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22 .\"
23 .\" Title: java
24 .\" Language: English
25 .\" Date: 03 March 2015
26 .\" SectDesc: Basic Tools
27 .\" Software: JDK 8
28 .\" Arch: generic
29 .\" Part Number: E38207-04
30 .\" Doc ID: JSSON
31 .\"
32 .if n .pl 99999
33 .TH "java" "1" "03 March 2015" "JDK 8" "Basic Tools"
34 .\" -----------------------------------------------------------------
35 .\" * Define some portability stuff
36 .\" -----------------------------------------------------------------
37 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
38 .\" http://bugs.debian.org/507673
39 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
40 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
41 .ie \n(.g .ds Aq \(aq
42 .el .ds Aq '
43 .\" -----------------------------------------------------------------
44 .\" * set default formatting
45 .\" -----------------------------------------------------------------
46 .\" disable hyphenation
47 .nh
48 .\" disable justification (adjust text to left margin only)
49 .ad l
50 .\" -----------------------------------------------------------------
51 .\" * MAIN CONTENT STARTS HERE *
52 .\" -----------------------------------------------------------------
53 .SH "NAME"
54 java \- Launches a Java application\&.
55 .SH "SYNOPSIS"
56 .sp
57 .if n \{\
58 .RS 4
59 .\}
60 .nf
61 \fBjava\fR [\fIoptions\fR] \fIclassname\fR [\fIargs\fR]
62 .fi
63 .if n \{\
64 .RE
65 .\}
66 .sp
67 .if n \{\
68 .RS 4
69 .\}
70 .nf
71 \fBjava\fR [\fIoptions\fR] \fB\-jar\fR \fIfilename\fR [\fIargs\fR]
72 .fi
73 .if n \{\
74 .RE
75 .\}
76 .PP
77 \fIoptions\fR
78 .RS 4
79 Command\-line options separated by spaces\&. See Options\&.
80 .RE
81 .PP
82 \fIclassname\fR
83 .RS 4
84 The name of the class to be launched\&.
85 .RE
86 .PP
87 \fIfilename\fR
88 .RS 4
89 The name of the Java Archive (JAR) file to be called\&. Used only with the
90 \fB\-jar\fR
91 option\&.
92 .RE
93 .PP
94 \fIargs\fR
95 .RS 4
96 The arguments passed to the
97 \fBmain()\fR
98 method separated by spaces\&.
99 .RE
100 .SH "DESCRIPTION"
101 .PP
102 The
103 \fBjava\fR
104 command starts a Java application\&. It does this by starting the Java Runtime Environment (JRE), loading the specified class, and calling that class\*(Aqs
105 \fBmain()\fR
106 method\&. The method must be declared
107 \fIpublic\fR
108 and
109 \fIstatic\fR, it must not return any value, and it must accept a
110 \fBString\fR
111 array as a parameter\&. The method declaration has the following form:
112 .sp
113 .if n \{\
114 .RS 4
115 .\}
116 .nf
117 \fBpublic static void main(String[] args)\fR
118
119 .fi
120 .if n \{\
121 .RE
122 .\}
123 .PP
124 The
125 \fBjava\fR
126 command can be used to launch a JavaFX application by loading a class that either has a
127 \fBmain()\fR
128 method or that extends
129 \fBjavafx\&.application\&.Application\fR\&. In the latter case, the launcher constructs an instance of the
130 \fBApplication\fR
131 class, calls its
132 \fBinit()\fR
133 method, and then calls the
134 \fBstart(javafx\&.stage\&.Stage)\fR
135 method\&.
136 .PP
137 By default, the first argument that is not an option of the
138 \fBjava\fR
139 command is the fully qualified name of the class to be called\&. If the
140 \fB\-jar\fR
141 option is specified, its argument is the name of the JAR file containing class and resource files for the application\&. The startup class must be indicated by the
142 \fBMain\-Class\fR
143 manifest header in its source code\&.
144 .PP
145 The JRE searches for the startup class (and other classes used by the application) in three sets of locations: the bootstrap class path, the installed extensions, and the user\(cqs class path\&.
146 .PP
147 Arguments after the class file name or the JAR file name are passed to the
148 \fBmain()\fR
149 method\&.
150 .SH "OPTIONS"
151 .PP
152 The
153 \fBjava\fR
154 command supports a wide range of options that can be divided into the following categories:
155 .sp
156 .RS 4
157 .ie n \{\
158 \h'-04'\(bu\h'+03'\c
159 .\}
160 .el \{\
161 .sp -1
162 .IP \(bu 2.3
163 .\}
164 Standard Options
165 .RE
166 .sp
167 .RS 4
168 .ie n \{\
169 \h'-04'\(bu\h'+03'\c
170 .\}
171 .el \{\
172 .sp -1
173 .IP \(bu 2.3
174 .\}
175 Non\-Standard Options
176 .RE
177 .sp
178 .RS 4
179 .ie n \{\
180 \h'-04'\(bu\h'+03'\c
181 .\}
182 .el \{\
183 .sp -1
184 .IP \(bu 2.3
185 .\}
186 Advanced Runtime Options
187 .RE
188 .sp
189 .RS 4
190 .ie n \{\
191 \h'-04'\(bu\h'+03'\c
192 .\}
193 .el \{\
194 .sp -1
195 .IP \(bu 2.3
196 .\}
197 Advanced JIT Compiler Options
198 .RE
199 .sp
200 .RS 4
201 .ie n \{\
202 \h'-04'\(bu\h'+03'\c
203 .\}
204 .el \{\
205 .sp -1
206 .IP \(bu 2.3
207 .\}
208 Advanced Serviceability Options
209 .RE
210 .sp
211 .RS 4
212 .ie n \{\
213 \h'-04'\(bu\h'+03'\c
214 .\}
215 .el \{\
216 .sp -1
217 .IP \(bu 2.3
218 .\}
219 Advanced Garbage Collection Options
220 .RE
221 .PP
222 Standard options are guaranteed to be supported by all implementations of the Java Virtual Machine (JVM)\&. They are used for common actions, such as checking the version of the JRE, setting the class path, enabling verbose output, and so on\&.
223 .PP
224 Non\-standard options are general purpose options that are specific to the Java HotSpot Virtual Machine, so they are not guaranteed to be supported by all JVM implementations, and are subject to change\&. These options start with
225 \fB\-X\fR\&.
226 .PP
227 Advanced options are not recommended for casual use\&. These are developer options used for tuning specific areas of the Java HotSpot Virtual Machine operation that often have specific system requirements and may require privileged access to system configuration parameters\&. They are also not guaranteed to be supported by all JVM implementations, and are subject to change\&. Advanced options start with
228 \fB\-XX\fR\&.
229 .PP
230 To keep track of the options that were deprecated or removed in the latest release, there is a section named Deprecated and Removed Options at the end of the document\&.
231 .PP
232 Boolean options are used to either enable a feature that is disabled by default or disable a feature that is enabled by default\&. Such options do not require a parameter\&. Boolean
233 \fB\-XX\fR
234 options are enabled using the plus sign (\fB\-XX:+\fR\fIOptionName\fR) and disabled using the minus sign (\fB\-XX:\-\fR\fIOptionName\fR)\&.
235 .PP
236 For options that require an argument, the argument may be separated from the option name by a space, a colon (:), or an equal sign (=), or the argument may directly follow the option (the exact syntax differs for each option)\&. If you are expected to specify the size in bytes, you can use no suffix, or use the suffix
237 \fBk\fR
238 or
239 \fBK\fR
240 for kilobytes (KB),
241 \fBm\fR
242 or
243 \fBM\fR
244 for megabytes (MB),
245 \fBg\fR
246 or
247 \fBG\fR
248 for gigabytes (GB)\&. For example, to set the size to 8 GB, you can specify either
249 \fB8g\fR,
250 \fB8192m\fR,
251 \fB8388608k\fR, or
252 \fB8589934592\fR
253 as the argument\&. If you are expected to specify the percentage, use a number from 0 to 1 (for example, specify
254 \fB0\&.25\fR
255 for 25%)\&.
256 .SS "Standard Options"
257 .PP
258 These are the most commonly used options that are supported by all implementations of the JVM\&.
259 .PP
260 \-agentlib:\fIlibname\fR[=\fIoptions\fR]
261 .RS 4
262 Loads the specified native agent library\&. After the library name, a comma\-separated list of options specific to the library can be used\&.
263 .sp
264 If the option
265 \fB\-agentlib:foo\fR
266 is specified, then the JVM attempts to load the library named
267 \fBlibfoo\&.so\fR
268 in the location specified by the
269 \fBLD_LIBRARY_PATH\fR
270 system variable (on OS X this variable is
271 \fBDYLD_LIBRARY_PATH\fR)\&.
272 .sp
273 The following example shows how to load the heap profiling tool (HPROF) library and get sample CPU information every 20 ms, with a stack depth of 3:
274 .sp
275 .if n \{\
276 .RS 4
277 .\}
278 .nf
279 \fB\-agentlib:hprof=cpu=samples,interval=20,depth=3\fR
280
281 .fi
282 .if n \{\
283 .RE
284 .\}
285 The following example shows how to load the Java Debug Wire Protocol (JDWP) library and listen for the socket connection on port 8000, suspending the JVM before the main class loads:
286 .sp
287 .if n \{\
288 .RS 4
289 .\}
290 .nf
291 \fB\-agentlib:jdwp=transport=dt_socket,server=y,address=8000\fR
292
293 .fi
294 .if n \{\
295 .RE
296 .\}
297 For more information about the native agent libraries, refer to the following:
298 .sp
299 .RS 4
300 .ie n \{\
301 \h'-04'\(bu\h'+03'\c
302 .\}
303 .el \{\
304 .sp -1
305 .IP \(bu 2.3
306 .\}
307 The
308 \fBjava\&.lang\&.instrument\fR
309 package description at http://docs\&.oracle\&.com/javase/8/docs/api/java/lang/instrument/package\-summary\&.html
310 .RE
311 .sp
312 .RS 4
313 .ie n \{\
314 \h'-04'\(bu\h'+03'\c
315 .\}
316 .el \{\
317 .sp -1
318 .IP \(bu 2.3
319 .\}
320 Agent Command Line Options in the JVM Tools Interface guide at http://docs\&.oracle\&.com/javase/8/docs/platform/jvmti/jvmti\&.html#starting
321 .RE
322 .RE
323 .PP
324 \-agentpath:\fIpathname\fR[=\fIoptions\fR]
325 .RS 4
326 Loads the native agent library specified by the absolute path name\&. This option is equivalent to
327 \fB\-agentlib\fR
328 but uses the full path and file name of the library\&.
329 .RE
330 .PP
331 \-client
332 .RS 4
333 Selects the Java HotSpot Client VM\&. The 64\-bit version of the Java SE Development Kit (JDK) currently ignores this option and instead uses the Server JVM\&.
334 .sp
335 For default JVM selection, see Server\-Class Machine Detection at
336 http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/server\-class\&.html
337 .RE
338 .PP
339 \-D\fIproperty\fR=\fIvalue\fR
340 .RS 4
341 Sets a system property value\&. The
342 \fIproperty\fR
343 variable is a string with no spaces that represents the name of the property\&. The
344 \fIvalue\fR
345 variable is a string that represents the value of the property\&. If
346 \fIvalue\fR
347 is a string with spaces, then enclose it in quotation marks (for example
348 \fB\-Dfoo="foo bar"\fR)\&.
349 .RE
350 .PP
351 \-d32
352 .RS 4
353 Runs the application in a 32\-bit environment\&. If a 32\-bit environment is not installed or is not supported, then an error will be reported\&. By default, the application is run in a 32\-bit environment unless a 64\-bit system is used\&.
354 .RE
355 .PP
356 \-d64
357 .RS 4
358 Runs the application in a 64\-bit environment\&. If a 64\-bit environment is not installed or is not supported, then an error will be reported\&. By default, the application is run in a 32\-bit environment unless a 64\-bit system is used\&.
359 .sp
360 Currently only the Java HotSpot Server VM supports 64\-bit operation, and the
361 \fB\-server\fR
362 option is implicit with the use of
363 \fB\-d64\fR\&. The
364 \fB\-client\fR
365 option is ignored with the use of
366 \fB\-d64\fR\&. This is subject to change in a future release\&.
367 .RE
368 .PP
369 \-disableassertions[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR]
370 .br
371 \-da[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR]
372 .RS 4
373 Disables assertions\&. By default, assertions are disabled in all packages and classes\&.
374 .sp
375 With no arguments,
376 \fB\-disableassertions\fR
377 (\fB\-da\fR) disables assertions in all packages and classes\&. With the
378 \fIpackagename\fR
379 argument ending in
380 \fB\&.\&.\&.\fR, the switch disables assertions in the specified package and any subpackages\&. If the argument is simply
381 \fB\&.\&.\&.\fR, then the switch disables assertions in the unnamed package in the current working directory\&. With the
382 \fIclassname\fR
383 argument, the switch disables assertions in the specified class\&.
384 .sp
385 The
386 \fB\-disableassertions\fR
387 (\fB\-da\fR) option applies to all class loaders and to system classes (which do not have a class loader)\&. There is one exception to this rule: if the option is provided with no arguments, then it does not apply to system classes\&. This makes it easy to disable assertions in all classes except for system classes\&. The
388 \fB\-disablesystemassertions\fR
389 option enables you to disable assertions in all system classes\&.
390 .sp
391 To explicitly enable assertions in specific packages or classes, use the
392 \fB\-enableassertions\fR
393 (\fB\-ea\fR) option\&. Both options can be used at the same time\&. For example, to run the
394 \fBMyClass\fR
395 application with assertions enabled in package
396 \fBcom\&.wombat\&.fruitbat\fR
397 (and any subpackages) but disabled in class
398 \fBcom\&.wombat\&.fruitbat\&.Brickbat\fR, use the following command:
399 .sp
400 .if n \{\
401 .RS 4
402 .\}
403 .nf
404 \fBjava \-ea:com\&.wombat\&.fruitbat\&.\&.\&. \-da:com\&.wombat\&.fruitbat\&.Brickbat MyClass\fR
405
406 .fi
407 .if n \{\
408 .RE
409 .\}
410 .RE
411 .PP
412 \-disablesystemassertions
413 .br
414 \-dsa
415 .RS 4
416 Disables assertions in all system classes\&.
417 .RE
418 .PP
419 \-enableassertions[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR]
420 .br
421 \-ea[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR]
422 .RS 4
423 Enables assertions\&. By default, assertions are disabled in all packages and classes\&.
424 .sp
425 With no arguments,
426 \fB\-enableassertions\fR
427 (\fB\-ea\fR) enables assertions in all packages and classes\&. With the
428 \fIpackagename\fR
429 argument ending in
430 \fB\&.\&.\&.\fR, the switch enables assertions in the specified package and any subpackages\&. If the argument is simply
431 \fB\&.\&.\&.\fR, then the switch enables assertions in the unnamed package in the current working directory\&. With the
432 \fIclassname\fR
433 argument, the switch enables assertions in the specified class\&.
