that are present within an
4081 argument file.
4082 .IP \[bu] 2
4083 Use white space or new line characters to separate arguments included in
4084 the file.
4085 .IP \[bu] 2
4086 White space includes a white space character, \f[CB]\\t\f[R],
4087 \f[CB]\\n\f[R], \f[CB]\\r\f[R], and \f[CB]\\f\f[R].
4088 .RS 2
4089 .PP
4090 For example, it is possible to have a path with a space, such as
4091 \f[CB]c:\\Program\ Files\f[R] that can be specified as either
4092 \f[CB]"c:\\\\Program\ Files"\f[R] or, to avoid an escape,
4093 \f[CB]c:\\Program"\ "Files\f[R].
4094 .RE
4095 .IP \[bu] 2
4096 Any option that contains spaces, such as a path component, must be
4097 within quotation marks using quotation (\[aq]"\[aq]) characters in its
4098 entirety.
4099 .IP \[bu] 2
4100 A string within quotation marks may contain the characters \f[CB]\\n\f[R],
4101 \f[CB]\\r\f[R], \f[CB]\\t\f[R], and \f[CB]\\f\f[R].
4102 They are converted to their respective ASCII codes.
4103 \
4104 .IP \[bu] 2
4105 If a file name contains embedded spaces, then put the whole file name in
4106 double quotation marks.
4107 .IP \[bu] 2
4108 File names in an argument file are relative to the current directory,
4109 not to the location of the argument file.
4110 .IP \[bu] 2
4111 Use the number sign \f[CB]#\f[R] in the argument file to identify
4112 comments.
4113 All characters following the \f[CB]#\f[R] are ignored until the end of
4114 line.
4115 .IP \[bu] 2
4116 Additional at sign \f[CB]\@\f[R] prefixes to \f[CB]\@\f[R] prefixed options
4117 act as an escape, (the first \f[CB]\@\f[R] is removed and the rest of the
4118 arguments are presented to the launcher literally).
4119 .IP \[bu] 2
4120 Lines may be continued using the continuation character (\f[CB]\\\f[R]) at
4121 the end\-of\-line.
4122 The two lines are concatenated with the leading white spaces trimmed.
4123 To prevent trimming the \ leading white spaces, a continuation character
4124 (\f[CB]\\\f[R]) may be placed at the first column.
4125 .IP \[bu] 2
4126 Because backslash (\\) is an escape character, a backslash
4127 character\ must be escaped with another backslash character.
4128 .IP \[bu] 2
4129 Partial quote is allowed and is closed by an end\-of\-file.
4130 .IP \[bu] 2
4131 An open quote stops at end\-of\-line unless \f[CB]\\\f[R] is the last
4132 character, which then joins the next line by removing all leading white
4133 space characters.
4134 .IP \[bu] 2
4135 Wildcards (*) aren\[aq]t allowed in these lists (such as specifying
4136 \f[CB]*.java\f[R]).
4137 .IP \[bu] 2
4138 Use of the at sign (\f[CB]\@\f[R]) to recursively interpret files
4139 isn\[aq]t supported.
4140 .SS Example of Open or Partial Quotes in an Argument File
4141 .PP
4142 In the argument file,
4143 .IP
4144 .nf
4145 \f[CB]
4146 \-cp\ "lib/
4147 cool/
4148 app/
4149 jars
4150 \f[R]
4151 .fi
4152 .PP
4153 this is interpreted as:
4154 .RS
4155 .PP
4156 \f[CB]\-cp\ lib/cool/app/jars\f[R]
4157 .RE
4158 .SS Example of a Backslash Character\ Escaped with Another Backslash
4159 Character in an Argument File
4160 .PP
4161 To output the following:
4162 .RS
4163 .PP
4164 \f[CB]\-cp\ c:\\Program\ Files\ (x86)\\Java\\jre\\lib\\ext;c:\\Program\ Files\\Java\\jre9\\lib\\ext\f[R]
4165 .RE
4166 .PP
4167 The backslash character must be specified in the argument file as:
4168 .RS
4169 .PP
4170 \f[CB]\-cp\ \ "c:\\\\Program\ Files\ (x86)\\\\Java\\\\jre\\\\lib\\\\ext;c:\\\\Program\ Files\\\\Java\\\\jre9\\\\lib\\\\ext"\f[R]
4171 .RE
4172 .SS Example of an EOL Escape Used to Force Concatenation of Lines in an
4173 Argument File
4174 .PP
4175 In the argument file,
4176 .IP
4177 .nf
4178 \f[CB]
4179 \-cp\ "/lib/cool\ app/jars:\\
4180 \ \ \ \ /lib/another\ app/jars"
4181 \f[R]
4182 .fi
4183 .PP
4184 This is interpreted as:
4185 .RS
4186 .PP
4187 \f[CB]\-cp\ /lib/cool\ app/jars:/lib/another\ app/jars\f[R]
4188 .RE
4189 .SS Example of Line Continuation with Leading Spaces in an Argument File
4190 .PP
4191 In the argument file,
4192 .IP
4193 .nf
4194 \f[CB]
4195 \-cp\ "/lib/cool\\
4196 \\app/jars”
4197 \f[R]
4198 .fi
4199 .PP
4200 This is interpreted as:
4201 .PP
4202 \f[CB]\-cp\ /lib/cool\ app/jars\f[R]
4203 .SS Examples of Using Single Argument File
4204 .PP
4205 You can use a single argument file, such as \f[CB]myargumentfile\f[R] in
4206 the following example, to hold all required \f[CB]java\f[R] arguments:
4207 .RS
4208 .PP
4209 \f[CB]java\ \@myargumentfile\f[R]
4210 .RE
4211 .SS Examples of Using Argument Files with Paths
4212 .PP
4213 You can include relative paths in argument files; however, they\[aq]re
4214 relative to the current working directory and not to the paths of the
4215 argument files themselves.
4216 In the following example, \f[CB]path1/options\f[R] and
4217 \f[CB]path2/options\f[R] represent argument files with different paths.
4218 Any relative paths that they contain are relative to the current working
4219 directory and not to the argument files:
4220 .RS
4221 .PP
4222 \f[CB]java\ \@path1/options\ \@path2/classes\f[R]
4223 .RE
4224 .SH CODE HEAP STATE ANALYTICS
4225 .SS Overview
4226 .PP
4227 There are occasions when having insight into the current state of the
4228 JVM code heap would be helpful to answer questions such as:
4229 .IP \[bu] 2
4230 Why was the JIT turned off and then on again and again?
4231 .IP \[bu] 2
4232 Where has all the code heap space gone?
4233 .IP \[bu] 2
4234 Why is the method sweeper not working effectively?
4235 .PP
4236 To provide this insight, a code heap state analytics feature has been
4237 implemented that enables on\-the\-fly analysis of the code heap.
4238 The analytics process is divided into two parts.
4239 The first part examines the entire code heap and aggregates all
4240 information that is believed to be useful or important.
4241 The second part consists of several independent steps that print the
4242 collected information with an emphasis on different aspects of the data.
4243 Data collection and printing are done on an "on request" basis.
4244 .SS Syntax
4245 .PP
4246 Requests for real\-time, on\-the\-fly analysis can be issued with the
4247 following command:
4248 .RS
4249 .PP
4250 \f[CB]jcmd\f[R] \f[I]pid\f[R] \f[CB]Compiler.CodeHeap_Analytics\f[R]
4251 [\f[I]function\f[R]] [\f[I]granularity\f[R]]
4252 .RE
4253 .PP
4254 If you are only interested in how the code heap looks like after running
4255 a sample workload, you can use the command line option:
4256 .RS
4257 .PP
4258 \f[CB]\-Xlog:codecache=Trace\f[R]
4259 .RE
4260 .PP
4261 To see the code heap state when a "CodeCache full" condition exists,
4262 start the VM with the command line option:
4263 .RS
4264 .PP
4265 \f[CB]\-Xlog:codecache=Debug\f[R]
4266 .RE
4267 .PP
4268 See \f[B]CodeHeap State Analytics (OpenJDK)\f[R]
4269 [https://bugs.openjdk.java.net/secure/attachment/75649/JVM_CodeHeap_StateAnalytics_V2.pdf]
4270 for a detailed description of the code heap state analytics feature, the
4271 supported functions, and the granularity options.
4272 .SH ENABLE LOGGING WITH THE JVM UNIFIED LOGGING FRAMEWORK
4273 .PP
4274 You use the \f[CB]\-Xlog\f[R] option to configure or enable logging with
4275 the Java Virtual Machine (JVM) unified logging framework.
4276 .SS Synopsis
4277 .RS
4278 .PP
4279 \f[CB]\-Xlog\f[R][\f[CB]:\f[R][\f[I]what\f[R]][\f[CB]:\f[R][\f[I]output\f[R]][\f[CB]:\f[R][\f[I]decorators\f[R]][\f[CB]:\f[R]\f[I]output\-options\f[R][\f[CB],\f[R]...]]]]]
4280 .RE
4281 .TP
4282 .B \f[I]what\f[R]
4283 Specifies a combination of tags and levels of the form
4284 \f[I]tag1\f[R][\f[CB]+\f[R]\f[I]tag2\f[R]...][\f[CB]*\f[R]][\f[CB]=\f[R]\f[I]level\f[R]][\f[CB],\f[R]...].
4285 Unless the wildcard (\f[CB]*\f[R]) is specified, only log messages tagged
4286 with exactly the tags specified are matched.