434 .sp
435 The
436 \fB\-enableassertions\fR
437 (\fB\-ea\fR) option applies to all class loaders and to system classes (which do not have a class loader)\&. There is one exception to this rule: if the option is provided with no arguments, then it does not apply to system classes\&. This makes it easy to enable assertions in all classes except for system classes\&. The
438 \fB\-enablesystemassertions\fR
439 option provides a separate switch to enable assertions in all system classes\&.
440 .sp
441 To explicitly disable assertions in specific packages or classes, use the
442 \fB\-disableassertions\fR
443 (\fB\-da\fR) option\&. If a single command contains multiple instances of these switches, then they are processed in order before loading any classes\&. For example, to run the
444 \fBMyClass\fR
445 application with assertions enabled only in package
446 \fBcom\&.wombat\&.fruitbat\fR
447 (and any subpackages) but disabled in class
448 \fBcom\&.wombat\&.fruitbat\&.Brickbat\fR, use the following command:
449 .sp
450 .if n \{\
451 .RS 4
452 .\}
453 .nf
454 \fBjava \-ea:com\&.wombat\&.fruitbat\&.\&.\&. \-da:com\&.wombat\&.fruitbat\&.Brickbat MyClass\fR
455
456 .fi
457 .if n \{\
458 .RE
459 .\}
460 .RE
461 .PP
462 \-enablesystemassertions
463 .br
464 \-esa
465 .RS 4
466 Enables assertions in all system classes\&.
467 .RE
468 .PP
469 \-help
470 .br
471 \-?
472 .RS 4
473 Displays usage information for the
474 \fBjava\fR
475 command without actually running the JVM\&.
476 .RE
477 .PP
478 \-jar \fIfilename\fR
479 .RS 4
480 Executes a program encapsulated in a JAR file\&. The
481 \fIfilename\fR
482 argument is the name of a JAR file with a manifest that contains a line in the form
483 \fBMain\-Class:\fR\fIclassname\fR
484 that defines the class with the
485 \fBpublic static void main(String[] args)\fR
486 method that serves as your application\*(Aqs starting point\&.
487 .sp
488 When you use the
489 \fB\-jar\fR
490 option, the specified JAR file is the source of all user classes, and other class path settings are ignored\&.
491 .sp
492 For more information about JAR files, see the following resources:
493 .sp
494 .RS 4
495 .ie n \{\
496 \h'-04'\(bu\h'+03'\c
497 .\}
498 .el \{\
499 .sp -1
500 .IP \(bu 2.3
501 .\}
502 jar(1)
503 .RE
504 .sp
505 .RS 4
506 .ie n \{\
507 \h'-04'\(bu\h'+03'\c
508 .\}
509 .el \{\
510 .sp -1
511 .IP \(bu 2.3
512 .\}
513 The Java Archive (JAR) Files guide at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/jar/index\&.html
514 .RE
515 .sp
516 .RS 4
517 .ie n \{\
518 \h'-04'\(bu\h'+03'\c
519 .\}
520 .el \{\
521 .sp -1
522 .IP \(bu 2.3
523 .\}
524 Lesson: Packaging Programs in JAR Files at
525
526 http://docs\&.oracle\&.com/javase/tutorial/deployment/jar/index\&.html
527 .RE
528 .RE
529 .PP
530 \-javaagent:\fIjarpath\fR[=\fIoptions\fR]
531 .RS 4
532 Loads the specified Java programming language agent\&. For more information about instrumenting Java applications, see the
533 \fBjava\&.lang\&.instrument\fR
534 package description in the Java API documentation at http://docs\&.oracle\&.com/javase/8/docs/api/java/lang/instrument/package\-summary\&.html
535 .RE
536 .PP
537 \-jre\-restrict\-search
538 .RS 4
539 Includes user\-private JREs in the version search\&.
540 .RE
541 .PP
542 \-no\-jre\-restrict\-search
543 .RS 4
544 Excludes user\-private JREs from the version search\&.
545 .RE
546 .PP
547 \-server
548 .RS 4
549 Selects the Java HotSpot Server VM\&. The 64\-bit version of the JDK supports only the Server VM, so in that case the option is implicit\&.
550 .sp
551 For default JVM selection, see Server\-Class Machine Detection at
552 http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/server\-class\&.html
553 .RE
554 .PP
555 \-showversion
556 .RS 4
557 Displays version information and continues execution of the application\&. This option is equivalent to the
558 \fB\-version\fR
559 option except that the latter instructs the JVM to exit after displaying version information\&.
560 .RE
561 .PP
562 \-splash:\fIimgname\fR
563 .RS 4
564 Shows the splash screen with the image specified by
565 \fIimgname\fR\&. For example, to show the
566 \fBsplash\&.gif\fR
567 file from the
568 \fBimages\fR
569 directory when starting your application, use the following option:
570 .sp
571 .if n \{\
572 .RS 4
573 .\}
574 .nf
575 \fB\-splash:images/splash\&.gif\fR
576
577 .fi
578 .if n \{\
579 .RE
580 .\}
581 .RE
582 .PP
583 \-verbose:class
584 .RS 4
585 Displays information about each loaded class\&.
586 .RE
587 .PP
588 \-verbose:gc
589 .RS 4
590 Displays information about each garbage collection (GC) event\&.
591 .RE
592 .PP
593 \-verbose:jni
594 .RS 4
595 Displays information about the use of native methods and other Java Native Interface (JNI) activity\&.
596 .RE
597 .PP
598 \-version
599 .RS 4
600 Displays version information and then exits\&. This option is equivalent to the
601 \fB\-showversion\fR
602 option except that the latter does not instruct the JVM to exit after displaying version information\&.
603 .RE
604 .PP
605 \-version:\fIrelease\fR
606 .RS 4
607 Specifies the release version to be used for running the application\&. If the version of the
608 \fBjava\fR
609 command called does not meet this specification and an appropriate implementation is found on the system, then the appropriate implementation will be used\&.
610 .sp
611 The
612 \fIrelease\fR
613 argument specifies either the exact version string, or a list of version strings and ranges separated by spaces\&. A
614 \fIversion string\fR
615 is the developer designation of the version number in the following form:
616 \fB1\&.\fR\fIx\fR\fB\&.0_\fR\fIu\fR
617 (where
618 \fIx\fR
619 is the major version number, and
620 \fIu\fR
621 is the update version number)\&. A
622 \fIversion range\fR
623 is made up of a version string followed by a plus sign (\fB+\fR) to designate this version or later, or a part of a version string followed by an asterisk (\fB*\fR) to designate any version string with a matching prefix\&. Version strings and ranges can be combined using a space for a logical
624 \fIOR\fR
625 combination, or an ampersand (\fB&\fR) for a logical
626 \fIAND\fR
627 combination of two version strings/ranges\&. For example, if running the class or JAR file requires either JRE 6u13 (1\&.6\&.0_13), or any JRE 6 starting from 6u10 (1\&.6\&.0_10), specify the following:
628 .sp
629 .if n \{\
630 .RS 4
631 .\}
632 .nf
633 \fB\-version:"1\&.6\&.0_13 1\&.6* & 1\&.6\&.0_10+"\fR
634
635 .fi
636 .if n \{\
637 .RE
638 .\}
639 Quotation marks are necessary only if there are spaces in the
640 \fIrelease\fR
641 parameter\&.
642 .sp
643 For JAR files, the preference is to specify version requirements in the JAR file manifest rather than on the command line\&.
644 .RE
645 .SS "Non\-Standard Options"
646 .PP
647 These options are general purpose options that are specific to the Java HotSpot Virtual Machine\&.
648 .PP
649 \-X
650 .RS 4
651 Displays help for all available
652 \fB\-X\fR
653 options\&.
654 .RE
655 .PP
656 \-Xbatch
657 .RS 4
658 Disables background compilation\&. By default, the JVM compiles the method as a background task, running the method in interpreter mode until the background compilation is finished\&. The
659 \fB\-Xbatch\fR
660 flag disables background compilation so that compilation of all methods proceeds as a foreground task until completed\&.
661 .sp
662 This option is equivalent to
663 \fB\-XX:\-BackgroundCompilation\fR\&.
664 .RE
665 .PP
666 \-Xbootclasspath:\fIpath\fR
667 .RS 4
668 Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to search for boot class files\&. These are used in place of the boot class files included in the JDK\&.
669 .sp
670 Do not deploy applications that use this option to override a class in
671 \fBrt\&.jar\fR, because this violates the JRE binary code license\&.
672 .RE
673 .PP
674 \-Xbootclasspath/a:\fIpath\fR
675 .RS 4
676 Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to append to the end of the default bootstrap class path\&.
677 .sp
678 Do not deploy applications that use this option to override a class in
679 \fBrt\&.jar\fR, because this violates the JRE binary code license\&.
680 .RE
681 .PP
682 \-Xbootclasspath/p:\fIpath\fR
683 .RS 4
684 Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to prepend to the front of the default bootstrap class path\&.
685 .sp
686 Do not deploy applications that use this option to override a class in
687 \fBrt\&.jar\fR, because this violates the JRE binary code license\&.
688 .RE
689 .PP
690 \-Xcheck:jni
691 .RS 4
692 Performs additional checks for Java Native Interface (JNI) functions\&. Specifically, it validates the parameters passed to the JNI function and the runtime environment data before processing the JNI request\&. Any invalid data encountered indicates a problem in the native code, and the JVM will terminate with an irrecoverable error in such cases\&. Expect a performance degradation when this option is used\&.
693 .RE
694 .PP
695 \-Xcomp
696 .RS 4
697 Forces compilation of methods on first invocation\&. By default, the Client VM (\fB\-client\fR) performs 1,000 interpreted method invocations and the Server VM (\fB\-server\fR) performs 10,000 interpreted method invocations to gather information for efficient compilation\&. Specifying the
698 \fB\-Xcomp\fR
699 option disables interpreted method invocations to increase compilation performance at the expense of efficiency\&.
700 .sp
701 You can also change the number of interpreted method invocations before compilation using the
702 \fB\-XX:CompileThreshold\fR
703 option\&.
704 .RE
705 .PP
706 \-Xdebug
707 .RS 4
708 Does nothing\&. Provided for backward compatibility\&.
709 .RE
710 .PP
711 \-Xdiag
712 .RS 4
713 Shows additional diagnostic messages\&.
714 .RE
715 .PP
716 \-Xfuture
717 .RS 4
718 Enables strict class\-file format checks that enforce close conformance to the class\-file format specification\&. Developers are encouraged to use this flag when developing new code because the stricter checks will become the default in future releases\&.
719 .RE
720 .PP
721 \-Xint
722 .RS 4
723 Runs the application in interpreted\-only mode\&. Compilation to native code is disabled, and all bytecode is executed by the interpreter\&. The performance benefits offered by the just in time (JIT) compiler are not present in this mode\&.
724 .RE
725 .PP
726 \-Xinternalversion
727 .RS 4
728 Displays more detailed JVM version information than the
729 \fB\-version\fR
730 option, and then exits\&.
731 .RE
732 .PP
733 \-Xloggc:\fIfilename\fR
734 .RS 4
735 Sets the file to which verbose GC events information should be redirected for logging\&. The information written to this file is similar to the output of
736 \fB\-verbose:gc\fR
737 with the time elapsed since the first GC event preceding each logged event\&. The
738 \fB\-Xloggc\fR
739 option overrides
740 \fB\-verbose:gc\fR
741 if both are given with the same
742 \fBjava\fR
743 command\&.
744 .sp
745 Example:
746 .sp
747 .if n \{\
748 .RS 4
749 .\}
750 .nf
751 \fB\-Xloggc:garbage\-collection\&.log\fR
752
753 .fi
754 .if n \{\
755 .RE
756 .\}
757 .RE
758 .PP
759 \-Xmaxjitcodesize=\fIsize\fR
760 .RS 4
761 Specifies the maximum code cache size (in bytes) for JIT\-compiled code\&. Append the letter
762 \fBk\fR
763 or
764 \fBK\fR
765 to indicate kilobytes,
766 \fBm\fR
767 or
768 \fBM\fR
769 to indicate megabytes,
770 \fBg\fR
771 or
772 \fBG\fR
773 to indicate gigabytes\&. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option
774 \fB\-XX:\-TieredCompilation\fR, then the default size is 48 MB:
775 .sp
776 .if n \{\
777 .RS 4
778 .\}
779 .nf
780 \fB\-Xmaxjitcodesize=240m\fR
781
782 .fi
783 .if n \{\
784 .RE
785 .\}
786 This option is equivalent to
787 \fB\-XX:ReservedCodeCacheSize\fR\&.
788 .RE
789 .PP
790 \-Xmixed
791 .RS 4
792 Executes all bytecode by the interpreter except for hot methods, which are compiled to native code\&.
793 .RE
794 .PP
795 \-Xmn\fIsize\fR
796 .RS 4
797 Sets the initial and maximum size (in bytes) of the heap for the young generation (nursery)\&. Append the letter
798 \fBk\fR
799 or
800 \fBK\fR
801 to indicate kilobytes,
802 \fBm\fR
803 or
804 \fBM\fR
805 to indicate megabytes,
806 \fBg\fR
807 or
808 \fBG\fR
809 to indicate gigabytes\&.
810 .sp
811 The young generation region of the heap is used for new objects\&. GC is performed in this region more often than in other regions\&. If the size for the young generation is too small, then a lot of minor garbage collections will be performed\&. If the size is too large, then only full garbage collections will be performed, which can take a long time to complete\&. Oracle recommends that you keep the size for the young generation between a half and a quarter of the overall heap size\&.
812 .sp
813 The following examples show how to set the initial and maximum size of young generation to 256 MB using various units:
814 .sp
815 .if n \{\
816 .RS 4
817 .\}
818 .nf
819 \fB\-Xmn256m\fR
820 \fB\-Xmn262144k\fR
821 \fB\-Xmn268435456\fR
822
823 .fi
824 .if n \{\
825 .RE
826 .\}
827 Instead of the
828 \fB\-Xmn\fR
829 option to set both the initial and maximum size of the heap for the young generation, you can use
830 \fB\-XX:NewSize\fR
831 to set the initial size and
832 \fB\-XX:MaxNewSize\fR
833 to set the maximum size\&.