4287 See \f[B]\-Xlog Tags and Levels\f[R].
4288 .RS
4289 .RE
4290 .TP
4291 .B \f[I]output\f[R]
4292 Sets the type of output.
4293 Omitting the \f[I]output\f[R] type defaults to \f[CB]stdout\f[R].
4294 See \f[B]\-Xlog Output\f[R].
4295 .RS
4296 .RE
4297 .TP
4298 .B \f[I]decorators\f[R]
4299 Configures the output to use a custom set of decorators.
4300 Omitting \f[I]decorators\f[R] defaults to \f[CB]uptime\f[R],
4301 \f[CB]level\f[R], and \f[CB]tags\f[R].
4302 See \f[B]Decorations\f[R].
4303 .RS
4304 .RE
4305 .TP
4306 .B \f[I]output\-options\f[R]
4307 Sets the \f[CB]\-Xlog\f[R] logging output options.
4308 .RS
4309 .RE
4310 .SS Description
4311 .PP
4312 The Java Virtual Machine (JVM) unified logging framework provides a
4313 common logging system for all components of the JVM.
4314 GC logging for the JVM has been changed to use the new logging
4315 framework.
4316 The mapping of old GC flags to the corresponding new Xlog configuration
4317 is described in \f[B]Convert GC Logging Flags to Xlog\f[R].
4318 In addition, runtime logging has also been changed to use the JVM
4319 unified logging framework.
4320 The mapping of legacy runtime logging flags to the corresponding new
4321 Xlog configuration is described in \f[B]Convert Runtime Logging Flags to
4322 Xlog\f[R].
4323 .PP
4324 The following provides quick reference to the \f[CB]\-Xlog\f[R] command
4325 and syntax for options:
4326 .TP
4327 .B \f[CB]\-Xlog\f[R]
4328 Enables JVM logging on an \f[CB]info\f[R] level.
4329 .RS
4330 .RE
4331 .TP
4332 .B \f[CB]\-Xlog:help\f[R]
4333 Prints \f[CB]\-Xlog\f[R] usage syntax and available tags, levels, and
4334 decorators along with example command lines with explanations.
4335 .RS
4336 .RE
4337 .TP
4338 .B \f[CB]\-Xlog:disable\f[R]
4339 Turns off all logging and clears all configuration of the logging
4340 framework including the default configuration for warnings and errors.
4341 .RS
4342 .RE
4343 .TP
4344 .B \f[CB]\-Xlog\f[R][\f[CB]:\f[R]\f[I]option\f[R]]
4345 Applies multiple arguments in the order that they appear on the command
4346 line.
4347 Multiple \f[CB]\-Xlog\f[R] arguments for the same output override each
4348 other in their given order.
4349 .RS
4350 .PP
4351 The \f[I]option\f[R] is set as:
4352 .RS
4353 .PP
4354 [\f[I]tag\-selection\f[R]][\f[CB]:\f[R][\f[I]output\f[R]][\f[CB]:\f[R][\f[I]decorators\f[R]][\f[CB]:\f[R]\f[I]output\-options\f[R]]]]
4355 .RE
4356 .PP
4357 Omitting the \f[I]tag\-selection\f[R] defaults to a tag\-set of
4358 \f[CB]all\f[R] and a level of \f[CB]info\f[R].
4359 .RS
4360 .PP
4361 \f[I]tag\f[R][\f[CB]+\f[R]...] \f[CB]all\f[R]
4362 .RE
4363 .PP
4364 The \f[CB]all\f[R] tag is a meta tag consisting of all tag\-sets
4365 available.
4366 The asterisk \f[CB]*\f[R] in a tag set definition denotes a wildcard tag
4367 match.
4368 Matching with a wildcard selects all tag sets that contain \f[I]at
4369 least\f[R] the specified tags.
4370 Without the wildcard, only exact matches of the specified tag sets are
4371 selected.
4372 .PP
4373 \f[I]output\-options\f[R] is
4374 .RS
4375 .PP
4376 \f[CB]filecount=\f[R]\f[I]file\-count\f[R] \f[CB]filesize=\f[R]\f[I]file size
4377 with optional K, M or G suffix\f[R]
4378 .RE
4379 .RE
4380 .SS Default Configuration
4381 .PP
4382 When the \f[CB]\-Xlog\f[R] option and nothing else is specified on the
4383 command line, the default configuration is used.
4384 The default configuration logs all messages with a level that matches
4385 either warning or error regardless of what tags the message is
4386 associated with.
4387 The default configuration is equivalent to entering the following on the
4388 command line:
4389 .RS
4390 .PP
4391 \f[CB]\-Xlog:all=warning:stdout:uptime,level,tags\f[R]
4392 .RE
4393 .SS Controlling Logging at Runtime
4394 .PP
4395 Logging can also be controlled at run time through Diagnostic Commands
4396 (with the \f[B]jcmd\f[R] utility).
4397 Everything that can be specified on the command line can also be
4398 specified dynamically with the \f[CB]VM.log\f[R] command.
4399 As the diagnostic commands are automatically exposed as MBeans, you can
4400 use JMX to change logging configuration at run time.
4401 .SS \-Xlog Tags and Levels
4402 .PP
4403 Each log message has a level and a tag set associated with it.
4404 The level of the message corresponds to its details, and the tag set
4405 corresponds to what the message contains or which JVM component it
4406 involves (such as, \f[CB]gc\f[R], \f[CB]jit\f[R], or \f[CB]os\f[R]).
4407 Mapping GC flags to the Xlog configuration is described in \f[B]Convert
4408 GC Logging Flags to Xlog\f[R].
4409 Mapping legacy runtime logging flags to the corresponding Xlog
4410 configuration is described in \f[B]Convert Runtime Logging Flags to
4411 Xlog\f[R].
4412 .PP
4413 \f[B]Available log levels:\f[R]
4414 .IP \[bu] 2
4415 \f[CB]off\f[R]
4416 .IP \[bu] 2
4417 \f[CB]trace\f[R]
4418 .IP \[bu] 2
4419 \f[CB]debug\f[R]
4420 .IP \[bu] 2
4421 \f[CB]info\f[R]
4422 .IP \[bu] 2
4423 \f[CB]warning\f[R]
4424 .IP \[bu] 2
4425 \f[CB]error\f[R]
4426 .PP
4427 \f[B]Available log tags:\f[R]
4428 .PP
4429 There are literally dozens of log tags, which in the right combinations,
4430 will enable a range of logging output.
4431 The full set of available log tags can be seen using
4432 \f[CB]\-Xlog:help\f[R].
4433 Specifying \f[CB]all\f[R] instead of a tag combination matches all tag
4434 combinations.
4435 .SS \-Xlog Output
4436 .PP
4437 The \f[CB]\-Xlog\f[R] option supports the following types of outputs:
4438 .IP \[bu] 2
4439 \f[CB]stdout\f[R] \-\-\- Sends output to stdout
4440 .IP \[bu] 2
4441 \f[CB]stderr\f[R] \-\-\- Sends output to stderr
4442 .IP \[bu] 2
4443 \f[CB]file=\f[R]\f[I]filename\f[R] \-\-\- Sends output to text file(s).
4444 .PP
4445 When using \f[CB]file=\f[R]\f[I]filename\f[R], specifying \f[CB]%p\f[R]
4446 and/or \f[CB]%t\f[R] in the file name expands to the JVM\[aq]s PID and
4447 startup timestamp, respectively.
4448 You can also configure text files to handle file rotation based on file
4449 size and a number of files to rotate.
4450 For example, to rotate the log file every 10 MB and keep 5 files in
4451 rotation, specify the options \f[CB]filesize=10M,\ filecount=5\f[R].
4452 The target size of the files isn\[aq]t guaranteed to be exact, it\[aq]s
4453 just an approximate value.
4454 Files are rotated by default with up to 5 rotated files of target size
4455 20 MB, unless configured otherwise.
4456 Specifying \f[CB]filecount=0\f[R] means that the log file shouldn\[aq]t be
4457 rotated.
4458 There\[aq]s a possibility of the pre\-existing log file getting
4459 overwritten.
4460 .SS Decorations
4461 .PP
4462 Logging messages are decorated with information about the message.
4463 You can configure each output to use a custom set of decorators.
4464 The order of the output is always the same as listed in the table.
4465 You can configure the decorations to be used at run time.
4466 Decorations are prepended to the log message.
4467 For example:
4468 .IP
4469 .nf
4470 \f[CB]
4471 [6.567s][info][gc,old]\ Old\ collection\ complete
4472 \f[R]
4473 .fi
4474 .PP
4475 Omitting \f[CB]decorators\f[R] defaults to \f[CB]uptime\f[R],
4476 \f[CB]level\f[R], and \f[CB]tags\f[R].
4477 The \f[CB]none\f[R] decorator is special and is used to turn off all
4478 decorations.
4479 .PP
4480 \f[CB]time\f[R] (\f[CB]t\f[R]), \f[CB]utctime\f[R] (\f[CB]utc\f[R]),
4481 \f[CB]uptime\f[R] (\f[CB]u\f[R]), \f[CB]timemillis\f[R] (\f[CB]tm\f[R]),
4482 \f[CB]uptimemillis\f[R] (\f[CB]um\f[R]), \f[CB]timenanos\f[R] (\f[CB]tn\f[R]),
4483 \f[CB]uptimenanos\f[R] (\f[CB]un\f[R]), \f[CB]hostname\f[R] (\f[CB]hn\f[R]),
4484 \f[CB]pid\f[R] (\f[CB]p\f[R]), \f[CB]tid\f[R] (\f[CB]ti\f[R]), \f[CB]level\f[R]
4485 (\f[CB]l\f[R]), \f[CB]tags\f[R] (\f[CB]tg\f[R]) decorators can also be
4486 specified as \f[CB]none\f[R] for no decoration.
4487 .PP
4488 .TS
4489 tab(@);
4490 lw(14.9n) lw(55.1n).