834 .RE
835 .PP
836 \-Xms\fIsize\fR
837 .RS 4
838 Sets the initial size (in bytes) of the heap\&. This value must be a multiple of 1024 and greater than 1 MB\&. Append the letter
839 \fBk\fR
840 or
841 \fBK\fR
842 to indicate kilobytes,
843 \fBm\fR
844 or
845 \fBM\fR
846 to indicate megabytes,
847 \fBg\fR
848 or
849 \fBG\fR
850 to indicate gigabytes\&.
851 .sp
852 The following examples show how to set the size of allocated memory to 6 MB using various units:
853 .sp
854 .if n \{\
855 .RS 4
856 .\}
857 .nf
858 \fB\-Xms6291456\fR
859 \fB\-Xms6144k\fR
860 \fB\-Xms6m\fR
861
862 .fi
863 .if n \{\
864 .RE
865 .\}
866 If you do not set this option, then the initial size will be set as the sum of the sizes allocated for the old generation and the young generation\&. The initial size of the heap for the young generation can be set using the
867 \fB\-Xmn\fR
868 option or the
869 \fB\-XX:NewSize\fR
870 option\&.
871 .RE
872 .PP
873 \-Xmx\fIsize\fR
874 .RS 4
875 Specifies the maximum size (in bytes) of the memory allocation pool in bytes\&. This value must be a multiple of 1024 and greater than 2 MB\&. Append the letter
876 \fBk\fR
877 or
878 \fBK\fR
879 to indicate kilobytes,
880 \fBm\fR
881 or
882 \fBM\fR
883 to indicate megabytes,
884 \fBg\fR
885 or
886 \fBG\fR
887 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. For server deployments,
888 \fB\-Xms\fR
889 and
890 \fB\-Xmx\fR
891 are often set to the same value\&. See the section "Ergonomics" in
892 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
893 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
894 .sp
895 The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:
896 .sp
897 .if n \{\
898 .RS 4
899 .\}
900 .nf
901 \fB\-Xmx83886080\fR
902 \fB\-Xmx81920k\fR
903 \fB\-Xmx80m\fR
904
905 .fi
906 .if n \{\
907 .RE
908 .\}
909 The
910 \fB\-Xmx\fR
911 option is equivalent to
912 \fB\-XX:MaxHeapSize\fR\&.
913 .RE
914 .PP
915 \-Xnoclassgc
916 .RS 4
917 Disables garbage collection (GC) of classes\&. This can save some GC time, which shortens interruptions during the application run\&.
918 .sp
919 When you specify
920 \fB\-Xnoclassgc\fR
921 at startup, the class objects in the application will be left untouched during GC and will always be considered live\&. This can result in more memory being permanently occupied which, if not used carefully, will throw an out of memory exception\&.
922 .RE
923 .PP
924 \-Xprof
925 .RS 4
926 Profiles the running program and sends profiling data to standard output\&. This option is provided as a utility that is useful in program development and is not intended to be used in production systems\&.
927 .RE
928 .PP
929 \-Xrs
930 .RS 4
931 Reduces the use of operating system signals by the JVM\&.
932 .sp
933 Shutdown hooks enable orderly shutdown of a Java application by running user cleanup code (such as closing database connections) at shutdown, even if the JVM terminates abruptly\&.
934 .sp
935 The JVM catches signals to implement shutdown hooks for unexpected termination\&. The JVM uses
936 \fBSIGHUP\fR,
937 \fBSIGINT\fR, and
938 \fBSIGTERM\fR
939 to initiate the running of shutdown hooks\&.
940 .sp
941 The JVM uses a similar mechanism to implement the feature of dumping thread stacks for debugging purposes\&. The JVM uses
942 \fBSIGQUIT\fR
943 to perform thread dumps\&.
944 .sp
945 Applications embedding the JVM frequently need to trap signals such as
946 \fBSIGINT\fR
947 or
948 \fBSIGTERM\fR, which can lead to interference with the JVM signal handlers\&. The
949 \fB\-Xrs\fR
950 option is available to address this issue\&. When
951 \fB\-Xrs\fR
952 is used, the signal masks for
953 \fBSIGINT\fR,
954 \fBSIGTERM\fR,
955 \fBSIGHUP\fR, and
956 \fBSIGQUIT\fR
957 are not changed by the JVM, and signal handlers for these signals are not installed\&.
958 .sp
959 There are two consequences of specifying
960 \fB\-Xrs\fR:
961 .sp
962 .RS 4
963 .ie n \{\
964 \h'-04'\(bu\h'+03'\c
965 .\}
966 .el \{\
967 .sp -1
968 .IP \(bu 2.3
969 .\}
970 \fBSIGQUIT\fR
971 thread dumps are not available\&.
972 .RE
973 .sp
974 .RS 4
975 .ie n \{\
976 \h'-04'\(bu\h'+03'\c
977 .\}
978 .el \{\
979 .sp -1
980 .IP \(bu 2.3
981 .\}
982 User code is responsible for causing shutdown hooks to run, for example, by calling
983 \fBSystem\&.exit()\fR
984 when the JVM is to be terminated\&.
985 .RE
986 .RE
987 .PP
988 \-Xshare:\fImode\fR
989 .RS 4
990 Sets the class data sharing (CDS) mode\&. Possible
991 \fImode\fR
992 arguments for this option include the following:
993 .PP
994 auto
995 .RS 4
996 Use CDS if possible\&. This is the default value for Java HotSpot 32\-Bit Client VM\&.
997 .RE
998 .PP
999 on
1000 .RS 4
1001 Require the use of CDS\&. Print an error message and exit if class data sharing cannot be used\&.
1002 .RE
1003 .PP
1004 off
1005 .RS 4
1006 Do not use CDS\&. This is the default value for Java HotSpot 32\-Bit Server VM, Java HotSpot 64\-Bit Client VM, and Java HotSpot 64\-Bit Server VM\&.
1007 .RE
1008 .PP
1009 dump
1010 .RS 4
1011 Manually generate the CDS archive\&. Specify the application class path as described in "Setting the Class Path "\&.
1012 .sp
1013 You should regenerate the CDS archive with each new JDK release\&.
1014 .RE
1015 .RE
1016 .PP
1017 \-XshowSettings:\fIcategory\fR
1018 .RS 4
1019 Shows settings and continues\&. Possible
1020 \fIcategory\fR
1021 arguments for this option include the following:
1022 .PP
1023 all
1024 .RS 4
1025 Shows all categories of settings\&. This is the default value\&.
1026 .RE
1027 .PP
1028 locale
1029 .RS 4
1030 Shows settings related to locale\&.
1031 .RE
1032 .PP
1033 properties
1034 .RS 4
1035 Shows settings related to system properties\&.
1036 .RE
1037 .PP
1038 vm
1039 .RS 4
1040 Shows the settings of the JVM\&.
1041 .RE
1042 .RE
1043 .PP
1044 \-Xss\fIsize\fR
1045 .RS 4
1046 Sets the thread stack size (in bytes)\&. Append the letter
1047 \fBk\fR
1048 or
1049 \fBK\fR
1050 to indicate KB,
1051 \fBm\fR
1052 or
1053 \fBM\fR
1054 to indicate MB,
1055 \fBg\fR
1056 or
1057 \fBG\fR
1058 to indicate GB\&. The default value depends on the platform:
1059 .sp
1060 .RS 4
1061 .ie n \{\
1062 \h'-04'\(bu\h'+03'\c
1063 .\}
1064 .el \{\
1065 .sp -1
1066 .IP \(bu 2.3
1067 .\}
1068 Linux/ARM (32\-bit): 320 KB
1069 .RE
1070 .sp
1071 .RS 4
1072 .ie n \{\
1073 \h'-04'\(bu\h'+03'\c
1074 .\}
1075 .el \{\
1076 .sp -1
1077 .IP \(bu 2.3
1078 .\}
1079 Linux/i386 (32\-bit): 320 KB
1080 .RE
1081 .sp
1082 .RS 4
1083 .ie n \{\
1084 \h'-04'\(bu\h'+03'\c
1085 .\}
1086 .el \{\
1087 .sp -1
1088 .IP \(bu 2.3
1089 .\}
1090 Linux/x64 (64\-bit): 1024 KB
1091 .RE
1092 .sp
1093 .RS 4
1094 .ie n \{\
1095 \h'-04'\(bu\h'+03'\c
1096 .\}
1097 .el \{\
1098 .sp -1
1099 .IP \(bu 2.3
1100 .\}
1101 OS X (64\-bit): 1024 KB
1102 .RE
1103 .sp
1104 .RS 4
1105 .ie n \{\
1106 \h'-04'\(bu\h'+03'\c
1107 .\}
1108 .el \{\
1109 .sp -1
1110 .IP \(bu 2.3
1111 .\}
1112 Oracle Solaris/i386 (32\-bit): 320 KB
1113 .RE
1114 .sp
1115 .RS 4
1116 .ie n \{\
1117 \h'-04'\(bu\h'+03'\c
1118 .\}
1119 .el \{\
1120 .sp -1
1121 .IP \(bu 2.3
1122 .\}
1123 Oracle Solaris/x64 (64\-bit): 1024 KB
1124 .RE
1125 .sp
1126 The following examples set the thread stack size to 1024 KB in different units:
1127 .sp
1128 .if n \{\
1129 .RS 4
1130 .\}
1131 .nf
1132 \fB\-Xss1m\fR
1133 \fB\-Xss1024k\fR
1134 \fB\-Xss1048576\fR
1135
1136 .fi
1137 .if n \{\
1138 .RE
1139 .\}
1140 This option is equivalent to
1141 \fB\-XX:ThreadStackSize\fR\&.
1142 .RE
1143 .PP
1144 \-Xusealtsigs
1145 .RS 4
1146 Use alternative signals instead of
1147 \fBSIGUSR1\fR
1148 and
1149 \fBSIGUSR2\fR
1150 for JVM internal signals\&. This option is equivalent to
1151 \fB\-XX:+UseAltSigs\fR\&.
1152 .RE
1153 .PP
1154 \-Xverify:\fImode\fR
1155 .RS 4
1156 Sets the mode of the bytecode verifier\&. Bytecode verification helps to troubleshoot some problems, but it also adds overhead to the running application\&. Possible
1157 \fImode\fR
1158 arguments for this option include the following:
1159 .PP
1160 none
1161 .RS 4
1162 Do not verify the bytecode\&. This reduces startup time and also reduces the protection provided by Java\&.
1163 .RE
1164 .PP
1165 remote
1166 .RS 4
1167 Verify those classes that are not loaded by the bootstrap class loader\&. This is the default behavior if you do not specify the
1168 \fB\-Xverify\fR
1169 option\&.
1170 .RE
1171 .PP
1172 all
1173 .RS 4
1174 Verify all classes\&.
1175 .RE
1176 .RE
1177 .SS "Advanced Runtime Options"
1178 .PP
1179 These options control the runtime behavior of the Java HotSpot VM\&.
1180 .PP
1181 \-XX:+CheckEndorsedAndExtDirs
1182 .RS 4
1183 Enables the option to prevent the
1184 \fBjava\fR
1185 command from running a Java application if it uses the endorsed\-standards override mechanism or the extension mechanism\&. This option checks if an application is using one of these mechanisms by checking the following:
1186 .sp
1187 .RS 4
1188 .ie n \{\
1189 \h'-04'\(bu\h'+03'\c
1190 .\}
1191 .el \{\
1192 .sp -1
1193 .IP \(bu 2.3
1194 .\}
1195 The
1196 \fBjava\&.ext\&.dirs\fR
1197 or
1198 \fBjava\&.endorsed\&.dirs\fR
1199 system property is set\&.
1200 .RE
1201 .sp
1202 .RS 4
1203 .ie n \{\
1204 \h'-04'\(bu\h'+03'\c
1205 .\}
1206 .el \{\
1207 .sp -1
1208 .IP \(bu 2.3
1209 .\}
1210 The
1211 \fBlib/endorsed\fR
1212 directory exists and is not empty\&.
1213 .RE
1214 .sp
1215 .RS 4
1216 .ie n \{\
1217 \h'-04'\(bu\h'+03'\c
1218 .\}
1219 .el \{\
1220 .sp -1
1221 .IP \(bu 2.3
1222 .\}
1223 The
1224 \fBlib/ext\fR
1225 directory contains any JAR files other than those of the JDK\&.
1226 .RE
1227 .sp
1228 .RS 4
1229 .ie n \{\
1230 \h'-04'\(bu\h'+03'\c
1231 .\}
1232 .el \{\
1233 .sp -1
1234 .IP \(bu 2.3
1235 .\}
1236 The system\-wide platform\-specific extension directory contains any JAR files\&.
1237 .RE
1238 .RE
1239 .PP
1240 \-XX:+DisableAttachMechanism
1241 .RS 4
1242 Enables the option that disables the mechanism that lets tools attach to the JVM\&. By default, this option is disabled, meaning that the attach mechanism is enabled and you can use tools such as
1243 \fBjcmd\fR,
1244 \fBjstack\fR,
1245 \fBjmap\fR, and
1246 \fBjinfo\fR\&.
1247 .RE
1248 .PP
1249 \-XX:ErrorFile=\fIfilename\fR
1250 .RS 4
1251 Specifies the path and file name to which error data is written when an irrecoverable error occurs\&. By default, this file is created in the current working directory and named
1252 \fBhs_err_pid\fR\fIpid\fR\fB\&.log\fR
1253 where
1254 \fIpid\fR
1255 is the identifier of the process that caused the error\&. The following example shows how to set the default log file (note that the identifier of the process is specified as
1256 \fB%p\fR):
1257 .sp
1258 .if n \{\
1259 .RS 4
1260 .\}
1261 .nf
1262 \fB\-XX:ErrorFile=\&./hs_err_pid%p\&.log\fR
1263
1264 .fi
1265 .if n \{\
1266 .RE
1267 .\}
1268 The following example shows how to set the error log to
1269 \fB/var/log/java/java_error\&.log\fR:
1270 .sp
1271 .if n \{\
1272 .RS 4
1273 .\}
1274 .nf
1275 \fB\-XX:ErrorFile=/var/log/java/java_error\&.log\fR
1276
1277 .fi
1278 .if n \{\
1279 .RE
1280 .\}
1281 If the file cannot be created in the specified directory (due to insufficient space, permission problem, or another issue), then the file is created in the temporary directory for the operating system\&. The temporary directory is
1282 \fB/tmp\fR\&.