4491 T{
4492 Decorations
4493 T}@T{
4494 Description
4495 T}
4496 _
4497 T{
4498 \f[CB]time\f[R] or \f[CB]t\f[R]
4499 T}@T{
4500 Current time and date in ISO\-8601 format.
4501 T}
4502 T{
4503 \f[CB]utctime\f[R] or \f[CB]utc\f[R]
4504 T}@T{
4505 Universal Time Coordinated or Coordinated Universal Time.
4506 T}
4507 T{
4508 \f[CB]uptime\f[R] or \f[CB]u\f[R]
4509 T}@T{
4510 Time since the start of the JVM in seconds and milliseconds.
4511 For example, 6.567s.
4512 T}
4513 T{
4514 \f[CB]timemillis\f[R] or \f[CB]tm\f[R]
4515 T}@T{
4516 The same value as generated by \f[CB]System.currentTimeMillis()\f[R]
4517 T}
4518 T{
4519 \f[CB]uptimemillis\f[R] or \f[CB]um\f[R]
4520 T}@T{
4521 Milliseconds since the JVM started.
4522 T}
4523 T{
4524 \f[CB]timenanos\f[R] or \f[CB]tn\f[R]
4525 T}@T{
4526 The same value generated by \f[CB]System.nanoTime()\f[R].
4527 T}
4528 T{
4529 \f[CB]uptimenanos\f[R] or \f[CB]un\f[R]
4530 T}@T{
4531 Nanoseconds since the JVM started.
4532 T}
4533 T{
4534 \f[CB]hostname\f[R] or \f[CB]hn\f[R]
4535 T}@T{
4536 The host name.
4537 T}
4538 T{
4539 \f[CB]pid\f[R] or \f[CB]p\f[R]
4540 T}@T{
4541 The process identifier.
4542 T}
4543 T{
4544 \f[CB]tid\f[R] or \f[CB]ti\f[R]
4545 T}@T{
4546 The thread identifier.
4547 T}
4548 T{
4549 \f[CB]level\f[R] or \f[CB]l\f[R]
4550 T}@T{
4551 The level associated with the log message.
4552 T}
4553 T{
4554 \f[CB]tags\f[R] or \f[CB]tg\f[R]
4555 T}@T{
4556 The tag\-set associated with the log message.
4557 T}
4558 .TE
4559 .SS Convert GC Logging Flags to Xlog
4560 .PP
4561 .TS
4562 tab(@);
4563 lw(22.4n) lw(16.5n) lw(31.2n).
4564 T{
4565 Legacy Garbage Collection (GC) Flag
4566 T}@T{
4567 Xlog Configuration
4568 T}@T{
4569 Comment
4570 T}
4571 _
4572 T{
4573 \f[CB]G1PrintHeapRegions\f[R]
4574 T}@T{
4575 \f[CB]\-Xlog:gc+region=trace\f[R]
4576 T}@T{
4577 Not Applicable
4578 T}
4579 T{
4580 \f[CB]GCLogFileSize\f[R]
4581 T}@T{
4582 No configuration available
4583 T}@T{
4584 Log rotation is handled by the framework.
4585 T}
4586 T{
4587 \f[CB]NumberOfGCLogFiles\f[R]
4588 T}@T{
4589 Not Applicable
4590 T}@T{
4591 Log rotation is handled by the framework.
4592 T}
4593 T{
4594 \f[CB]PrintAdaptiveSizePolicy\f[R]
4595 T}@T{
4596 \f[CB]\-Xlog:gc+ergo*=\f[R]\f[I]level\f[R]
4597 T}@T{
4598 Use a \f[I]level\f[R] of \f[CB]debug\f[R] for most of the information, or a
4599 \f[I]level\f[R] of \f[CB]trace\f[R] for all of what was logged for
4600 \f[CB]PrintAdaptiveSizePolicy\f[R].
4601 T}
4602 T{
4603 \f[CB]PrintGC\f[R]
4604 T}@T{
4605 \f[CB]\-Xlog:gc\f[R]
4606 T}@T{
4607 Not Applicable
4608 T}
4609 T{
4610 \f[CB]PrintGCApplicationConcurrentTime\f[R]
4611 T}@T{
4612 \f[CB]\-Xlog:safepoint\f[R]
4613 T}@T{
4614 Note that \f[CB]PrintGCApplicationConcurrentTime\f[R] and
4615 \f[CB]PrintGCApplicationStoppedTime\f[R] are logged on the same tag and
4616 aren\[aq]t separated in the new logging.
4617 T}
4618 T{
4619 \f[CB]PrintGCApplicationStoppedTime\f[R]
4620 T}@T{
4621 \f[CB]\-Xlog:safepoint\f[R]
4622 T}@T{
4623 Note that \f[CB]PrintGCApplicationConcurrentTime\f[R] and
4624 \f[CB]PrintGCApplicationStoppedTime\f[R] are logged on the same tag and
4625 not separated in the new logging.
4626 T}
4627 T{
4628 \f[CB]PrintGCCause\f[R]
4629 T}@T{
4630 Not Applicable
4631 T}@T{
4632 GC cause is now always logged.
4633 T}
4634 T{
4635 \f[CB]PrintGCDateStamps\f[R]
4636 T}@T{
4637 Not Applicable
4638 T}@T{
4639 Date stamps are logged by the framework.
4640 T}
4641 T{
4642 \f[CB]PrintGCDetails\f[R]
4643 T}@T{
4644 \f[CB]\-Xlog:gc*\f[R]
4645 T}@T{
4646 Not Applicable
4647 T}
4648 T{
4649 \f[CB]PrintGCID\f[R]
4650 T}@T{
4651 Not Applicable
4652 T}@T{
4653 GC ID is now always logged.
4654 T}
4655 T{
4656 \f[CB]PrintGCTaskTimeStamps\f[R]
4657 T}@T{
4658 \f[CB]\-Xlog:gc+task*=debug\f[R]
4659 T}@T{
4660 Not Applicable
4661 T}
4662 T{
4663 \f[CB]PrintGCTimeStamps\f[R]
4664 T}@T{
4665 Not Applicable
4666 T}@T{
4667 Time stamps are logged by the framework.
4668 T}
4669 T{
4670 \f[CB]PrintHeapAtGC\f[R]
4671 T}@T{
4672 \f[CB]\-Xlog:gc+heap=trace\f[R]
4673 T}@T{
4674 Not Applicable
4675 T}
4676 T{
4677 \f[CB]PrintReferenceGC\f[R]
4678 T}@T{
4679 \f[CB]\-Xlog:gc+ref*=debug\f[R]
4680 T}@T{
4681 Note that in the old logging, \f[CB]PrintReferenceGC\f[R] had an effect
4682 only if \f[CB]PrintGCDetails\f[R] was also enabled.
4683 T}
4684 T{
4685 \f[CB]PrintStringDeduplicationStatistics\f[R]
4686 T}@T{
4687 `\-Xlog:gc+stringdedup*=debug
4688 T}@T{
4689 ` Not Applicable
4690 T}
4691 T{
4692 \f[CB]PrintTenuringDistribution\f[R]
4693 T}@T{
4694 \f[CB]\-Xlog:gc+age*=\f[R]\f[I]level\f[R]
4695 T}@T{
4696 Use a \f[I]level\f[R] of \f[CB]debug\f[R] for the most relevant
4697 information, or a \f[I]level\f[R] of \f[CB]trace\f[R] for all of what was
4698 logged for \f[CB]PrintTenuringDistribution\f[R].
4699 T}
4700 T{
4701 \f[CB]UseGCLogFileRotation\f[R]
4702 T}@T{
4703 Not Applicable
4704 T}@T{
4705 What was logged for \f[CB]PrintTenuringDistribution\f[R].
4706 T}
4707 .TE
4708 .SS Convert Runtime Logging Flags to Xlog
4709 .PP
4710 .TS
4711 tab(@);
4712 lw(15.0n) lw(20.2n) lw(34.7n).
4713 T{
4714 Legacy Runtime Flag
4715 T}@T{
4716 Xlog Configuration
4717 T}@T{
4718 Comment
4719 T}
4720 _
4721 T{
4722 \f[CB]TraceExceptions\f[R]
4723 T}@T{
4724 \f[CB]\-Xlog:exceptions=info\f[R]
4725 T}@T{
4726 Not Applicable
4727 T}
4728 T{
4729 \f[CB]TraceClassLoading\f[R]
4730 T}@T{
4731 \f[CB]\-Xlog:class+load=\f[R]\f[I]level\f[R]
4732 T}@T{
4733 Use \f[I]level\f[R]=\f[CB]info\f[R] for regular information, or
4734 \f[I]level\f[R]=\f[CB]debug\f[R] for additional information.
4735 In Unified Logging syntax, \f[CB]\-verbose:class\f[R] equals
4736 \f[CB]\-Xlog:class+load=info,class+unload=info\f[R].
4737 T}
4738 T{
4739 \f[CB]TraceClassLoadingPreorder\f[R]
4740 T}@T{
4741 \f[CB]\-Xlog:class+preorder=debug\f[R]
4742 T}@T{
4743 Not Applicable
4744 T}
4745 T{
4746 \f[CB]TraceClassUnloading\f[R]
4747 T}@T{
4748 \f[CB]\-Xlog:class+unload=\f[R]\f[I]level\f[R]
4749 T}@T{
4750 Use \f[I]level\f[R]=\f[CB]info\f[R] for regular information, or
4751 \f[I]level\f[R]=\f[CB]trace\f[R] for additional information.
4752 In Unified Logging syntax, \f[CB]\-verbose:class\f[R] equals
4753 \f[CB]\-Xlog:class+load=info,class+unload=info\f[R].
4754 T}
4755 T{
4756 \f[CB]VerboseVerification\f[R]
4757 T}@T{
4758 \f[CB]\-Xlog:verification=info\f[R]
4759 T}@T{
4760 Not Applicable
4761 T}
4762 T{
4763 \f[CB]TraceClassPaths\f[R]
4764 T}@T{
4765 \f[CB]\-Xlog:class+path=info\f[R]
4766 T}@T{
4767 Not Applicable
4768 T}
4769 T{
4770 \f[CB]TraceClassResolution\f[R]
4771 T}@T{
4772 \f[CB]\-Xlog:class+resolve=debug\f[R]
4773 T}@T{
4774 Not Applicable
4775 T}
4776 T{
4777 \f[CB]TraceClassInitialization\f[R]
4778 T}@T{
4779 \f[CB]\-Xlog:class+init=info\f[R]
4780 T}@T{
4781 Not Applicable
4782 T}
4783 T{
4784 \f[CB]TraceLoaderConstraints\f[R]
4785 T}@T{
4786 \f[CB]\-Xlog:class+loader+constraints=info\f[R]
4787 T}@T{
4788 Not Applicable
4789 T}
4790 T{
4791 \f[CB]TraceClassLoaderData\f[R]
4792 T}@T{
4793 \f[CB]\-Xlog:class+loader+data=\f[R]\f[I]level\f[R]
4794 T}@T{
4795 Use \f[I]level\f[R]=\f[CB]debug\f[R] for regular information or
4796 \f[I]level\f[R]=\f[CB]trace\f[R] for additional information.
4797 T}
4798 T{
4799 \f[CB]TraceSafepointCleanupTime\f[R]
4800 T}@T{
4801 \f[CB]\-Xlog:safepoint+cleanup=info\f[R]
4802 T}@T{
4803 Not Applicable
4804 T}
4805 T{
4806 \f[CB]TraceSafepoint\f[R]
4807 T}@T{
4808 \f[CB]\-Xlog:safepoint=debug\f[R]
4809 T}@T{
4810 Not Applicable
4811 T}
4812 T{
4813 \f[CB]TraceMonitorInflation\f[R]
4814 T}@T{
4815 \f[CB]\-Xlog:monitorinflation=debug\f[R]
4816 T}@T{
4817 Not Applicable
4818 T}
4819 T{
4820 \f[CB]TraceBiasedLocking\f[R]
4821 T}@T{
4822 \f[CB]\-Xlog:biasedlocking=\f[R]\f[I]level\f[R]
4823 T}@T{
4824 Use \f[I]level\f[R]=\f[CB]info\f[R] for regular information, or
4825 \f[I]level\f[R]=\f[CB]trace\f[R] for additional information.
4826 T}
4827 T{
4828 \f[CB]TraceRedefineClasses\f[R]
4829 T}@T{
4830 \f[CB]\-Xlog:redefine+class*=\f[R]\f[I]level\f[R]
4831 T}@T{
4832 \f[I]level\f[R]=\f[CB]info\f[R], \f[CB]debug\f[R], and \f[CB]trace\f[R] provide
4833 increasing amounts of information.
4834 T}
4835 .TE
4836 .SS \-Xlog Usage Examples
4837 .PP
4838 The following are \f[CB]\-Xlog\f[R] examples.
4839 .TP
4840 .B \f[CB]\-Xlog\f[R]
4841 Logs all messages by using the \f[CB]info\f[R] level to \f[CB]stdout\f[R]
4842 with \f[CB]uptime\f[R], \f[CB]levels\f[R], and \f[CB]tags\f[R] decorations.
4843 This is equivalent to using:
4844 .RS
4845 .RS
4846 .PP
4847 \f[CB]\-Xlog:all=info:stdout:uptime,levels,tags\f[R]
4848 .RE
4849 .RE
4850 .TP
4851 .B \f[CB]\-Xlog:gc\f[R]
4852 Logs messages tagged with the \f[CB]gc\f[R] tag using \f[CB]info\f[R] level
4853 to \f[CB]stdout\f[R].
4854 The default configuration for all other messages at level
4855 \f[CB]warning\f[R] is in effect.
4856 .RS
4857 .RE
4858 .TP
4859 .B \f[CB]\-Xlog:gc,safepoint\f[R]
4860 Logs messages tagged either with the \f[CB]gc\f[R] or \f[CB]safepoint\f[R]
4861 tags, both using the \f[CB]info\f[R] level, to \f[CB]stdout\f[R], with
4862 default decorations.
4863 Messages tagged with both \f[CB]gc\f[R] and \f[CB]safepoint\f[R] won\[aq]t
4864 be logged.
4865 .RS
4866 .RE
4867 .TP
4868 .B \f[CB]\-Xlog:gc+ref=debug\f[R]
4869 Logs messages tagged with both \f[CB]gc\f[R] and \f[CB]ref\f[R] tags, using
4870 the \f[CB]debug\f[R] level to \f[CB]stdout\f[R], with default decorations.
4871 Messages tagged only with one of the two tags won\[aq]t be logged.
4872 .RS
4873 .RE
4874 .TP
4875 .B \f[CB]\-Xlog:gc=debug:file=gc.txt:none\f[R]
4876 Logs messages tagged with the \f[CB]gc\f[R] tag using the \f[CB]debug\f[R]
4877 level to a file called \f[CB]gc.txt\f[R] with no decorations.
4878 The default configuration for all other messages at level
4879 \f[CB]warning\f[R] is still in effect.
4880 .RS
4881 .RE
4882 .TP
4883 .B \f[CB]\-Xlog:gc=trace:file=gctrace.txt:uptimemillis,pids:filecount=5,filesize=1024\f[R]
4884 Logs messages tagged with the \f[CB]gc\f[R] tag using the \f[CB]trace\f[R]
4885 level to a rotating file set with 5 files with size 1 MB with the base
4886 name \f[CB]gctrace.txt\f[R] and uses decorations \f[CB]uptimemillis\f[R] and
4887 \f[CB]pid\f[R].
4888 .RS
4889 .PP
4890 The default configuration for all other messages at level
4891 \f[CB]warning\f[R] is still in effect.
4892 .RE
4893 .TP
4894 .B \f[CB]\-Xlog:gc::uptime,tid\f[R]
4895 Logs messages tagged with the \f[CB]gc\f[R] tag using the default
4896 \[aq]info\[aq] level to default the output \f[CB]stdout\f[R] and uses
4897 decorations \f[CB]uptime\f[R] and \f[CB]tid\f[R].
4898 The default configuration for all other messages at level
4899 \f[CB]warning\f[R] is still in effect.
4900 .RS
4901 .RE
4902 .TP
4903 .B \f[CB]\-Xlog:gc*=info,safepoint*=off\f[R]
4904 Logs messages tagged with at least \f[CB]gc\f[R] using the \f[CB]info\f[R]
4905 level, but turns off logging of messages tagged with \f[CB]safepoint\f[R].
4906 Messages tagged with both \f[CB]gc\f[R] and \f[CB]safepoint\f[R] won\[aq]t
4907 be logged.
4908 .RS
4909 .RE
4910 .TP
4911 .B \f[CB]\-Xlog:disable\ \-Xlog:safepoint=trace:safepointtrace.txt\f[R]
4912 Turns off all logging, including warnings and errors, and then enables
4913 messages tagged with \f[CB]safepoint\f[R]using \f[CB]trace\f[R]level to the
4914 file \f[CB]safepointtrace.txt\f[R].
4915 The default configuration doesn\[aq]t apply, because the command line
4916 started with \f[CB]\-Xlog:disable\f[R].
4917 .RS
4918 .RE
4919 .SS Complex \-Xlog Usage Examples
4920 .PP
4921 The following describes a few complex examples of using the
4922 \f[CB]\-Xlog\f[R] option.
4923 .TP
4924 .B \f[CB]\-Xlog:gc+class*=debug\f[R]
4925 Logs messages tagged with at least \f[CB]gc\f[R] and \f[CB]class\f[R] tags
4926 using the \f[CB]debug\f[R] level to \f[CB]stdout\f[R].
4927 The default configuration for all other messages at the level
4928 \f[CB]warning\f[R] is still in effect
4929 .RS
4930 .RE
4931 .TP
4932 .B \f[CB]\-Xlog:gc+meta*=trace,class*=off:file=gcmetatrace.txt\f[R]
4933 Logs messages tagged with at least the \f[CB]gc\f[R] and \f[CB]meta\f[R]
4934 tags using the \f[CB]trace\f[R] level to the file \f[CB]metatrace.txt\f[R]
4935 but turns off all messages tagged with \f[CB]class\f[R].
4936 Messages tagged with \f[CB]gc\f[R], \f[CB]meta\f[R], and \f[CB]class\f[R]
4937 aren\[aq]t be logged as \f[CB]class*\f[R] is set to off.
4938 The default configuration for all other messages at level
4939 \f[CB]warning\f[R] is in effect except for those that include
4940 \f[CB]class\f[R].
4941 .RS
4942 .RE
4943 .TP
4944 .B \f[CB]\-Xlog:gc+meta=trace\f[R]
4945 Logs messages tagged with exactly the \f[CB]gc\f[R] and \f[CB]meta\f[R] tags
4946 using the \f[CB]trace\f[R] level to \f[CB]stdout\f[R].
4947 The default configuration for all other messages at level
4948 \f[CB]warning\f[R] is still be in effect.
4949 .RS
4950 .RE
4951 .TP
4952 .B \f[CB]\-Xlog:gc+class+heap*=debug,meta*=warning,threads*=off\f[R]
4953 Logs messages tagged with at least \f[CB]gc\f[R], \f[CB]class\f[R], and
4954 \f[CB]heap\f[R] tags using the \f[CB]trace\f[R] level to \f[CB]stdout\f[R] but
4955 only log messages tagged with \f[CB]meta\f[R] with level.