1283 .RE
1284 .PP
1285 \-XX:+FailOverToOldVerifier
1286 .RS 4
1287 Enables automatic failover to the old verifier when the new type checker fails\&. By default, this option is disabled and it is ignored (that is, treated as disabled) for classes with a recent bytecode version\&. You can enable it for classes with older versions of the bytecode\&.
1288 .RE
1289 .PP
1290 \-XX:LargePageSizeInBytes=\fIsize\fR
1291 .RS 4
1292 On Solaris, sets the maximum size (in bytes) for large pages used for Java heap\&. The
1293 \fIsize\fR
1294 argument must be a power of 2 (2, 4, 8, 16, \&.\&.\&.)\&. Append the letter
1295 \fBk\fR
1296 or
1297 \fBK\fR
1298 to indicate kilobytes,
1299 \fBm\fR
1300 or
1301 \fBM\fR
1302 to indicate megabytes,
1303 \fBg\fR
1304 or
1305 \fBG\fR
1306 to indicate gigabytes\&. By default, the size is set to 0, meaning that the JVM chooses the size for large pages automatically\&.
1307 .sp
1308 The following example illustrates how to set the large page size to 4 megabytes (MB):
1309 .sp
1310 .if n \{\
1311 .RS 4
1312 .\}
1313 .nf
1314 \fB\-XX:LargePageSizeInBytes=4m\fR
1315
1316 .fi
1317 .if n \{\
1318 .RE
1319 .\}
1320 .RE
1321 .PP
1322 \-XX:MaxDirectMemorySize=\fIsize\fR
1323 .RS 4
1324 Sets the maximum total size (in bytes) of the New I/O (the
1325 \fBjava\&.nio\fR
1326 package) direct\-buffer allocations\&. Append the letter
1327 \fBk\fR
1328 or
1329 \fBK\fR
1330 to indicate kilobytes,
1331 \fBm\fR
1332 or
1333 \fBM\fR
1334 to indicate megabytes,
1335 \fBg\fR
1336 or
1337 \fBG\fR
1338 to indicate gigabytes\&. By default, the size is set to 0, meaning that the JVM chooses the size for NIO direct\-buffer allocations automatically\&.
1339 .sp
1340 The following examples illustrate how to set the NIO size to 1024 KB in different units:
1341 .sp
1342 .if n \{\
1343 .RS 4
1344 .\}
1345 .nf
1346 \fB\-XX:MaxDirectMemorySize=1m\fR
1347 \fB\-XX:MaxDirectMemorySize=1024k\fR
1348 \fB\-XX:MaxDirectMemorySize=1048576\fR
1349
1350 .fi
1351 .if n \{\
1352 .RE
1353 .\}
1354 .RE
1355 .PP
1356 \-XX:NativeMemoryTracking=\fImode\fR
1357 .RS 4
1358 Specifies the mode for tracking JVM native memory usage\&. Possible
1359 \fImode\fR
1360 arguments for this option include the following:
1361 .PP
1362 off
1363 .RS 4
1364 Do not track JVM native memory usage\&. This is the default behavior if you do not specify the
1365 \fB\-XX:NativeMemoryTracking\fR
1366 option\&.
1367 .RE
1368 .PP
1369 summary
1370 .RS 4
1371 Only track memory usage by JVM subsystems, such as Java heap, class, code, and thread\&.
1372 .RE
1373 .PP
1374 detail
1375 .RS 4
1376 In addition to tracking memory usage by JVM subsystems, track memory usage by individual
1377 \fBCallSite\fR, individual virtual memory region and its committed regions\&.
1378 .RE
1379 .RE
1380 .PP
1381 \-XX:ObjectAlignmentInBytes=\fIalignment\fR
1382 .RS 4
1383 Sets the memory alignment of Java objects (in bytes)\&. By default, the value is set to 8 bytes\&. The specified value should be a power of two, and must be within the range of 8 and 256 (inclusive)\&. This option makes it possible to use compressed pointers with large Java heap sizes\&.
1384 .sp
1385 The heap size limit in bytes is calculated as:
1386 .sp
1387 \fB4GB * ObjectAlignmentInBytes\fR
1388 .sp
1389 Note: As the alignment value increases, the unused space between objects will also increase\&. As a result, you may not realize any benefits from using compressed pointers with large Java heap sizes\&.
1390 .RE
1391 .PP
1392 \-XX:OnError=\fIstring\fR
1393 .RS 4
1394 Sets a custom command or a series of semicolon\-separated commands to run when an irrecoverable error occurs\&. If the string contains spaces, then it must be enclosed in quotation marks\&.
1395 .sp
1396 The following example shows how the
1397 \fB\-XX:OnError\fR
1398 option can be used to run the
1399 \fBgcore\fR
1400 command to create the core image, and the debugger is started to attach to the process in case of an irrecoverable error (the
1401 \fB%p\fR
1402 designates the current process):
1403 .sp
1404 .if n \{\
1405 .RS 4
1406 .\}
1407 .nf
1408 \fB\-XX:OnError="gcore %p;dbx \- %p"\fR
1409
1410 .fi
1411 .if n \{\
1412 .RE
1413 .\}
1414 .RE
1415 .PP
1416 \-XX:OnOutOfMemoryError=\fIstring\fR
1417 .RS 4
1418 Sets a custom command or a series of semicolon\-separated commands to run when an
1419 \fBOutOfMemoryError\fR
1420 exception is first thrown\&. If the string contains spaces, then it must be enclosed in quotation marks\&. For an example of a command string, see the description of the
1421 \fB\-XX:OnError\fR
1422 option\&.
1423 .RE
1424 .PP
1425 \-XX:+PerfDataSaveToFile
1426 .RS 4
1427 If enabled, saves
1428 jstat(1) binary data when the Java application exits\&. This binary data is saved in a file named
1429 \fBhsperfdata_\fR\fI<pid>\fR, where
1430 \fI<pid>\fR
1431 is the process identifier of the Java application you ran\&. Use
1432 \fBjstat\fR
1433 to display the performance data contained in this file as follows:
1434 .sp
1435 .if n \{\
1436 .RS 4
1437 .\}
1438 .nf
1439 \fBjstat \-class file:///\fR\fB\fI<path>\fR\fR\fB/hsperfdata_\fR\fB\fI<pid>\fR\fR
1440 \fBjstat \-gc file:///\fR\fB\fI<path>\fR\fR\fB/hsperfdata_\fR\fB\fI<pid>\fR\fR
1441 .fi
1442 .if n \{\
1443 .RE
1444 .\}
1445 .RE
1446 .PP
1447 \-XX:+PrintCommandLineFlags
1448 .RS 4
1449 Enables printing of ergonomically selected JVM flags that appeared on the command line\&. It can be useful to know the ergonomic values set by the JVM, such as the heap space size and the selected garbage collector\&. By default, this option is disabled and flags are not printed\&.
1450 .RE
1451 .PP
1452 \-XX:+PrintNMTStatistics
1453 .RS 4
1454 Enables printing of collected native memory tracking data at JVM exit when native memory tracking is enabled (see
1455 \fB\-XX:NativeMemoryTracking\fR)\&. By default, this option is disabled and native memory tracking data is not printed\&.
1456 .RE
1457 .PP
1458 \-XX:+RelaxAccessControlCheck
1459 .RS 4
1460 Decreases the amount of access control checks in the verifier\&. By default, this option is disabled, and it is ignored (that is, treated as disabled) for classes with a recent bytecode version\&. You can enable it for classes with older versions of the bytecode\&.
1461 .RE
1462 .PP
1463 \-XX:+ShowMessageBoxOnError
1464 .RS 4
1465 Enables displaying of a dialog box when the JVM experiences an irrecoverable error\&. This prevents the JVM from exiting and keeps the process active so that you can attach a debugger to it to investigate the cause of the error\&. By default, this option is disabled\&.
1466 .RE
1467 .PP
1468 \-XX:ThreadStackSize=\fIsize\fR
1469 .RS 4
1470 Sets the thread stack size (in bytes)\&. Append the letter
1471 \fBk\fR
1472 or
1473 \fBK\fR
1474 to indicate kilobytes,
1475 \fBm\fR
1476 or
1477 \fBM\fR
1478 to indicate megabytes,
1479 \fBg\fR
1480 or
1481 \fBG\fR
1482 to indicate gigabytes\&. The default value depends on the platform:
1483 .sp
1484 .RS 4
1485 .ie n \{\
1486 \h'-04'\(bu\h'+03'\c
1487 .\}
1488 .el \{\
1489 .sp -1
1490 .IP \(bu 2.3
1491 .\}
1492 Linux/ARM (32\-bit): 320 KB
1493 .RE
1494 .sp
1495 .RS 4
1496 .ie n \{\
1497 \h'-04'\(bu\h'+03'\c
1498 .\}
1499 .el \{\
1500 .sp -1
1501 .IP \(bu 2.3
1502 .\}
1503 Linux/i386 (32\-bit): 320 KB
1504 .RE
1505 .sp
1506 .RS 4
1507 .ie n \{\
1508 \h'-04'\(bu\h'+03'\c
1509 .\}
1510 .el \{\
1511 .sp -1
1512 .IP \(bu 2.3
1513 .\}
1514 Linux/x64 (64\-bit): 1024 KB
1515 .RE
1516 .sp
1517 .RS 4
1518 .ie n \{\
1519 \h'-04'\(bu\h'+03'\c
1520 .\}
1521 .el \{\
1522 .sp -1
1523 .IP \(bu 2.3
1524 .\}
1525 OS X (64\-bit): 1024 KB
1526 .RE
1527 .sp
1528 .RS 4
1529 .ie n \{\
1530 \h'-04'\(bu\h'+03'\c
1531 .\}
1532 .el \{\
1533 .sp -1
1534 .IP \(bu 2.3
1535 .\}
1536 Oracle Solaris/i386 (32\-bit): 320 KB
1537 .RE
1538 .sp
1539 .RS 4
1540 .ie n \{\
1541 \h'-04'\(bu\h'+03'\c
1542 .\}
1543 .el \{\
1544 .sp -1
1545 .IP \(bu 2.3
1546 .\}
1547 Oracle Solaris/x64 (64\-bit): 1024 KB
1548 .RE
1549 .sp
1550 The following examples show how to set the thread stack size to 1024 KB in different units:
1551 .sp
1552 .if n \{\
1553 .RS 4
1554 .\}
1555 .nf
1556 \fB\-XX:ThreadStackSize=1m\fR
1557 \fB\-XX:ThreadStackSize=1024k\fR
1558 \fB\-XX:ThreadStackSize=1048576\fR
1559
1560 .fi
1561 .if n \{\
1562 .RE
1563 .\}
1564 This option is equivalent to
1565 \fB\-Xss\fR\&.
1566 .RE
1567 .PP
1568 \-XX:+TraceClassLoading
1569 .RS 4
1570 Enables tracing of classes as they are loaded\&. By default, this option is disabled and classes are not traced\&.
1571 .RE
1572 .PP
1573 \-XX:+TraceClassLoadingPreorder
1574 .RS 4
1575 Enables tracing of all loaded classes in the order in which they are referenced\&. By default, this option is disabled and classes are not traced\&.
1576 .RE
1577 .PP
1578 \-XX:+TraceClassResolution
1579 .RS 4
1580 Enables tracing of constant pool resolutions\&. By default, this option is disabled and constant pool resolutions are not traced\&.
1581 .RE
1582 .PP
1583 \-XX:+TraceClassUnloading
1584 .RS 4
1585 Enables tracing of classes as they are unloaded\&. By default, this option is disabled and classes are not traced\&.
1586 .RE
1587 .PP
1588 \-XX:+TraceLoaderConstraints
1589 .RS 4
1590 Enables tracing of the loader constraints recording\&. By default, this option is disabled and loader constraints recording is not traced\&.
1591 .RE
1592 .PP
1593 \-XX:+UseAltSigs
1594 .RS 4
1595 Enables the use of alternative signals instead of
1596 \fBSIGUSR1\fR
1597 and
1598 \fBSIGUSR2\fR
1599 for JVM internal signals\&. By default, this option is disabled and alternative signals are not used\&. This option is equivalent to
1600 \fB\-Xusealtsigs\fR\&.
1601 .RE
1602 .PP
1603 \-XX:\-UseBiasedLocking
1604 .RS 4
1605 Disables the use of biased locking\&. Some applications with significant amounts of uncontended synchronization may attain significant speedups with this flag enabled, whereas applications with certain patterns of locking may see slowdowns\&. For more information about the biased locking technique, see the example in Java Tuning White Paper at http://www\&.oracle\&.com/technetwork/java/tuning\-139912\&.html#section4\&.2\&.5
1606 .sp
1607 By default, this option is enabled\&.
1608 .RE
1609 .PP
1610 \-XX:\-UseCompressedOops
1611 .RS 4
1612 Disables the use of compressed pointers\&. By default, this option is enabled, and compressed pointers are used when Java heap sizes are less than 32 GB\&. When this option is enabled, object references are represented as 32\-bit offsets instead of 64\-bit pointers, which typically increases performance when running the application with Java heap sizes less than 32 GB\&. This option works only for 64\-bit JVMs\&.
1613 .sp
1614 It is also possible to use compressed pointers when Java heap sizes are greater than 32GB\&. See the
1615 \fB\-XX:ObjectAlignmentInBytes\fR
1616 option\&.
1617 .RE
1618 .PP
1619 \-XX:+UseHugeTLBFS
1620 .RS 4
1621 This option for Linux is the equivalent of specifying
1622 \fB\-XX:+UseLargePages\fR\&. This option is disabled by default\&. This option pre\-allocates all large pages up\-front, when memory is reserved; consequently the JVM cannot dynamically grow or shrink large pages memory areas; see
1623 \fB\-XX:UseTransparentHugePages\fR
1624 if you want this behavior\&.
1625 .sp
1626 For more information, see "Large Pages"\&.
1627 .RE
1628 .PP
1629 \-XX:+UseLargePages
1630 .RS 4
1631 Enables the use of large page memory\&. By default, this option is disabled and large page memory is not used\&.
1632 .sp
1633 For more information, see "Large Pages"\&.
1634 .RE
1635 .PP
1636 \-XX:+UseMembar
1637 .RS 4
1638 Enables issuing of membars on thread state transitions\&. This option is disabled by default on all platforms except ARM servers, where it is enabled\&. (It is recommended that you do not disable this option on ARM servers\&.)
1639 .RE
1640 .PP
1641 \-XX:+UsePerfData
1642 .RS 4
1643 Enables the
1644 \fBperfdata\fR
1645 feature\&. This option is enabled by default to allow JVM monitoring and performance testing\&. Disabling it suppresses the creation of the
1646 \fBhsperfdata_userid\fR
1647 directories\&. To disable the
1648 \fBperfdata\fR
1649 feature, specify
1650 \fB\-XX:\-UsePerfData\fR\&.
1651 .RE
1652 .PP
1653 \-XX:+UseTransparentHugePages
1654 .RS 4
1655 On Linux, enables the use of large pages that can dynamically grow or shrink\&. This option is disabled by default\&. You may encounter performance problems with transparent huge pages as the OS moves other pages around to create huge pages; this option is made available for experimentation\&.
1656 .sp
1657 For more information, see "Large Pages"\&.
1658 .RE
1659 .PP
1660 \-XX:+AllowUserSignalHandlers
1661 .RS 4
1662 Enables installation of signal handlers by the application\&. By default, this option is disabled and the application is not allowed to install signal handlers\&.
1663 .RE
1664 .SS "Advanced JIT Compiler Options"
1665 .PP
1666 These options control the dynamic just\-in\-time (JIT) compilation performed by the Java HotSpot VM\&.
1667 .PP
1668 \-XX:+AggressiveOpts
1669 .RS 4
1670 Enables the use of aggressive performance optimization features, which are expected to become default in upcoming releases\&. By default, this option is disabled and experimental performance features are not used\&.
1671 .RE
1672 .PP
1673 \-XX:AllocateInstancePrefetchLines=\fIlines\fR
1674 .RS 4
1675 Sets the number of lines to prefetch ahead of the instance allocation pointer\&. By default, the number of lines to prefetch is set to 1:
1676 .sp
1677 .if n \{\
1678 .RS 4
1679 .\}
1680 .nf
1681 \fB\-XX:AllocateInstancePrefetchLines=1\fR
1682
1683 .fi
1684 .if n \{\
1685 .RE
1686 .\}
1687 Only the Java HotSpot Server VM supports this option\&.
1688 .RE
1689 .PP
1690 \-XX:AllocatePrefetchDistance=\fIsize\fR
1691 .RS 4
1692 Sets the size (in bytes) of the prefetch distance for object allocation\&. Memory about to be written with the value of new objects is prefetched up to this distance starting from the address of the last allocated object\&. Each Java thread has its own allocation point\&.
1693 .sp
1694 Negative values denote that prefetch distance is chosen based on the platform\&. Positive values are bytes to prefetch\&. Append the letter
1695 \fBk\fR
1696 or
1697 \fBK\fR
1698 to indicate kilobytes,
1699 \fBm\fR
1700 or
1701 \fBM\fR
1702 to indicate megabytes,
1703 \fBg\fR
1704 or
1705 \fBG\fR
1706 to indicate gigabytes\&. The default value is set to \-1\&.
1707 .sp
1708 The following example shows how to set the prefetch distance to 1024 bytes:
1709 .sp
1710 .if n \{\
1711 .RS 4
1712 .\}
1713 .nf
1714 \fB\-XX:AllocatePrefetchDistance=1024\fR
1715
1716 .fi
1717 .if n \{\
1718 .RE
1719 .\}
1720 Only the Java HotSpot Server VM supports this option\&.
1721 .RE
1722 .PP
1723 \-XX:AllocatePrefetchInstr=\fIinstruction\fR
1724 .RS 4
1725 Sets the prefetch instruction to prefetch ahead of the allocation pointer\&. Only the Java HotSpot Server VM supports this option\&. Possible values are from 0 to 3\&. The actual instructions behind the values depend on the platform\&. By default, the prefetch instruction is set to 0:
1726 .sp
1727 .if n \{\
1728 .RS 4
1729 .\}
1730 .nf
1731 \fB\-XX:AllocatePrefetchInstr=0\fR
1732
1733 .fi
1734 .if n \{\
1735 .RE
1736 .\}
1737 Only the Java HotSpot Server VM supports this option\&.
1738 .RE
1739 .PP
1740 \-XX:AllocatePrefetchLines=\fIlines\fR
1741 .RS 4
1742 Sets the number of cache lines to load after the last object allocation by using the prefetch instructions generated in compiled code\&. The default value is 1 if the last allocated object was an instance, and 3 if it was an array\&.
1743 .sp
1744 The following example shows how to set the number of loaded cache lines to 5:
1745 .sp
1746 .if n \{\
1747 .RS 4
1748 .\}
1749 .nf
1750 \fB\-XX:AllocatePrefetchLines=5\fR
1751
1752 .fi
1753 .if n \{\
1754 .RE
1755 .\}
1756 Only the Java HotSpot Server VM supports this option\&.
1757 .RE
1758 .PP
1759 \-XX:AllocatePrefetchStepSize=\fIsize\fR
1760 .RS 4
1761 Sets the step size (in bytes) for sequential prefetch instructions\&. Append the letter
1762 \fBk\fR
1763 or
1764 \fBK\fR
1765 to indicate kilobytes,
1766 \fBm\fR
1767 or
1768 \fBM\fR
1769 to indicate megabytes,
1770 \fBg\fR
1771 or
1772 \fBG\fR
1773 to indicate gigabytes\&. By default, the step size is set to 16 bytes:
1774 .sp
1775 .if n \{\
1776 .RS 4
1777 .\}
1778 .nf
1779 \fB\-XX:AllocatePrefetchStepSize=16\fR
1780
1781 .fi
1782 .if n \{\
1783 .RE
1784 .\}
1785 Only the Java HotSpot Server VM supports this option\&.
1786 .RE
1787 .PP
1788 \-XX:AllocatePrefetchStyle=\fIstyle\fR
1789 .RS 4
1790 Sets the generated code style for prefetch instructions\&. The
1791 \fIstyle\fR
1792 argument is an integer from 0 to 3:
1793 .PP
1794 0
1795 .RS 4
1796 Do not generate prefetch instructions\&.
1797 .RE
1798 .PP
1799 1
1800 .RS 4
1801 Execute prefetch instructions after each allocation\&. This is the default parameter\&.
1802 .RE
1803 .PP
1804 2
1805 .RS 4
1806 Use the thread\-local allocation block (TLAB) watermark pointer to determine when prefetch instructions are executed\&.
1807 .RE
1808 .PP
1809 3
1810 .RS 4
1811 Use BIS instruction on SPARC for allocation prefetch\&.
1812 .RE
1813 .sp
1814 Only the Java HotSpot Server VM supports this option\&.
1815 .RE
1816 .PP
1817 \-XX:+BackgroundCompilation
1818 .RS 4
1819 Enables background compilation\&. This option is enabled by default\&. To disable background compilation, specify
1820 \fB\-XX:\-BackgroundCompilation\fR
1821 (this is equivalent to specifying
1822 \fB\-Xbatch\fR)\&.
1823 .RE
1824 .PP
1825 \-XX:CICompilerCount=\fIthreads\fR
1826 .RS 4
1827 Sets the number of compiler threads to use for compilation\&. By default, the number of threads is set to 2 for the server JVM, to 1 for the client JVM, and it scales to the number of cores if tiered compilation is used\&. The following example shows how to set the number of threads to 2:
1828 .sp
1829 .if n \{\
1830 .RS 4
1831 .\}
1832 .nf
1833 \fB\-XX:CICompilerCount=2\fR
1834
1835 .fi
1836 .if n \{\
1837 .RE
1838 .\}
1839 .RE
1840 .PP
1841 \-XX:CodeCacheMinimumFreeSpace=\fIsize\fR
1842 .RS 4
1843 Sets the minimum free space (in bytes) required for compilation\&. Append the letter
1844 \fBk\fR
1845 or
1846 \fBK\fR
1847 to indicate kilobytes,
1848 \fBm\fR
1849 or
1850 \fBM\fR
1851 to indicate megabytes,
1852 \fBg\fR
1853 or
1854 \fBG\fR
1855 to indicate gigabytes\&. When less than the minimum free space remains, compiling stops\&. By default, this option is set to 500 KB\&. The following example shows how to set the minimum free space to 1024 MB:
1856 .sp
1857 .if n \{\
1858 .RS 4
1859 .\}
1860 .nf
1861 \fB\-XX:CodeCacheMinimumFreeSpace=1024m\fR
1862
1863 .fi
1864 .if n \{\
1865 .RE
1866 .\}
1867 .RE
1868 .PP
1869 \-XX:CompileCommand=\fIcommand\fR,\fImethod\fR[,\fIoption\fR]
1870 .RS 4
1871 Specifies a command to perform on a method\&. For example, to exclude the
1872 \fBindexOf()\fR
1873 method of the
1874 \fBString\fR
1875 class from being compiled, use the following:
1876 .sp
1877 .if n \{\
1878 .RS 4
1879 .\}
1880 .nf
1881 \fB\-XX:CompileCommand=exclude,java/lang/String\&.indexOf\fR
1882
1883 .fi
1884 .if n \{\
1885 .RE
1886 .\}
1887 Note that the full class name is specified, including all packages and subpackages separated by a slash (\fB/\fR)\&. For easier cut and paste operations, it is also possible to use the method name format produced by the
1888 \fB\-XX:+PrintCompilation\fR
1889 and
1890 \fB\-XX:+LogCompilation\fR
1891 options:
1892 .sp
1893 .if n \{\
1894 .RS 4
1895 .\}
1896 .nf
1897 \fB\-XX:CompileCommand=exclude,java\&.lang\&.String::indexOf\fR
1898
1899 .fi
1900 .if n \{\
1901 .RE
1902 .\}
1903 If the method is specified without the signature, the command will be applied to all methods with the specified name\&. However, you can also specify the signature of the method in the class file format\&. In this case, you should enclose the arguments in quotation marks, because otherwise the shell treats the semicolon as command end\&. For example, if you want to exclude only the
1904 \fBindexOf(String)\fR
1905 method of the
1906 \fBString\fR
1907 class from being compiled, use the following:
1908 .sp
1909 .if n \{\
1910 .RS 4
1911 .\}
1912 .nf
1913 \fB\-XX:CompileCommand="exclude,java/lang/String\&.indexOf,(Ljava/lang/String;)I"\fR
1914
1915 .fi
1916 .if n \{\
1917 .RE
1918 .\}
1919 You can also use the asterisk (*) as a wildcard for class and method names\&. For example, to exclude all
1920 \fBindexOf()\fR
1921 methods in all classes from being compiled, use the following:
1922 .sp
1923 .if n \{\
1924 .RS 4
1925 .\}
1926 .nf
1927 \fB\-XX:CompileCommand=exclude,*\&.indexOf\fR
1928
1929 .fi
1930 .if n \{\
1931 .RE
1932 .\}
1933 The commas and periods are aliases for spaces, making it easier to pass compiler commands through a shell\&. You can pass arguments to
1934 \fB\-XX:CompileCommand\fR
1935 using spaces as separators by enclosing the argument in quotation marks:
1936 .sp
1937 .if n \{\
1938 .RS 4
1939 .\}
1940 .nf
1941 \fB\-XX:CompileCommand="exclude java/lang/String indexOf"\fR
1942
1943 .fi
1944 .if n \{\
1945 .RE
1946 .\}
1947 Note that after parsing the commands passed on the command line using the
1948 \fB\-XX:CompileCommand\fR
1949 options, the JIT compiler then reads commands from the
1950 \fB\&.hotspot_compiler\fR
1951 file\&. You can add commands to this file or specify a different file using the
1952 \fB\-XX:CompileCommandFile\fR
1953 option\&.
1954 .sp
1955 To add several commands, either specify the
1956 \fB\-XX:CompileCommand\fR
1957 option multiple times, or separate each argument with the newline separator (\fB\en\fR)\&. The following commands are available:
1958 .PP
1959 break
1960 .RS 4
1961 Set a breakpoint when debugging the JVM to stop at the beginning of compilation of the specified method\&.
1962 .RE
1963 .PP
1964 compileonly
1965 .RS 4
1966 Exclude all methods from compilation except for the specified method\&. As an alternative, you can use the
1967 \fB\-XX:CompileOnly\fR
1968 option, which allows to specify several methods\&.
1969 .RE
1970 .PP
1971 dontinline
1972 .RS 4
1973 Prevent inlining of the specified method\&.
1974 .RE
1975 .PP
1976 exclude
1977 .RS 4
1978 Exclude the specified method from compilation\&.
1979 .RE
1980 .PP
1981 help
1982 .RS 4
1983 Print a help message for the
1984 \fB\-XX:CompileCommand\fR
1985 option\&.
1986 .RE
1987 .PP
1988 inline
1989 .RS 4
1990 Attempt to inline the specified method\&.
1991 .RE
1992 .PP
1993 log
1994 .RS 4
1995 Exclude compilation logging (with the
1996 \fB\-XX:+LogCompilation\fR
1997 option) for all methods except for the specified method\&. By default, logging is performed for all compiled methods\&.
1998 .RE
1999 .PP
2000 option
2001 .RS 4
2002 This command can be used to pass a JIT compilation option to the specified method in place of the last argument (\fIoption\fR)\&. The compilation option is set at the end, after the method name\&. For example, to enable the
2003 \fBBlockLayoutByFrequency\fR
2004 option for the
2005 \fBappend()\fR
2006 method of the
2007 \fBStringBuffer\fR
2008 class, use the following:
2009 .sp
2010 .if n \{\
2011 .RS 4
2012 .\}
2013 .nf
2014 \fB\-XX:CompileCommand=option,java/lang/StringBuffer\&.append,BlockLayoutByFrequency\fR
2015
2016 .fi
2017 .if n \{\
2018 .RE
2019 .\}
2020 You can specify multiple compilation options, separated by commas or spaces\&.
2021 .RE
2022 .PP
2023 print
2024 .RS 4
2025 Print generated assembler code after compilation of the specified method\&.
2026 .RE
2027 .PP
2028 quiet
2029 .RS 4
2030 Do not print the compile commands\&. By default, the commands that you specify with the \-\fBXX:CompileCommand\fR
2031 option are printed; for example, if you exclude from compilation the
2032 \fBindexOf()\fR
2033 method of the
2034 \fBString\fR
2035 class, then the following will be printed to standard output:
2036 .sp
2037 .if n \{\
2038 .RS 4
2039 .\}
2040 .nf
2041 \fBCompilerOracle: exclude java/lang/String\&.indexOf\fR
2042
2043 .fi
2044 .if n \{\
2045 .RE
2046 .\}
2047 You can suppress this by specifying the
2048 \fB\-XX:CompileCommand=quiet\fR
2049 option before other
2050 \fB\-XX:CompileCommand\fR
2051 options\&.