4956 The default configuration for all other messages at the level
4957 \f[CB]warning\f[R] is in effect except for those that include
4958 \f[CB]threads\f[R].
4959 .RS
4960 .RE
4961 .SH VALIDATE JAVA VIRTUAL MACHINE FLAG ARGUMENTS
4962 .PP
4963 You use values provided to all Java Virtual Machine (JVM) command\-line
4964 flags for validation and, if the input value is invalid or
4965 out\-of\-range, then an appropriate error message is displayed.
4966 .PP
4967 Whether they\[aq]re set ergonomically, in a command line, by an input
4968 tool, or through the APIs (for example, classes contained in the package
4969 \f[CB]java.lang.management\f[R]) the values provided to all Java Virtual
4970 Machine (JVM) command\-line flags are validated.
4971 Ergonomics are described in Java Platform, Standard Edition HotSpot
4972 Virtual Machine Garbage Collection Tuning Guide.
4973 .PP
4974 Range and constraints are validated either when all flags have their
4975 values set during JVM initialization or a flag\[aq]s value is changed
4976 during runtime (for example using the \f[CB]jcmd\f[R] tool).
4977 The JVM is terminated if a value violates either the range or constraint
4978 check and an appropriate error message is printed on the error stream.
4979 .PP
4980 For example, if a flag violates a range or a constraint check, then the
4981 JVM exits with an error:
4982 .IP
4983 .nf
4984 \f[CB]
4985 java\ \-XX:AllocatePrefetchStyle=5\ \-version\ \ \
4986 intx\ AllocatePrefetchStyle=5\ is\ outside\ the\ allowed\ range\ [\ 0\ ...\ 3\ ]\ \ \
4987 Improperly\ specified\ VM\ option\ \[aq]AllocatePrefetchStyle=5\[aq]\ \ \
4988 Error:\ Could\ not\ create\ the\ Java\ Virtual\ Machine.\ \
4989 Error:\ A\ fatal\ exception\ has\ occurred.\ Program\ will\ exit.
4990 \f[R]
4991 .fi
4992 .PP
4993 The flag \f[CB]\-XX:+PrintFlagsRanges\f[R] prints the range of all the
4994 flags.
4995 This flag allows automatic testing of the flags by the values provided
4996 by the ranges.
4997 For the flags that have the ranges specified, the type, name, and the
4998 actual range is printed in the output.
4999 .PP
5000 For example,
5001 .IP
5002 .nf
5003 \f[CB]
5004 intx\ \ \ ThreadStackSize\ [\ 0\ ...\ 9007199254740987\ ]\ {pd\ product}
5005 \f[R]
5006 .fi
5007 .PP
5008 For the flags that don\[aq]t have the range specified, the values
5009 aren\[aq]t displayed in the print out.
5010 For example:
5011 .IP
5012 .nf
5013 \f[CB]
5014 size_t\ NewSize\ \ \ \ \ \ \ \ \ [\ \ \ ...\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ]\ {product}
5015 \f[R]
5016 .fi
5017 .PP
5018 This helps to identify the flags that need to be implemented.
5019 The automatic testing framework can skip those flags that don\[aq]t have
5020 values and aren\[aq]t implemented.
5021 .SH LARGE PAGES
5022 .PP
5023 You use large pages, also known as huge pages, as memory pages that are
5024 significantly larger than the standard memory page size (which varies
5025 depending on the processor and operating system).
5026 Large pages optimize processor Translation\-Lookaside Buffers.
5027 .PP
5028 A Translation\-Lookaside Buffer (TLB) is a page translation cache that
5029 holds the most\-recently used virtual\-to\-physical address
5030 translations.
5031 A TLB is a scarce system resource.
5032 A TLB miss can be costly because the processor must then read from the
5033 hierarchical page table, which may require multiple memory accesses.
5034 By using a larger memory page size, a single TLB entry can represent a
5035 larger memory range.
5036 This results in less pressure on a TLB, and memory\-intensive
5037 applications may have better performance.
5038 .PP
5039 However, large pages page memory can negatively affect system
5040 performance.
5041 For example, when a large mount of memory is pinned by an application,
5042 it may create a shortage of regular memory and cause excessive paging in
5043 other applications and slow down the entire system.
5044 Also, a system that has been up for a long time could produce excessive
5045 fragmentation, which could make it impossible to reserve enough large
5046 page memory.
5047 When this happens, either the OS or JVM reverts to using regular pages.
5048 .PP
5049 Oracle Solaris, Linux, and Windows support large pages.
5050 .SS Large Pages Support for Oracle Solaris
5051 .PP
5052 Oracle Solaris includes Multiple Page Size Support (MPSS).
5053 No additional configuration is necessary.
5054 .SS Large Pages Support for Linux
5055 .PP
5056 The 2.6 kernel supports large pages.
5057 Some vendors have backported the code to their 2.4\-based releases.
5058 To check if your system can support large page memory, try the
5059 following:
5060 .IP
5061 .nf
5062 \f[CB]
5063 #\ cat\ /proc/meminfo\ |\ grep\ Huge
5064 HugePages_Total:\ 0
5065 HugePages_Free:\ 0
5066 Hugepagesize:\ 2048\ kB
5067 \f[R]
5068 .fi
5069 .PP
5070 If the output shows the three "Huge" variables, then your system can
5071 support large page memory but it needs to be configured.
5072 If the command prints nothing, then your system doesn\[aq]t support
5073 large pages.
5074 To configure the system to use large page memory, login as
5075 \f[CB]root\f[R], and then follow these steps:
5076 .IP "1." 3
5077 If you\[aq]re using the option \f[CB]\-XX:+UseSHM\f[R] (instead of
5078 \f[CB]\-XX:+UseHugeTLBFS\f[R]), then increase the \f[CB]SHMMAX\f[R] value.
5079 It must be larger than the Java heap size.
5080 On a system with 4 GB of physical RAM (or less), the following makes all
5081 the memory sharable:
5082 .RS 4
5083 .RS
5084 .PP
5085 \f[CB]#\ echo\ 4294967295\ >\ /proc/sys/kernel/shmmax\f[R]
5086 .RE
5087 .RE
5088 .IP "2." 3
5089 If you\[aq]re using the option \f[CB]\-XX:+UseSHM\f[R] or
5090 \f[CB]\-XX:+UseHugeTLBFS\f[R], then specify the number of large pages.
5091 In the following example, 3 GB of a 4 GB system are reserved for large
5092 pages (assuming a large page size of 2048kB, then 3 GB = 3 * 1024 MB =
5093 3072 MB = 3072 * 1024 kB = 3145728 kB and 3145728 kB / 2048 kB = 1536):
5094 .RS 4
5095 .RS
5096 .PP
5097 \f[CB]#\ echo\ 1536\ >\ /proc/sys/vm/nr_hugepages\f[R]
5098 .RE
5099 .RS
5100 .PP
5101 \f[B]Note:\f[R] The values contained in \f[CB]/proc\f[R] resets after you
5102 reboot your system, so may want to set them in an initialization script
5103 (for example, \f[CB]rc.local\f[R] or \f[CB]sysctl.conf\f[R]).
5104 .RE
5105 .RE
5106 .IP \[bu] 2
5107 If you configure (or resize) the OS kernel parameters
5108 \f[CB]/proc/sys/kernel/shmmax\f[R] or \f[CB]/proc/sys/vm/nr_hugepages\f[R],
5109 Java processes may allocate large pages for areas in addition to the
5110 Java heap.
5111 These steps can allocate large pages for the following areas:
5112 .RS 2
5113 .IP \[bu] 2
5114 Java heap
5115 .IP \[bu] 2
5116 Code cache
5117 .IP \[bu] 2
5118 The marking bitmap data structure for the parallel GC
5119 .PP
5120 Consequently, if you configure the \f[CB]nr_hugepages\f[R] parameter to
5121 the size of the Java heap, then the JVM can fail in allocating the code
5122 cache areas on large pages because these areas are quite large in size.
5123 .RE
5124 .SS Large Pages Support for Windows
5125 .PP
5126 To use large pages support on Windows, the administrator must first
5127 assign additional privileges to the user who is running the application:
5128 .IP "1." 3
5129 Select \f[B]Control Panel\f[R], \f[B]Administrative Tools\f[R], and then
5130 \f[B]Local Security Policy\f[R].
5131 .IP "2." 3
5132 Select \f[B]Local Policies\f[R] and then \f[B]User Rights Assignment\f[R].
5133 .IP "3." 3
5134 Double\-click \f[B]Lock pages in memory\f[R], then add users and/or
5135 groups.
5136 .IP "4." 3
5137 Reboot your system.
5138 .PP
5139 Note that these steps are required even if it\[aq]s the administrator
5140 who\[aq]s running the application, because administrators by default
5141 don\[aq]t have the privilege to lock pages in memory.
5142 .SH APPLICATION CLASS DATA SHARING
5143 .PP
5144 Application Class Data Sharing (AppCDS) extends class data sharing (CDS)
5145 to enable application classes to be placed in a shared archive.
5146 .PP
5147 In addition to the core library classes, AppCDS supports \f[B]Class Data
5148 Sharing\f[R]
5149 [https://docs.oracle.com/en/java/javase/12/vm/class\-data\-sharing.html#GUID\-7EAA3411\-8CF0\-4D19\-BD05\-DF5E1780AA91]
5150 from the following locations:
5151 .IP \[bu] 2
5152 Platform classes from the runtime image
5153 .IP \[bu] 2
5154 Application classes from the runtime image
5155 .IP \[bu] 2
5156 Application classes from the class path
5157 .IP \[bu] 2
5158 Application classes from the module path
5159 .PP
5160 Archiving application classes provides better start up time at runtime.
5161 When running multiple JVM processes, AppCDS also reduces the runtime
5162 footprint with memory sharing for read\-only metadata.
5163 .PP
5164 CDS/AppCDS supports archiving classes from JAR files only.
5165 .PP
5166 Prior to JDK 11, a non\-empty directory was reported as a fatal error in
5167 the following conditions:
5168 .IP \[bu] 2
5169 For base CDS, a non\-empty directory cannot exist in the
5170 \f[CB]\-Xbootclasspath/a\f[R] path
5171 .IP \[bu] 2
5172 With \f[CB]\-XX:+UseAppCDS\f[R], a non\-empty directory could not exist in
5173 the \f[CB]\-Xbootclasspath/a\f[R] path, class path, and module path.
5174 .PP
5175 In JDK 11 and later, \f[CB]\-XX:+UseAppCDS\f[R] is obsolete and the
5176 behavior for a non\-empty directory is based on the class types in the
5177 classlist.
5178 A non\-empty directory is reported as a fatal error in the following
5179 conditions:
5180 .IP \[bu] 2
5181 If application classes or platform classes are not loaded, dump time
5182 only reports an error if a non\-empty directory exists in
5183 \f[CB]\-Xbootclasspath/a\f[R] path
5184 .IP \[bu] 2
5185 If application classes or platform classes are loaded, dump time reports
5186 an error for a non\-empty directory that exists in
5187 \f[CB]\-Xbootclasspath/a\f[R] path, class path, or module path
5188 .PP
5189 In JDK 11 and later, using
5190 \f[CB]\-XX:DumpLoadedClassList=\f[R]\f[I]class_list_file\f[R] results a
5191 generated classlist with all classes (both system library classes and
5192 application classes) included.
5193 You no longer have to specify \f[CB]\-XX:+UseAppCDS\f[R] with
5194 \f[CB]\-XX:DumpLoadedClassList\f[R] to produce a complete class list.
5195 .PP
5196 In JDK 11 and later, because \f[CB]UseAppCDS\f[R] is obsolete,
5197 \f[CB]SharedArchiveFile\f[R] becomes a product flag by default.
5198 Specifying \f[CB]+UnlockDiagnosticVMOptions\f[R] for
5199 \f[CB]SharedArchiveFile\f[R] is no longer needed in any configuration.
5200 .PP
5201 Class Data Sharing (CDS)/AppCDS does not support archiving array classes
5202 in a class list.
5203 When an array in the class list is encountered, CDS dump time gives the
5204 explicit error message:
5205 .RS
5206 .PP
5207 \f[CB]Preload\ Warning:\ Cannot\ find\f[R] \f[I]array_name\f[R]
5208 .RE
5209 .PP
5210 Although an array in the class list is not allowed, some array classes
5211 can still be created at CDS/AppCDS dump time.
5212 Those arrays are created during the execution of the Java code used by
5213 the Java class loaders (\f[CB]PlatformClassLoader\f[R] and the system
5214 class loader) to load classes at dump time.
5215 The created arrays are archived with the rest of the loaded classes.
5216 .SS Extending Class Data Sharing to Support the Module Path
5217 .PP
5218 In JDK 11, Class Data Sharing (CDS) has been improved to support
5219 archiving classes from the module path.
5220 .IP \[bu] 2
5221 To create a CDS archive using the \f[CB]\-\-module\-path\f[R] VM option,
5222 use the following command line syntax:
5223 .RS 2
5224 .RS
5225 .PP
5226 \f[CB]java\ \-Xshare:dump\ \-XX:SharedClassListFile=\f[R]\f[I]class_list_file\f[R]
5227 \f[CB]\-XX:SharedArchiveFile=\f[R]\f[I]shared_archive_file\f[R]
5228 \f[CB]\-\-module\-path=\f[R]\f[I]path_to_modular_jar\f[R] \f[CB]\-m\f[R]
5229 \f[I]module_name\f[R]
5230 .RE
5231 .RE
5232 .IP \[bu] 2
5233 To run with a CDS archive using the \f[CB]\-\-module\-path\f[R] VM option,
5234 use the following the command line syntax:
5235 .RS 2
5236 .RS
5237 .PP
5238 \f[CB]java\ \-XX:SharedArchiveFile=\f[R]\f[I]shared_archive_file\f[R]
5239 \f[CB]\-\-module\-path=\f[R]\f[I]path_to_modular_jar\f[R] \f[CB]\-m\f[R]
5240 \f[I]module_name\f[R]
5241 .RE
5242 .RE
5243 .PP
5244 The following table describes how the VM options related to module paths
5245 can be used along with the \f[CB]\-Xshare\f[R] option.
5246 .PP
5247 .TS
5248 tab(@);
5249 l l l.
5250 T{
5251 Option
5252 T}@T{
5253 \-Xshare:dump
5254 T}@T{
5255 \-Xshare:{on,auto}
5256 T}
5257 _
5258 T{
5259 \f[CB]\-\-module\-path\f[R][1] \f[I]mp\f[R]
5260 T}@T{
5261 Allowed
5262 T}@T{
5263 Allowed[2]
5264 T}
5265 T{
5266 \f[CB]\-\-module\f[R]
5267 T}@T{
5268 Allowed
5269 T}@T{
5270 Allowed
5271 T}
5272 T{
5273 \f[CB]\-\-add\-module\f[R]
5274 T}@T{
5275 Allowed
5276 T}@T{
5277 Allowed
5278 T}
5279 T{
5280 \f[CB]\-\-upgrade\-module\-path\f[R][3]
5281 T}@T{
5282 Disallowed (exits if specified)
5283 T}@T{
5284 Allowed (disables CDS)
5285 T}
5286 T{
5287 \f[CB]\-\-patch\-module\f[R][4]
5288 T}@T{
5289 Disallowed (exits if specified)
5290 T}@T{
5291 Allowed (disables CDS)
5292 T}
5293 T{
5294 \f[CB]\-\-limit\-modules\f[R][5]
5295 T}@T{
5296 Disallowed (exits if specified)
5297 T}@T{
5298 Allowed (disables CDS)
5299 T}
5300 .TE
5301 .PP
5302 [1] Although there are two ways of specifying a module in a
5303 \f[CB]\-\-module\-path\f[R], that is, modular JAR or exploded module, only
5304 modular JARs are supported.
5305 .PP
5306 [2] Different \f[I]mp\f[R] can be specified during dump time versus run
5307 time.
5308 If an archived class K was loaded from \f[CB]mp1.jar\f[R] at dump time,
5309 but changes in \f[I]mp\f[R] cause it to be available from a different
5310 \f[CB]mp2.jar\f[R] at run time, then the archived version of K will be
5311 disregarded at run time; K will be loaded dynamically.
5312 .PP
5313 [3] Currently, only two system modules are upgradeable
5314 (\f[CB]java.compiler\f[R] and \f[CB]jdk.internal.vm.compiler\f[R]).
5315 However, these modules are seldom upgraded in production software.
5316 .PP
5317 [4] As documented in JEP 261, using \f[CB]\-\-patch\-module\f[R] is
5318 strongly discouraged for production use.
5319 .PP
5320 [5] \f[CB]\-\-limit\-modules\f[R] is intended for testing purposes.
5321 It is seldom used in production software.
5322 .PP
5323 If \f[CB]\-\-upgrade\-module\-path\f[R], \f[CB]\-\-patch\-module\f[R], or
5324 \f[CB]\-\-limit\-modules\f[R] is specified at dump time, an error will be
5325 printed and the JVM will exit.
5326 For example, if the \f[CB]\-\-limit\-modules\f[R] option is specified at
5327 dump time, the user will see the following error:
5328 .IP
5329 .nf
5330 \f[CB]
5331 Error\ occurred\ during\ initialization\ of\ VM
5332 Cannot\ use\ the\ following\ option\ when\ dumping\ the\ shared\ archive:\ \-\-limit\-modules
5333 \f[R]
5334 .fi
5335 .PP
5336 If \f[CB]\-\-upgrade\-module\-path\f[R], \f[CB]\-\-patch\-module\f[R], or
5337 \f[CB]\-\-limit\-modules\f[R] is specified at run time, a warning message
5338 will be printed indicating that CDS is disabled.
5339 For example, if the \f[CB]\-\-limit\-modules\f[R] options is specified at
5340 run time, the user will see the following warning:
5341 .IP
5342 .nf
5343 \f[CB]
5344 Java\ HotSpot(TM)\ 64\-Bit\ Server\ VM\ warning:\ CDS\ is\ disabled\ when\ the\ \-\-limit\-modules\ option\ is\ specified.
5345 \f[R]
5346 .fi
5347 .PP
5348 Several other noteworthy things include:
5349 .IP \[bu] 2
5350 Any valid combinations of \f[CB]\-cp\f[R] and \f[CB]\-\-module\-path\f[R]
5351 are supported.
5352 .IP \[bu] 2
5353 A non\-empty directory in the module path causes a fatal error.
5354 The user will see the following error messages:
5355 .RS 2
5356 .IP
5357 .nf
5358 \f[CB]
5359 Error:\ non\-empty\ directory\ <directory>\ Hint:\ enable\ \-Xlog:class+path=info\ to\ diagnose\ the\ failure\ Error\ occurred\ during\ initialization\ of\ VM\ Cannot\ have\ non\-empty\ directory\ in\ paths
5360 \f[R]
5361 .fi
5362 .RE
5363 .IP \[bu] 2
5364 Unlike the class path, there\[aq]s no restriction that the module path
5365 at dump time must be equal to or be a prefix of the module path at run
5366 time.
5367 .IP \[bu] 2
5368 The archive is invalidated if an existing JAR in the module path is
5369 updated after archive generation.
5370 .IP \[bu] 2
5371 Removing a JAR from the module path does not invalidate the shared
5372 archive.