2052 .RE
2053 .RE
2054 .PP
2055 \-XX:CompileCommandFile=\fIfilename\fR
2056 .RS 4
2057 Sets the file from which JIT compiler commands are read\&. By default, the
2058 \fB\&.hotspot_compiler\fR
2059 file is used to store commands performed by the JIT compiler\&.
2060 .sp
2061 Each line in the command file represents a command, a class name, and a method name for which the command is used\&. For example, this line prints assembly code for the
2062 \fBtoString()\fR
2063 method of the
2064 \fBString\fR
2065 class:
2066 .sp
2067 .if n \{\
2068 .RS 4
2069 .\}
2070 .nf
2071 \fBprint java/lang/String toString\fR
2072
2073 .fi
2074 .if n \{\
2075 .RE
2076 .\}
2077 For more information about specifying the commands for the JIT compiler to perform on methods, see the
2078 \fB\-XX:CompileCommand\fR
2079 option\&.
2080 .RE
2081 .PP
2082 \-XX:CompileOnly=\fImethods\fR
2083 .RS 4
2084 Sets the list of methods (separated by commas) to which compilation should be restricted\&. Only the specified methods will be compiled\&. Specify each method with the full class name (including the packages and subpackages)\&. For example, to compile only the
2085 \fBlength()\fR
2086 method of the
2087 \fBString\fR
2088 class and the
2089 \fBsize()\fR
2090 method of the
2091 \fBList\fR
2092 class, use the following:
2093 .sp
2094 .if n \{\
2095 .RS 4
2096 .\}
2097 .nf
2098 \fB\-XX:CompileOnly=java/lang/String\&.length,java/util/List\&.size\fR
2099
2100 .fi
2101 .if n \{\
2102 .RE
2103 .\}
2104 Note that the full class name is specified, including all packages and subpackages separated by a slash (\fB/\fR)\&. For easier cut and paste operations, it is also possible to use the method name format produced by the
2105 \fB\-XX:+PrintCompilation\fR
2106 and
2107 \fB\-XX:+LogCompilation\fR
2108 options:
2109 .sp
2110 .if n \{\
2111 .RS 4
2112 .\}
2113 .nf
2114 \fB\-XX:CompileOnly=java\&.lang\&.String::length,java\&.util\&.List::size\fR
2115
2116 .fi
2117 .if n \{\
2118 .RE
2119 .\}
2120 Although wildcards are not supported, you can specify only the class or package name to compile all methods in that class or package, as well as specify just the method to compile methods with this name in any class:
2121 .sp
2122 .if n \{\
2123 .RS 4
2124 .\}
2125 .nf
2126 \fB\-XX:CompileOnly=java/lang/String\fR
2127 \fB\-XX:CompileOnly=java/lang\fR
2128 \fB\-XX:CompileOnly=\&.length\fR
2129
2130 .fi
2131 .if n \{\
2132 .RE
2133 .\}
2134 .RE
2135 .PP
2136 \-XX:CompileThreshold=\fIinvocations\fR
2137 .RS 4
2138 Sets the number of interpreted method invocations before compilation\&. By default, in the server JVM, the JIT compiler performs 10,000 interpreted method invocations to gather information for efficient compilation\&. For the client JVM, the default setting is 1,500 invocations\&. This option is ignored when tiered compilation is enabled; see the option
2139 \fB\-XX:+TieredCompilation\fR\&. The following example shows how to set the number of interpreted method invocations to 5,000:
2140 .sp
2141 .if n \{\
2142 .RS 4
2143 .\}
2144 .nf
2145 \fB\-XX:CompileThreshold=5000\fR
2146
2147 .fi
2148 .if n \{\
2149 .RE
2150 .\}
2151 You can completely disable interpretation of Java methods before compilation by specifying the
2152 \fB\-Xcomp\fR
2153 option\&.
2154 .RE
2155 .PP
2156 \-XX:+DoEscapeAnalysis
2157 .RS 4
2158 Enables the use of escape analysis\&. This option is enabled by default\&. To disable the use of escape analysis, specify
2159 \fB\-XX:\-DoEscapeAnalysis\fR\&. Only the Java HotSpot Server VM supports this option\&.
2160 .RE
2161 .PP
2162 \-XX:InitialCodeCacheSize=\fIsize\fR
2163 .RS 4
2164 Sets the initial code cache size (in bytes)\&. Append the letter
2165 \fBk\fR
2166 or
2167 \fBK\fR
2168 to indicate kilobytes,
2169 \fBm\fR
2170 or
2171 \fBM\fR
2172 to indicate megabytes,
2173 \fBg\fR
2174 or
2175 \fBG\fR
2176 to indicate gigabytes\&. The default value is set to 500 KB\&. The initial code cache size should be not less than the system\*(Aqs minimal memory page size\&. The following example shows how to set the initial code cache size to 32 KB:
2177 .sp
2178 .if n \{\
2179 .RS 4
2180 .\}
2181 .nf
2182 \fB\-XX:InitialCodeCacheSize=32k\fR
2183
2184 .fi
2185 .if n \{\
2186 .RE
2187 .\}
2188 .RE
2189 .PP
2190 \-XX:+Inline
2191 .RS 4
2192 Enables method inlining\&. This option is enabled by default to increase performance\&. To disable method inlining, specify
2193 \fB\-XX:\-Inline\fR\&.
2194 .RE
2195 .PP
2196 \-XX:InlineSmallCode=\fIsize\fR
2197 .RS 4
2198 Sets the maximum code size (in bytes) for compiled methods that should be inlined\&. Append the letter
2199 \fBk\fR
2200 or
2201 \fBK\fR
2202 to indicate kilobytes,
2203 \fBm\fR
2204 or
2205 \fBM\fR
2206 to indicate megabytes,
2207 \fBg\fR
2208 or
2209 \fBG\fR
2210 to indicate gigabytes\&. Only compiled methods with the size smaller than the specified size will be inlined\&. By default, the maximum code size is set to 1000 bytes:
2211 .sp
2212 .if n \{\
2213 .RS 4
2214 .\}
2215 .nf
2216 \fB\-XX:InlineSmallCode=1000\fR
2217
2218 .fi
2219 .if n \{\
2220 .RE
2221 .\}
2222 .RE
2223 .PP
2224 \-XX:+LogCompilation
2225 .RS 4
2226 Enables logging of compilation activity to a file named
2227 \fBhotspot\&.log\fR
2228 in the current working directory\&. You can specify a different log file path and name using the
2229 \fB\-XX:LogFile\fR
2230 option\&.
2231 .sp
2232 By default, this option is disabled and compilation activity is not logged\&. The
2233 \fB\-XX:+LogCompilation\fR
2234 option has to be used together with the
2235 \fB\-XX:UnlockDiagnosticVMOptions\fR
2236 option that unlocks diagnostic JVM options\&.
2237 .sp
2238 You can enable verbose diagnostic output with a message printed to the console every time a method is compiled by using the
2239 \fB\-XX:+PrintCompilation\fR
2240 option\&.
2241 .RE
2242 .PP
2243 \-XX:MaxInlineSize=\fIsize\fR
2244 .RS 4
2245 Sets the maximum bytecode size (in bytes) of a method to be inlined\&. Append the letter
2246 \fBk\fR
2247 or
2248 \fBK\fR
2249 to indicate kilobytes,
2250 \fBm\fR
2251 or
2252 \fBM\fR
2253 to indicate megabytes,
2254 \fBg\fR
2255 or
2256 \fBG\fR
2257 to indicate gigabytes\&. By default, the maximum bytecode size is set to 35 bytes:
2258 .sp
2259 .if n \{\
2260 .RS 4
2261 .\}
2262 .nf
2263 \fB\-XX:MaxInlineSize=35\fR
2264
2265 .fi
2266 .if n \{\
2267 .RE
2268 .\}
2269 .RE
2270 .PP
2271 \-XX:MaxNodeLimit=\fInodes\fR
2272 .RS 4
2273 Sets the maximum number of nodes to be used during single method compilation\&. By default, the maximum number of nodes is set to 65,000:
2274 .sp
2275 .if n \{\
2276 .RS 4
2277 .\}
2278 .nf
2279 \fB\-XX:MaxNodeLimit=65000\fR
2280
2281 .fi
2282 .if n \{\
2283 .RE
2284 .\}
2285 .RE
2286 .PP
2287 \-XX:MaxTrivialSize=\fIsize\fR
2288 .RS 4
2289 Sets the maximum bytecode size (in bytes) of a trivial method to be inlined\&. Append the letter
2290 \fBk\fR
2291 or
2292 \fBK\fR
2293 to indicate kilobytes,
2294 \fBm\fR
2295 or
2296 \fBM\fR
2297 to indicate megabytes,
2298 \fBg\fR
2299 or
2300 \fBG\fR
2301 to indicate gigabytes\&. By default, the maximum bytecode size of a trivial method is set to 6 bytes:
2302 .sp
2303 .if n \{\
2304 .RS 4
2305 .\}
2306 .nf
2307 \fB\-XX:MaxTrivialSize=6\fR
2308
2309 .fi
2310 .if n \{\
2311 .RE
2312 .\}
2313 .RE
2314 .PP
2315 \-XX:+OptimizeStringConcat
2316 .RS 4
2317 Enables the optimization of
2318 \fBString\fR
2319 concatenation operations\&. This option is enabled by default\&. To disable the optimization of
2320 \fBString\fR
2321 concatenation operations, specify
2322 \fB\-XX:\-OptimizeStringConcat\fR\&. Only the Java HotSpot Server VM supports this option\&.
2323 .RE
2324 .PP
2325 \-XX:+PrintAssembly
2326 .RS 4
2327 Enables printing of assembly code for bytecoded and native methods by using the external
2328 \fBdisassembler\&.so\fR
2329 library\&. This enables you to see the generated code, which may help you to diagnose performance issues\&.
2330 .sp
2331 By default, this option is disabled and assembly code is not printed\&. The
2332 \fB\-XX:+PrintAssembly\fR
2333 option has to be used together with the
2334 \fB\-XX:UnlockDiagnosticVMOptions\fR
2335 option that unlocks diagnostic JVM options\&.
2336 .RE
2337 .PP
2338 \-XX:+PrintCompilation
2339 .RS 4
2340 Enables verbose diagnostic output from the JVM by printing a message to the console every time a method is compiled\&. This enables you to see which methods actually get compiled\&. By default, this option is disabled and diagnostic output is not printed\&.
2341 .sp
2342 You can also log compilation activity to a file by using the
2343 \fB\-XX:+LogCompilation\fR
2344 option\&.
2345 .RE
2346 .PP
2347 \-XX:+PrintInlining
2348 .RS 4
2349 Enables printing of inlining decisions\&. This enables you to see which methods are getting inlined\&.
2350 .sp
2351 By default, this option is disabled and inlining information is not printed\&. The
2352 \fB\-XX:+PrintInlining\fR
2353 option has to be used together with the
2354 \fB\-XX:+UnlockDiagnosticVMOptions\fR
2355 option that unlocks diagnostic JVM options\&.
2356 .RE
2357 .PP
2358 \-XX:ReservedCodeCacheSize=\fIsize\fR
2359 .RS 4
2360 Sets the maximum code cache size (in bytes) for JIT\-compiled code\&. Append the letter
2361 \fBk\fR
2362 or
2363 \fBK\fR
2364 to indicate kilobytes,
2365 \fBm\fR
2366 or
2367 \fBM\fR
2368 to indicate megabytes,
2369 \fBg\fR
2370 or
2371 \fBG\fR
2372 to indicate gigabytes\&. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option
2373 \fB\-XX:\-TieredCompilation\fR, then the default size is 48 MB\&. This option has a limit of 2 GB; otherwise, an error is generated\&. The maximum code cache size should not be less than the initial code cache size; see the option
2374 \fB\-XX:InitialCodeCacheSize\fR\&. This option is equivalent to
2375 \fB\-Xmaxjitcodesize\fR\&.
2376 .RE
2377 .PP
2378 \-XX:RTMAbortRatio=\fIabort_ratio\fR
2379 .RS 4
2380 The RTM abort ratio is specified as a percentage (%) of all executed RTM transactions\&. If a number of aborted transactions becomes greater than this ratio, then the compiled code will be deoptimized\&. This ratio is used when the
2381 \fB\-XX:+UseRTMDeopt\fR
2382 option is enabled\&. The default value of this option is 50\&. This means that the compiled code will be deoptimized if 50% of all transactions are aborted\&.
2383 .RE
2384 .PP
2385 \-XX:RTMRetryCount=\fInumber_of_retries\fR
2386 .RS 4
2387 RTM locking code will be retried, when it is aborted or busy, the number of times specified by this option before falling back to the normal locking mechanism\&. The default value for this option is 5\&. The
2388 \fB\-XX:UseRTMLocking\fR
2389 option must be enabled\&.
2390 .RE
2391 .PP
2392 \-XX:\-TieredCompilation
2393 .RS 4
2394 Disables the use of tiered compilation\&. By default, this option is enabled\&. Only the Java HotSpot Server VM supports this option\&.
2395 .RE
2396 .PP
2397 \-XX:+UseAES
2398 .RS 4
2399 Enables hardware\-based AES intrinsics for Intel, AMD, and SPARC hardware\&. Intel Westmere (2010 and newer), AMD Bulldozer (2011 and newer), and SPARC (T4 and newer) are the supported hardware\&. UseAES is used in conjunction with UseAESIntrinsics\&.
2400 .RE
2401 .PP
2402 \-XX:+UseAESIntrinsics
2403 .RS 4
2404 UseAES and UseAESIntrinsics flags are enabled by default and are supported only for Java HotSpot Server VM 32\-bit and 64\-bit\&. To disable hardware\-based AES intrinsics, specify
2405 \fB\-XX:\-UseAES \-XX:\-UseAESIntrinsics\fR\&. For example, to enable hardware AES, use the following flags:
2406 .sp
2407 .if n \{\
2408 .RS 4
2409 .\}
2410 .nf
2411 \fB\-XX:+UseAES \-XX:+UseAESIntrinsics\fR
2412
2413 .fi
2414 .if n \{\
2415 .RE
2416 .\}
2417 To support UseAES and UseAESIntrinsics flags for 32\-bit and 64\-bit use
2418 \fB\-server\fR
2419 option to choose Java HotSpot Server VM\&. These flags are not supported on Client VM\&.
2420 .RE
2421 .PP
2422 \-XX:+UseCodeCacheFlushing
2423 .RS 4
2424 Enables flushing of the code cache before shutting down the compiler\&. This option is enabled by default\&. To disable flushing of the code cache before shutting down the compiler, specify
2425 \fB\-XX:\-UseCodeCacheFlushing\fR\&.