5373 Archived classes from the removed JAR are not used at runtime.
5374 .SS Dynamic CDS archive
5375 .PP
5376 Dynamic CDS archive extends AppCDS to allow archiving of classes when a
5377 Java application exits.
5378 It improves the usability of AppCDS by eliminating the trial run step
5379 for creating a class list for each application.
5380 The archived classes include all loaded application classes and library
5381 classes that are not present in the default CDS archive which is
5382 included in the JDK.
5383 .PP
5384 A base archive is required when creating a dynamic archive.
5385 If the base archive is not specified, the default CDS archive is used as
5386 the base archive.
5387 .PP
5388 To create a dynamic CDS archive with the default CDS archive as the base
5389 archive, just add the
5390 \f[CB]\-XX:ArchiveClassesAtExit=<dynamic\ archive>\f[R] option to the
5391 command line for running the Java application.
5392 .PP
5393 If the default CDS archive does not exist, the VM will exit with the
5394 following error:
5395 .IP
5396 .nf
5397 \f[CB]
5398 ArchiveClassesAtExit\ not\ supported\ when\ base\ CDS\ archive\ is\ not\ loaded
5399 \f[R]
5400 .fi
5401 .PP
5402 To run the Java application using a dynamic CDS archive, just add the
5403 \f[CB]\-XX:SharedArchiveFile=<dynamic\ archive>\f[R] option to the command
5404 line for running the Java application.
5405 .PP
5406 The base archive is not required to be specified in the command line.
5407 The base archive information, including its name and full path, will be
5408 retrieved from the dynamic archive header.
5409 Note that the user could also use the \f[CB]\-XX:SharedArchiveFile\f[R]
5410 option for specifying a regular AppCDS archive.
5411 Therefore, the specified archive in the \f[CB]\-XX:SharedArchiveFile\f[R]
5412 option could be either a regular or dynamic archive.
5413 During VM start up the specified archive header will be read.
5414 If \f[CB]\-XX:SharedArchiveFile\f[R] refers to a regular archive, then the
5415 behavior will be unchanged.
5416 If \f[CB]\-XX:SharedArchiveFile\f[R] refers to a dynamic archive, the VM
5417 will retrieve the base archive location from the dynamic archive.
5418 If the dynamic archive was created with the default CDS archive, then
5419 the current default CDS archive will be used, and will be found relative
5420 to the current run time environment.
5421 .PP
5422 Please refer to \f[B]JDK\-8221706\f[R]
5423 [https://bugs.openjdk.java.net/browse/JDK\-8221706] for details on error
5424 checking during dynamic CDS archive dump time and run time.
5425 .SS Creating a Shared Archive File and Using It to Run an Application
5426 .SS AppCDS archive
5427 .PP
5428 The following steps create a shared archive file that contains all the
5429 classes used by the \f[CB]test.Hello\f[R] application.
5430 The last step runs the application with the shared archive file.
5431 .IP "1." 3
5432 Create a list of all classes used by the \f[CB]test.Hello\f[R]
5433 application.
5434 The following command creates a file named \f[CB]hello.classlist\f[R] that
5435 contains a list of all classes used by this application:
5436 .RS 4
5437 .RS
5438 .PP
5439 \f[CB]java\ \-Xshare:off\ \-XX:DumpLoadedClassList=hello.classlist\ \-cp\ hello.jar\ test.Hello\f[R]
5440 .RE
5441 .PP
5442 Note that the classpath specified by the \f[CB]\-cp\f[R] parameter must
5443 contain only JAR files.
5444 .RE
5445 .IP "2." 3
5446 Create a shared archive, named \f[CB]hello.jsa\f[R], that contains all the
5447 classes in \f[CB]hello.classlist\f[R]:
5448 .RS 4
5449 .RS
5450 .PP
5451 \f[CB]java\ \-Xshare:dump\ \-XX:SharedArchiveFile=hello.jsa\ \-XX:SharedClassListFile=hello.classlist\ \-cp\ hello.jar\f[R]
5452 .RE
5453 .PP
5454 Note that the classpath used at archive creation time must be the same
5455 as (or a prefix of) the classpath used at run time.
5456 .RE
5457 .IP "3." 3
5458 Run the application \f[CB]test.Hello\f[R] with the shared archive
5459 \f[CB]hello.jsa\f[R]:
5460 .RS 4
5461 .RS
5462 .PP
5463 \f[CB]java\ \-XX:SharedArchiveFile=hello.jsa\ \-cp\ hello.jar\ test.Hello\f[R]
5464 .RE
5465 .RE
5466 .IP "4." 3
5467 \f[B]Optional\f[R] Verify that the \f[CB]test.Hello\f[R] application is
5468 using the class contained in the \f[CB]hello.jsa\f[R] shared archive:
5469 .RS 4
5470 .RS
5471 .PP
5472 \f[CB]java\ \-XX:SharedArchiveFile=hello.jsa\ \-cp\ hello.jar\ \-verbose:class\ test.Hello\f[R]
5473 .RE
5474 .PP
5475 The output of this command should contain the following text:
5476 .IP
5477 .nf
5478 \f[CB]
5479 Loaded\ test.Hello\ from\ shared\ objects\ file\ by\ sun/misc/Launcher$AppClassLoader
5480 \f[R]
5481 .fi
5482 .RE
5483 .SS Dynamic CDS archive
5484 .PP
5485 The following steps create a dynamic CDS archive file that contains the
5486 classes used by the \f[CB]test.Hello\f[R] application and are not included
5487 in the default CDS archive.
5488 The second step runs the application with the dynamic CDS archive.
5489 .IP "1." 3
5490 Create a dynamic CDS archive, named \f[CB]hello.jsa\f[R], that contains
5491 all the classes in \f[CB]hello.jar\f[R] loaded by the application
5492 \f[CB]test.Hello\f[R]:
5493 .RS 4
5494 .RS
5495 .PP
5496 \f[CB]java\ \-XX:ArchiveClassesAtExit=hello.jsa\ \-cp\ hello.jar\ Hello\f[R]
5497 .RE
5498 .PP
5499 Note that the classpath used at archive creation time must be the same
5500 as (or a prefix of) the classpath used at run time.
5501 .RE
5502 .IP "2." 3
5503 Run the application \f[CB]test.Hello\f[R] with the shared archive
5504 \f[CB]hello.jsa\f[R]:
5505 .RS 4
5506 .RS
5507 .PP
5508 \f[CB]java\ \-XX:SharedArchiveFile=hello.jsa\ \-cp\ hello.jar\ test.Hello\f[R]
5509 .RE
5510 .RE
5511 .IP "3." 3
5512 \f[B]Optional\f[R] Repeat step 4 of the previous section to verify that
5513 the \f[CB]test.Hello\f[R] application is using the class contained in the
5514 \f[CB]hello.jsa\f[R] shared archive.
5515 .PP
5516 To automate the above steps 1 and 2, one can write a script such as the
5517 following:
5518 .IP
5519 .nf
5520 \f[CB]
5521 \ \ \ \ ARCHIVE=hello.jsa
5522 \ \ \ \ if\ test\ \-f\ $ARCHIVE;\ then
5523 \ \ \ \ \ \ \ \ FLAG="\-XX:SharedArchiveFile=$ARCHIVE"
5524 \ \ \ \ else
5525 \ \ \ \ \ \ \ \ FLAG="\-XX:ArchiveClassesAtExit=$ARCHIVE"
5526 \ \ \ \ fi
5527 \ \ \ \ $JAVA_HOME/bin/java\ \-cp\ hello.jar\ $FLAG\ test.Hello
5528 \f[R]
5529 .fi
5530 .PP
5531 Like an AppCDS archive, the archive needs to be re\-generated if the
5532 Java version has changed.
5533 The above script could be adjusted to account for the Java version as
5534 follows:
5535 .IP
5536 .nf
5537 \f[CB]
5538 \ \ \ \ ARCHIVE=hello.jsa
5539 \ \ \ \ VERSION=foo.version
5540 \ \ \ \ if\ test\ \-f\ $ARCHIVE\ \-a\ \-f\ $VERSION\ &&\ cmp\ \-s\ $VERSION\ $JAVA_HOME/release;\ then
5541 \ \ \ \ \ \ \ \ FLAG="\-XX:SharedArchiveFile=$ARCHIVE"
5542 \ \ \ \ else
5543 \ \ \ \ \ \ \ \ FLAG="\-XX:ArchiveClassesAtExit=$ARCHIVE"
5544 \ \ \ \ \ \ \ \ cp\ \-f\ $JAVA_HOME/release\ $VERSION
5545 \ \ \ \ fi
5546 \ \ \ \ $JAVA_HOME/bin/java\ \-cp\ hello.jar\ $FLAG\ test.Hello
5547 \f[R]
5548 .fi
5549 .PP
5550 Currently, we don\[aq]t support concurrent dumping operations to the
5551 same CDS archive.
5552 Care should be taken to avoid multiple writers to the same CDS archive.
5553 .PP
5554 The user could also create a dynamic CDS archive with a specific base
5555 archive, e.g.
5556 named as \f[CB]base.jsa\f[R] as follows:
5557 .RS
5558 .PP
5559 \f[CB]java\ \-XX:SharedArchiveFile=base.jsa\ \-XX:ArchiveClassesAtExit=hello.jsa\ \-cp\ hello.jar\ Hello\f[R]
5560 .RE
5561 .PP
5562 To run the application using the dynamic CDS archive \f[CB]hello.jsa\f[R]
5563 and a specific base CDS archive \f[CB]base.jsa\f[R]:
5564 .RS
5565 .PP
5566 \f[CB]java\ \-XX:SharedArchiveFile=base.jsa:hello.jsa\ \-cp\ hello.jar\ Hello\f[R]
5567 .RE
5568 .PP
5569 Note that on Windows, the above path delimiter \f[CB]:\f[R] should be
5570 replaced with \f[CB];\f[R].