2426 .RE
2427 .PP
2428 \-XX:+UseCondCardMark
2429 .RS 4
2430 Enables checking of whether the card is already marked before updating the card table\&. This option is disabled by default and should only be used on machines with multiple sockets, where it will increase performance of Java applications that rely heavily on concurrent operations\&. Only the Java HotSpot Server VM supports this option\&.
2431 .RE
2432 .PP
2433 \-XX:+UseRTMDeopt
2434 .RS 4
2435 Auto\-tunes RTM locking depending on the abort ratio\&. This ratio is specified by
2436 \fB\-XX:RTMAbortRatio\fR
2437 option\&. If the number of aborted transactions exceeds the abort ratio, then the method containing the lock will be deoptimized and recompiled with all locks as normal locks\&. This option is disabled by default\&. The
2438 \fB\-XX:+UseRTMLocking\fR
2439 option must be enabled\&.
2440 .RE
2441 .PP
2442 \-XX:+UseRTMLocking
2443 .RS 4
2444 Generate Restricted Transactional Memory (RTM) locking code for all inflated locks, with the normal locking mechanism as the fallback handler\&. This option is disabled by default\&. Options related to RTM are only available for the Java HotSpot Server VM on x86 CPUs that support Transactional Synchronization Extensions (TSX)\&.
2445 .sp
2446 RTM is part of Intel\*(Aqs TSX, which is an x86 instruction set extension and facilitates the creation of multithreaded applications\&. RTM introduces the new instructions
2447 \fBXBEGIN\fR,
2448 \fBXABORT\fR,
2449 \fBXEND\fR, and
2450 \fBXTEST\fR\&. The
2451 \fBXBEGIN\fR
2452 and
2453 \fBXEND\fR
2454 instructions enclose a set of instructions to run as a transaction\&. If no conflict is found when running the transaction, the memory and register modifications are committed together at the
2455 \fBXEND\fR
2456 instruction\&. The
2457 \fBXABORT\fR
2458 instruction can be used to explicitly abort a transaction and the
2459 \fBXEND\fR
2460 instruction to check if a set of instructions are being run in a transaction\&.
2461 .sp
2462 A lock on a transaction is inflated when another thread tries to access the same transaction, thereby blocking the thread that did not originally request access to the transaction\&. RTM requires that a fallback set of operations be specified in case a transaction aborts or fails\&. An RTM lock is a lock that has been delegated to the TSX\*(Aqs system\&.
2463 .sp
2464 RTM improves performance for highly contended locks with low conflict in a critical region (which is code that must not be accessed by more than one thread concurrently)\&. RTM also improves the performance of coarse\-grain locking, which typically does not perform well in multithreaded applications\&. (Coarse\-grain locking is the strategy of holding locks for long periods to minimize the overhead of taking and releasing locks, while fine\-grained locking is the strategy of trying to achieve maximum parallelism by locking only when necessary and unlocking as soon as possible\&.) Also, for lightly contended locks that are used by different threads, RTM can reduce false cache line sharing, also known as cache line ping\-pong\&. This occurs when multiple threads from different processors are accessing different resources, but the resources share the same cache line\&. As a result, the processors repeatedly invalidate the cache lines of other processors, which forces them to read from main memory instead of their cache\&.
2465 .RE
2466 .PP
2467 \-XX:+UseSHA
2468 .RS 4
2469 Enables hardware\-based intrinsics for SHA crypto hash functions for SPARC hardware\&.
2470 \fBUseSHA\fR
2471 is used in conjunction with the
2472 \fBUseSHA1Intrinsics\fR,
2473 \fBUseSHA256Intrinsics\fR, and
2474 \fBUseSHA512Intrinsics\fR
2475 options\&.
2476 .sp
2477 The
2478 \fBUseSHA\fR
2479 and
2480 \fBUseSHA*Intrinsics\fR
2481 flags are enabled by default, and are supported only for Java HotSpot Server VM 64\-bit on SPARC T4 and newer\&.
2482 .sp
2483 This feature is only applicable when using the
2484 \fBsun\&.security\&.provider\&.Sun\fR
2485 provider for SHA operations\&.
2486 .sp
2487 To disable all hardware\-based SHA intrinsics, specify
2488 \fB\-XX:\-UseSHA\fR\&. To disable only a particular SHA intrinsic, use the appropriate corresponding option\&. For example:
2489 \fB\-XX:\-UseSHA256Intrinsics\fR\&.
2490 .RE
2491 .PP
2492 \-XX:+UseSHA1Intrinsics
2493 .RS 4
2494 Enables intrinsics for SHA\-1 crypto hash function\&.
2495 .RE
2496 .PP
2497 \-XX:+UseSHA256Intrinsics
2498 .RS 4
2499 Enables intrinsics for SHA\-224 and SHA\-256 crypto hash functions\&.
2500 .RE
2501 .PP
2502 \-XX:+UseSHA512Intrinsics
2503 .RS 4
2504 Enables intrinsics for SHA\-384 and SHA\-512 crypto hash functions\&.
2505 .RE
2506 .PP
2507 \-XX:+UseSuperWord
2508 .RS 4
2509 Enables the transformation of scalar operations into superword operations\&. This option is enabled by default\&. To disable the transformation of scalar operations into superword operations, specify
2510 \fB\-XX:\-UseSuperWord\fR\&. Only the Java HotSpot Server VM supports this option\&.
2511 .RE
2512 .SS "Advanced Serviceability Options"
2513 .PP
2514 These options provide the ability to gather system information and perform extensive debugging\&.
2515 .PP
2516 \-XX:+ExtendedDTraceProbes
2517 .RS 4
2518 Enables additional
2519 \fBdtrace\fR
2520 tool probes that impact the performance\&. By default, this option is disabled and
2521 \fBdtrace\fR
2522 performs only standard probes\&.
2523 .RE
2524 .PP
2525 \-XX:+HeapDumpOnOutOfMemory
2526 .RS 4
2527 Enables the dumping of the Java heap to a file in the current directory by using the heap profiler (HPROF) when a
2528 \fBjava\&.lang\&.OutOfMemoryError\fR
2529 exception is thrown\&. You can explicitly set the heap dump file path and name using the
2530 \fB\-XX:HeapDumpPath\fR
2531 option\&. By default, this option is disabled and the heap is not dumped when an
2532 \fBOutOfMemoryError\fR
2533 exception is thrown\&.
2534 .RE
2535 .PP
2536 \-XX:HeapDumpPath=\fIpath\fR
2537 .RS 4
2538 Sets the path and file name for writing the heap dump provided by the heap profiler (HPROF) when the
2539 \fB\-XX:+HeapDumpOnOutOfMemoryError\fR
2540 option is set\&. By default, the file is created in the current working directory, and it is named
2541 \fBjava_pid\fR\fIpid\fR\fB\&.hprof\fR
2542 where
2543 \fIpid\fR
2544 is the identifier of the process that caused the error\&. The following example shows how to set the default file explicitly (\fB%p\fR
2545 represents the current process identificator):
2546 .sp
2547 .if n \{\
2548 .RS 4
2549 .\}
2550 .nf
2551 \fB\-XX:HeapDumpPath=\&./java_pid%p\&.hprof\fR
2552
2553 .fi
2554 .if n \{\
2555 .RE
2556 .\}
2557 The following example shows how to set the heap dump file to
2558 \fB/var/log/java/java_heapdump\&.hprof\fR:
2559 .sp
2560 .if n \{\
2561 .RS 4
2562 .\}
2563 .nf
2564 \fB\-XX:HeapDumpPath=/var/log/java/java_heapdump\&.hprof\fR
2565
2566 .fi
2567 .if n \{\
2568 .RE
2569 .\}
2570 .RE
2571 .PP
2572 \-XX:LogFile=\fIpath\fR
2573 .RS 4
2574 Sets the path and file name where log data is written\&. By default, the file is created in the current working directory, and it is named
2575 \fBhotspot\&.log\fR\&.
2576 .sp
2577 The following example shows how to set the log file to
2578 \fB/var/log/java/hotspot\&.log\fR:
2579 .sp
2580 .if n \{\
2581 .RS 4
2582 .\}
2583 .nf
2584 \fB\-XX:LogFile=/var/log/java/hotspot\&.log\fR
2585
2586 .fi
2587 .if n \{\
2588 .RE
2589 .\}
2590 .RE
2591 .PP
2592 \-XX:+PrintClassHistogram
2593 .RS 4
2594 Enables printing of a class instance histogram after a
2595 \fBControl+C\fR
2596 event (\fBSIGTERM\fR)\&. By default, this option is disabled\&.
2597 .sp
2598 Setting this option is equivalent to running the
2599 \fBjmap \-histo\fR
2600 command, or the
2601 \fBjcmd \fR\fIpid\fR\fB GC\&.class_histogram\fR
2602 command, where
2603 \fIpid\fR
2604 is the current Java process identifier\&.
2605 .RE
2606 .PP
2607 \-XX:+PrintConcurrentLocks
2608 .RS 4
2609 Enables printing of locks after a event\&. By default, this option is disabled\&.
2610 .sp
2611 Enables printing of
2612 \fBjava\&.util\&.concurrent\fR
2613 locks after a
2614 \fBControl+C\fR
2615 event (\fBSIGTERM\fR)\&. By default, this option is disabled\&.
2616 .sp
2617 Setting this option is equivalent to running the
2618 \fBjstack \-l\fR
2619 command or the
2620 \fBjcmd \fR\fIpid\fR\fB Thread\&.print \-l\fR
2621 command, where
2622 \fIpid\fR
2623 is the current Java process identifier\&.
2624 .RE
2625 .PP
2626 \-XX:+UnlockDiagnosticVMOptions
2627 .RS 4
2628 Unlocks the options intended for diagnosing the JVM\&. By default, this option is disabled and diagnostic options are not available\&.
2629 .RE
2630 .SS "Advanced Garbage Collection Options"
2631 .PP
2632 These options control how garbage collection (GC) is performed by the Java HotSpot VM\&.
2633 .PP
2634 \-XX:+AggressiveHeap
2635 .RS 4
2636 Enables Java heap optimization\&. This sets various parameters to be optimal for long\-running jobs with intensive memory allocation, based on the configuration of the computer (RAM and CPU)\&. By default, the option is disabled and the heap is not optimized\&.
2637 .RE
2638 .PP
2639 \-XX:+AlwaysPreTouch
2640 .RS 4
2641 Enables touching of every page on the Java heap during JVM initialization\&. This gets all pages into the memory before entering the
2642 \fBmain()\fR
2643 method\&. The option can be used in testing to simulate a long\-running system with all virtual memory mapped to physical memory\&. By default, this option is disabled and all pages are committed as JVM heap space fills\&.
2644 .RE
2645 .PP
2646 \-XX:+CMSClassUnloadingEnabled
2647 .RS 4
2648 Enables class unloading when using the concurrent mark\-sweep (CMS) garbage collector\&. This option is enabled by default\&. To disable class unloading for the CMS garbage collector, specify
2649 \fB\-XX:\-CMSClassUnloadingEnabled\fR\&.
2650 .RE
2651 .PP
2652 \-XX:CMSExpAvgFactor=\fIpercent\fR
2653 .RS 4
2654 Sets the percentage of time (0 to 100) used to weight the current sample when computing exponential averages for the concurrent collection statistics\&. By default, the exponential averages factor is set to 25%\&. The following example shows how to set the factor to 15%:
2655 .sp
2656 .if n \{\
2657 .RS 4
2658 .\}
2659 .nf
2660 \fB\-XX:CMSExpAvgFactor=15\fR
2661
2662 .fi
2663 .if n \{\
2664 .RE
2665 .\}
2666 .RE
2667 .PP
2668 \-XX:CMSInitiatingOccupancyFraction=\fIpercent\fR
2669 .RS 4
2670 Sets the percentage of the old generation occupancy (0 to 100) at which to start a CMS collection cycle\&. The default value is set to \-1\&. Any negative value (including the default) implies that
2671 \fB\-XX:CMSTriggerRatio\fR
2672 is used to define the value of the initiating occupancy fraction\&.
2673 .sp
2674 The following example shows how to set the occupancy fraction to 20%:
2675 .sp
2676 .if n \{\
2677 .RS 4
2678 .\}
2679 .nf
2680 \fB\-XX:CMSInitiatingOccupancyFraction=20\fR
2681
2682 .fi
2683 .if n \{\
2684 .RE
2685 .\}
2686 .RE
2687 .PP
2688 \-XX:+CMSScavengeBeforeRemark
2689 .RS 4
2690 Enables scavenging attempts before the CMS remark step\&. By default, this option is disabled\&.
2691 .RE
2692 .PP
2693 \-XX:CMSTriggerRatio=\fIpercent\fR
2694 .RS 4
2695 Sets the percentage (0 to 100) of the value specified by
2696 \fB\-XX:MinHeapFreeRatio\fR
2697 that is allocated before a CMS collection cycle commences\&. The default value is set to 80%\&.
2698 .sp
2699 The following example shows how to set the occupancy fraction to 75%:
2700 .sp
2701 .if n \{\
2702 .RS 4
2703 .\}
2704 .nf
2705 \fB\-XX:CMSTriggerRatio=75\fR
2706
2707 .fi
2708 .if n \{\
2709 .RE
2710 .\}
2711 .RE
2712 .PP
2713 \-XX:ConcGCThreads=\fIthreads\fR
2714 .RS 4
2715 Sets the number of threads used for concurrent GC\&. The default value depends on the number of CPUs available to the JVM\&.
2716 .sp
2717 For example, to set the number of threads for concurrent GC to 2, specify the following option:
2718 .sp
2719 .if n \{\
2720 .RS 4
2721 .\}
2722 .nf
2723 \fB\-XX:ConcGCThreads=2\fR
2724
2725 .fi
2726 .if n \{\
2727 .RE
2728 .\}
2729 .RE
2730 .PP
2731 \-XX:+DisableExplicitGC
2732 .RS 4
2733 Enables the option that disables processing of calls to
2734 \fBSystem\&.gc()\fR\&. This option is disabled by default, meaning that calls to
2735 \fBSystem\&.gc()\fR
2736 are processed\&. If processing of calls to
2737 \fBSystem\&.gc()\fR
2738 is disabled, the JVM still performs GC when necessary\&.
2739 .RE
2740 .PP
2741 \-XX:+ExplicitGCInvokesConcurrent
2742 .RS 4
2743 Enables invoking of concurrent GC by using the
2744 \fBSystem\&.gc()\fR
2745 request\&. This option is disabled by default and can be enabled only together with the
2746 \fB\-XX:+UseConcMarkSweepGC\fR
2747 option\&.