5571 .PP
5572 The above command for specifying a base archive is useful if the base
5573 archive used for creating the dynamic archive has been moved.
5574 Normally, just specifying the dynamic archive should be sufficient since
5575 the base archive info can be retrieved from the dynamic archive header.
5576 .SS Sharing a Shared Archive Across Multiple Application Processes
5577 .PP
5578 You can share the same archive file across multiple applications
5579 processes.
5580 This reduces memory usage because the archive is memory\-mapped into the
5581 address space of the processes.
5582 The operating system automatically shares the read\-only pages across
5583 these processes.
5584 .PP
5585 The following steps demonstrate how to create a common archive that can
5586 be shared by different applications.
5587 Classes from \f[CB]common.jar\f[R], \f[CB]hello.jar\f[R] and \f[CB]hi.jar\f[R]
5588 are archived in the \f[CB]common.jsa\f[R] because they are all in the
5589 classpath during the archiving step (step 3).
5590 .PP
5591 To include classes from \f[CB]hello.jar\f[R] and \f[CB]hi.jar\f[R], the
5592 \f[CB]\&.jar\f[R] files must be added to the classpath specified by the
5593 \f[CB]\-cp\f[R] parameter.
5594 .IP "1." 3
5595 Create a list of all classes used by the \f[CB]Hello\f[R] application and
5596 another list for the \f[CB]Hi\f[R] application:
5597 .RS 4
5598 .RS
5599 .PP
5600 \f[CB]java\ \-XX:DumpLoadedClassList=hello.classlist\ \-cp\ common.jar:hello.jar\ Hello\f[R]
5601 .RE
5602 .RS
5603 .PP
5604 \f[CB]java\ \-XX:DumpLoadedClassList=hi.classlist\ \-cp\ common.jar:hi.jar\ Hi\f[R]
5605 .RE
5606 .RE
5607 .IP "2." 3
5608 Create a single list of classes used by all the applications that will
5609 share the shared archive file.
5610 .RS 4
5611 .PP
5612 \f[B]Oracle Solaris, Linux, and macOS\f[R] The following commands combine
5613 the files \f[CB]hello.classlist\f[R] and \f[CB]hi.classlist\f[R] into one
5614 file, \f[CB]common.classlist\f[R]:
5615 .RS
5616 .PP
5617 \f[CB]cat\ hello.classlist\ hi.classlist\ >\ common.classlist\f[R]
5618 .RE
5619 .PP
5620 \f[B]Windows\f[R] The following commands combine the files
5621 \f[CB]hello.classlist\f[R] and \f[CB]hi.classlist\f[R] into one file,
5622 \f[CB]common.classlist\f[R]:
5623 .RS
5624 .PP
5625 \f[CB]type\ hello.classlist\ hi.classlist\ >\ common.classlist\f[R]
5626 .RE
5627 .RE
5628 .IP "3." 3
5629 Create a shared archive named \f[CB]common.jsa\f[R] that contains all the
5630 classes in \f[CB]common.classlist\f[R]:
5631 .RS 4
5632 .RS
5633 .PP
5634 \f[CB]java\ \-Xshare:dump\ \-XX:SharedArchiveFile=common.jsa\ \-XX:SharedClassListFile=common.classlist\ \-cp\ common.jar:hello.jar:hi.jar\f[R]
5635 .RE
5636 .PP
5637 The classpath parameter used is the common class path prefix shared by
5638 the \f[CB]Hello\f[R] and \f[CB]Hi\f[R] applications.
5639 .RE
5640 .IP "4." 3
5641 Run the \f[CB]Hello\f[R] and \f[CB]Hi\f[R] applications with the same shared
5642 archive:
5643 .RS 4
5644 .RS
5645 .PP
5646 \f[CB]java\ \-XX:SharedArchiveFile=common.jsa\ \-cp\ common.jar:hello.jar:hi.jar\ Hello\f[R]
5647 .RE
5648 .RS
5649 .PP
5650 \f[CB]java\ \-XX:SharedArchiveFile=common.jsa\ \-cp\ common.jar:hello.jar:hi.jar\ Hi\f[R]
5651 .RE
5652 .RE
5653 .SS Specifying Additional Shared Data Added to an Archive File
5654 .PP
5655 The \f[CB]SharedArchiveConfigFile\f[R] option is used to specify
5656 additional shared data to add to the archive file.
5657 .RS
5658 .PP
5659 \f[CB]\-XX:SharedArchiveConfigFile=\f[R]\f[I]shared_config_file\f[R]
5660 .RE
5661 .PP
5662 JDK 9 and later supports adding both symbols and\ string objects to an
5663 archive for memory sharing\ when you have multiple JVM processes running
5664 on the same host.
5665 An example of this is having multiple JVM processes that use the same
5666 set of Java EE classes.
5667 When these common classes are loaded and used, new symbols and strings
5668 may be created and added to the JVM\[aq]s internal "symbol" and "string"
5669 tables.\ At runtime, the symbols or string objects mapped from the
5670 archive file can be shared across multiple JVM processes, resulting in a
5671 reduction of overall memory usage.\ In addition, archiving strings also
5672 provides added performance benefits in both startup time and runtime
5673 execution.
5674 .PP
5675 In JDK 10 and later, CONSTANT_String entries in archived classes are
5676 resolved to interned String objects at dump time, and all interned
5677 String objects are archived.
5678 However, even though all CONSTANT_String literals in all archived
5679 classes are resolved, it might still beneficial to add additional
5680 strings that are not string literals in class files, but are likely to
5681 be used by your application at run time.
5682 .PP
5683 Symbol data should be generated by the \f[CB]jcmd\f[R] tool attaching to a
5684 running JVM process.
5685 See \f[B]jcmd\f[R].
5686 .PP
5687 The following is an example of the symbol dumping command in
5688 \f[CB]jcmd\f[R]:\
5689 .RS
5690 .PP
5691 \f[CB]jcmd\f[R] \f[I]pid\f[R] \f[CB]VM.symboltable\ \-verbose\f[R]
5692 .RE
5693 .RS
5694 .PP
5695 \f[B]Note:\f[R] The first line (process ID) and the second line
5696 (\f[CB]\@VERSION\ ...\f[R]) of this \f[CB]jcmd\f[R] output should be
5697 excluded from the configuration file.
5698 .RE
5699 .SS Example of a Configuration File
5700 .PP
5701 The following is an example of a configuration file:
5702 .IP
5703 .nf
5704 \f[CB]
5705 VERSION:\ 1.0
5706 \@SECTION:\ Symbol
5707 10\ \-1:\ linkMethod
5708 \f[R]
5709 .fi
5710 .PP
5711 In the configuration file example, the \f[CB]\@SECTION:\ Symbol\f[R] entry
5712 uses the following format:
5713 .RS
5714 .PP
5715 \f[I]length\f[R] \f[I]refcount\f[R]\f[CB]:\f[R] \f[I]symbol\f[R]
5716 .RE
5717 .PP
5718 The \f[I]refcount\f[R] for a shared symbol is always \f[CB]\-1\f[R].
5719 .PP
5720 \f[CB]\@SECTION\f[R] specifies the type of the section that follows it.
5721 All data within the section must be the same type that\[aq]s specified
5722 by \f[CB]\@SECTION\f[R].
5723 Different types of data can\[aq]t be mixed.
5724 Multiple separated data sections for the same type specified by
5725 different \f[CB]\@SECTION\f[R] are allowed within one
5726 \f[CB]shared_config_file\f[R] .
5727 .SH PERFORMANCE TUNING EXAMPLES
5728 .PP
5729 You can use the Java advanced runtime options to optimize the
5730 performance of your applications.
5731 .SS Tuning for Higher Throughput
5732 .PP
5733 Use the following commands and advanced options to achieve higher
5734 throughput performance for your application:
5735 .RS
5736 .PP
5737 \f[CB]java\ \-server\ \-XX:+UseParallelGC\ \-XX:+UseLargePages\ \-Xmn10g\ \ \-Xms26g\ \-Xmx26g\f[R]
5738 .RE
5739 .SS Tuning for Lower Response Time
5740 .PP
5741 Use the following commands and advanced options to achieve lower
5742 response times for your application:
5743 .RS
5744 .PP
5745 \f[CB]java\ \-XX:+UseG1GC\ \-XX:MaxGCPauseMillis=100\f[R]
5746 .RE
5747 .SS Keeping the Java Heap Small and Reducing the Dynamic Footprint of
5748 Embedded Applications
5749 .PP
5750 Use the following advanced runtime options to keep the Java heap small
5751 and reduce the dynamic footprint of embedded applications:
5752 .RS
5753 .PP
5754 \f[CB]\-XX:MaxHeapFreeRatio=10\ \-XX:MinHeapFreeRatio=5\f[R]
5755 .RE
5756 .RS
5757 .PP
5758 \f[B]Note:\f[R] The defaults for these two options are 70% and 40%
5759 respectively.
5760 Because performance sacrifices can occur when using these small
5761 settings, you should optimize for a small footprint by reducing these
5762 settings as much as possible without introducing unacceptable
5763 performance degradation.
5764 .RE
5765 .SH EXIT STATUS
5766 .PP
5767 The following exit values are typically returned by the launcher when
5768 the launcher is called with the wrong arguments, serious errors, or
5769 exceptions thrown by the JVM.
5770 However, a Java application may choose to return any value by using the
5771 API call \f[CB]System.exit(exitValue)\f[R].
5772 The values are:
5773 .IP \[bu] 2
5774 \f[CB]0\f[R]: Successful completion
5775 .IP \[bu] 2
5776 \f[CB]>0\f[R]: An error occurred