2748 .RE
2749 .PP
2750 \-XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses
2751 .RS 4
2752 Enables invoking of concurrent GC by using the
2753 \fBSystem\&.gc()\fR
2754 request and unloading of classes during the concurrent GC cycle\&. This option is disabled by default and can be enabled only together with the
2755 \fB\-XX:+UseConcMarkSweepGC\fR
2756 option\&.
2757 .RE
2758 .PP
2759 \-XX:G1HeapRegionSize=\fIsize\fR
2760 .RS 4
2761 Sets the size of the regions into which the Java heap is subdivided when using the garbage\-first (G1) collector\&. The value can be between 1 MB and 32 MB\&. The default region size is determined ergonomically based on the heap size\&.
2762 .sp
2763 The following example shows how to set the size of the subdivisions to 16 MB:
2764 .sp
2765 .if n \{\
2766 .RS 4
2767 .\}
2768 .nf
2769 \fB\-XX:G1HeapRegionSize=16m\fR
2770
2771 .fi
2772 .if n \{\
2773 .RE
2774 .\}
2775 .RE
2776 .PP
2777 \-XX:+G1PrintHeapRegions
2778 .RS 4
2779 Enables the printing of information about which regions are allocated and which are reclaimed by the G1 collector\&. By default, this option is disabled\&.
2780 .RE
2781 .PP
2782 \-XX:G1ReservePercent=\fIpercent\fR
2783 .RS 4
2784 Sets the percentage of the heap (0 to 50) that is reserved as a false ceiling to reduce the possibility of promotion failure for the G1 collector\&. By default, this option is set to 10%\&.
2785 .sp
2786 The following example shows how to set the reserved heap to 20%:
2787 .sp
2788 .if n \{\
2789 .RS 4
2790 .\}
2791 .nf
2792 \fB\-XX:G1ReservePercent=20\fR
2793
2794 .fi
2795 .if n \{\
2796 .RE
2797 .\}
2798 .RE
2799 .PP
2800 \-XX:InitialHeapSize=\fIsize\fR
2801 .RS 4
2802 Sets the initial size (in bytes) of the memory allocation pool\&. This value must be either 0, or a multiple of 1024 and greater than 1 MB\&. Append the letter
2803 \fBk\fR
2804 or
2805 \fBK\fR
2806 to indicate kilobytes,
2807 \fBm\fR
2808 or
2809 \fBM\fR
2810 to indicate megabytes,
2811 \fBg\fR
2812 or
2813 \fBG\fR
2814 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. See the section "Ergonomics" in
2815 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
2816 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
2817 .sp
2818 The following examples show how to set the size of allocated memory to 6 MB using various units:
2819 .sp
2820 .if n \{\
2821 .RS 4
2822 .\}
2823 .nf
2824 \fB\-XX:InitialHeapSize=6291456\fR
2825 \fB\-XX:InitialHeapSize=6144k\fR
2826 \fB\-XX:InitialHeapSize=6m\fR
2827
2828 .fi
2829 .if n \{\
2830 .RE
2831 .\}
2832 If you set this option to 0, then the initial size will be set as the sum of the sizes allocated for the old generation and the young generation\&. The size of the heap for the young generation can be set using the
2833 \fB\-XX:NewSize\fR
2834 option\&.
2835 .RE
2836 .PP
2837 \-XX:InitialSurvivorRatio=\fIratio\fR
2838 .RS 4
2839 Sets the initial survivor space ratio used by the throughput garbage collector (which is enabled by the
2840 \fB\-XX:+UseParallelGC\fR
2841 and/or \-\fBXX:+UseParallelOldGC\fR
2842 options)\&. Adaptive sizing is enabled by default with the throughput garbage collector by using the
2843 \fB\-XX:+UseParallelGC\fR
2844 and
2845 \fB\-XX:+UseParallelOldGC\fR
2846 options, and survivor space is resized according to the application behavior, starting with the initial value\&. If adaptive sizing is disabled (using the
2847 \fB\-XX:\-UseAdaptiveSizePolicy\fR
2848 option), then the
2849 \fB\-XX:SurvivorRatio\fR
2850 option should be used to set the size of the survivor space for the entire execution of the application\&.
2851 .sp
2852 The following formula can be used to calculate the initial size of survivor space (S) based on the size of the young generation (Y), and the initial survivor space ratio (R):
2853 .sp
2854 .if n \{\
2855 .RS 4
2856 .\}
2857 .nf
2858 \fBS=Y/(R+2)\fR
2859
2860 .fi
2861 .if n \{\
2862 .RE
2863 .\}
2864 The 2 in the equation denotes two survivor spaces\&. The larger the value specified as the initial survivor space ratio, the smaller the initial survivor space size\&.
2865 .sp
2866 By default, the initial survivor space ratio is set to 8\&. If the default value for the young generation space size is used (2 MB), the initial size of the survivor space will be 0\&.2 MB\&.
2867 .sp
2868 The following example shows how to set the initial survivor space ratio to 4:
2869 .sp
2870 .if n \{\
2871 .RS 4
2872 .\}
2873 .nf
2874 \fB\-XX:InitialSurvivorRatio=4\fR
2875
2876 .fi
2877 .if n \{\
2878 .RE
2879 .\}
2880 .RE
2881 .PP
2882 \-XX:InitiatingHeapOccupancyPercent=\fIpercent\fR
2883 .RS 4
2884 Sets the percentage of the heap occupancy (0 to 100) at which to start a concurrent GC cycle\&. It is used by garbage collectors that trigger a concurrent GC cycle based on the occupancy of the entire heap, not just one of the generations (for example, the G1 garbage collector)\&.
2885 .sp
2886 By default, the initiating value is set to 45%\&. A value of 0 implies nonstop GC cycles\&. The following example shows how to set the initiating heap occupancy to 75%:
2887 .sp
2888 .if n \{\
2889 .RS 4
2890 .\}
2891 .nf
2892 \fB\-XX:InitiatingHeapOccupancyPercent=75\fR
2893
2894 .fi
2895 .if n \{\
2896 .RE
2897 .\}
2898 .RE
2899 .PP
2900 \-XX:MaxGCPauseMillis=\fItime\fR
2901 .RS 4
2902 Sets a target for the maximum GC pause time (in milliseconds)\&. This is a soft goal, and the JVM will make its best effort to achieve it\&. By default, there is no maximum pause time value\&.
2903 .sp
2904 The following example shows how to set the maximum target pause time to 500 ms:
2905 .sp
2906 .if n \{\
2907 .RS 4
2908 .\}
2909 .nf
2910 \fB\-XX:MaxGCPauseMillis=500\fR
2911
2912 .fi
2913 .if n \{\
2914 .RE
2915 .\}
2916 .RE
2917 .PP
2918 \-XX:MaxHeapSize=\fIsize\fR
2919 .RS 4
2920 Sets the maximum size (in byes) of the memory allocation pool\&. This value must be a multiple of 1024 and greater than 2 MB\&. Append the letter
2921 \fBk\fR
2922 or
2923 \fBK\fR
2924 to indicate kilobytes,
2925 \fBm\fR
2926 or
2927 \fBM\fR
2928 to indicate megabytes,
2929 \fBg\fR
2930 or
2931 \fBG\fR
2932 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. For server deployments,
2933 \fB\-XX:InitialHeapSize\fR
2934 and
2935 \fB\-XX:MaxHeapSize\fR
2936 are often set to the same value\&. See the section "Ergonomics" in
2937 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
2938 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
2939 .sp
2940 The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:
2941 .sp
2942 .if n \{\
2943 .RS 4
2944 .\}
2945 .nf
2946 \fB\-XX:MaxHeapSize=83886080\fR
2947 \fB\-XX:MaxHeapSize=81920k\fR
2948 \fB\-XX:MaxHeapSize=80m\fR
2949
2950 .fi
2951 .if n \{\
2952 .RE
2953 .\}
2954 On Oracle Solaris 7 and Oracle Solaris 8 SPARC platforms, the upper limit for this value is approximately 4,000 MB minus overhead amounts\&. On Oracle Solaris 2\&.6 and x86 platforms, the upper limit is approximately 2,000 MB minus overhead amounts\&. On Linux platforms, the upper limit is approximately 2,000 MB minus overhead amounts\&.
2955 .sp
2956 The
2957 \fB\-XX:MaxHeapSize\fR
2958 option is equivalent to
2959 \fB\-Xmx\fR\&.
2960 .RE
2961 .PP
2962 \-XX:MaxHeapFreeRatio=\fIpercent\fR
2963 .RS 4
2964 Sets the maximum allowed percentage of free heap space (0 to 100) after a GC event\&. If free heap space expands above this value, then the heap will be shrunk\&. By default, this value is set to 70%\&.
2965 .sp
2966 The following example shows how to set the maximum free heap ratio to 75%:
2967 .sp
2968 .if n \{\
2969 .RS 4
2970 .\}
2971 .nf
2972 \fB\-XX:MaxHeapFreeRatio=75\fR
2973
2974 .fi
2975 .if n \{\
2976 .RE
2977 .\}
2978 .RE
2979 .PP
2980 \-XX:MaxMetaspaceSize=\fIsize\fR
2981 .RS 4
2982 Sets the maximum amount of native memory that can be allocated for class metadata\&. By default, the size is not limited\&. The amount of metadata for an application depends on the application itself, other running applications, and the amount of memory available on the system\&.
2983 .sp
2984 The following example shows how to set the maximum class metadata size to 256 MB:
2985 .sp
2986 .if n \{\
2987 .RS 4
2988 .\}
2989 .nf
2990 \fB\-XX:MaxMetaspaceSize=256m\fR
2991
2992 .fi
2993 .if n \{\
2994 .RE
2995 .\}
2996 .RE
2997 .PP
2998 \-XX:MaxNewSize=\fIsize\fR
2999 .RS 4
3000 Sets the maximum size (in bytes) of the heap for the young generation (nursery)\&. The default value is set ergonomically\&.
3001 .RE
3002 .PP
3003 \-XX:MaxTenuringThreshold=\fIthreshold\fR
3004 .RS 4
3005 Sets the maximum tenuring threshold for use in adaptive GC sizing\&. The largest value is 15\&. The default value is 15 for the parallel (throughput) collector, and 6 for the CMS collector\&.
3006 .sp
3007 The following example shows how to set the maximum tenuring threshold to 10:
3008 .sp
3009 .if n \{\
3010 .RS 4
3011 .\}
3012 .nf
3013 \fB\-XX:MaxTenuringThreshold=10\fR
3014
3015 .fi
3016 .if n \{\
3017 .RE
3018 .\}
3019 .RE
3020 .PP
3021 \-XX:MetaspaceSize=\fIsize\fR
3022 .RS 4
3023 Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded\&. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used\&. The default size depends on the platform\&.
3024 .RE
3025 .PP
3026 \-XX:MinHeapFreeRatio=\fIpercent\fR
3027 .RS 4
3028 Sets the minimum allowed percentage of free heap space (0 to 100) after a GC event\&. If free heap space falls below this value, then the heap will be expanded\&. By default, this value is set to 40%\&.
3029 .sp
3030 The following example shows how to set the minimum free heap ratio to 25%:
3031 .sp
3032 .if n \{\
3033 .RS 4
3034 .\}
3035 .nf
3036 \fB\-XX:MinHeapFreeRatio=25\fR
3037
3038 .fi
3039 .if n \{\
3040 .RE
3041 .\}
3042 .RE
3043 .PP
3044 \-XX:NewRatio=\fIratio\fR
3045 .RS 4
3046 Sets the ratio between young and old generation sizes\&. By default, this option is set to 2\&. The following example shows how to set the young/old ratio to 1:
3047 .sp
3048 .if n \{\
3049 .RS 4
3050 .\}
3051 .nf
3052 \fB\-XX:NewRatio=1\fR
3053
3054 .fi
3055 .if n \{\
3056 .RE
3057 .\}
3058 .RE
3059 .PP
3060 \-XX:NewSize=\fIsize\fR
3061 .RS 4
3062 Sets the initial size (in bytes) of the heap for the young generation (nursery)\&. Append the letter
3063 \fBk\fR
3064 or
3065 \fBK\fR
3066 to indicate kilobytes,
3067 \fBm\fR
3068 or
3069 \fBM\fR
3070 to indicate megabytes,
3071 \fBg\fR
3072 or
3073 \fBG\fR
3074 to indicate gigabytes\&.
3075 .sp
3076 The young generation region of the heap is used for new objects\&. GC is performed in this region more often than in other regions\&. If the size for the young generation is too low, then a large number of minor GCs will be performed\&. If the size is too high, then only full GCs will be performed, which can take a long time to complete\&. Oracle recommends that you keep the size for the young generation between a half and a quarter of the overall heap size\&.
3077 .sp
3078 The following examples show how to set the initial size of young generation to 256 MB using various units:
3079 .sp
3080 .if n \{\
3081 .RS 4
3082 .\}
3083 .nf
3084 \fB\-XX:NewSize=256m\fR
3085 \fB\-XX:NewSize=262144k\fR
3086 \fB\-XX:NewSize=268435456\fR
3087
3088 .fi
3089 .if n \{\
3090 .RE
3091 .\}
3092 The
3093 \fB\-XX:NewSize\fR
3094 option is equivalent to
3095 \fB\-Xmn\fR\&.
3096 .RE
3097 .PP
3098 \-XX:ParallelGCThreads=\fIthreads\fR
3099 .RS 4
3100 Sets the number of threads used for parallel garbage collection in the young and old generations\&. The default value depends on the number of CPUs available to the JVM\&.
3101 .sp
3102 For example, to set the number of threads for parallel GC to 2, specify the following option:
3103 .sp
3104 .if n \{\
3105 .RS 4
3106 .\}
3107 .nf
3108 \fB\-XX:ParallelGCThreads=2\fR
3109
3110 .fi
3111 .if n \{\
3112 .RE
3113 .\}
3114 .RE
3115 .PP
3116 \-XX:+ParallelRefProcEnabled
3117 .RS 4
3118 Enables parallel reference processing\&. By default, this option is disabled\&.
3119 .RE
3120 .PP
3121 \-XX:+PrintAdaptiveSizePolicy
3122 .RS 4
3123 Enables printing of information about adaptive generation sizing\&. By default, this option is disabled\&.
3124 .RE
3125 .PP
3126 \-XX:+PrintGC
3127 .RS 4
3128 Enables printing of messages at every GC\&. By default, this option is disabled\&.
3129 .RE
3130 .PP
3131 \-XX:+PrintGCApplicationConcurrentTime
3132 .RS 4
3133 Enables printing of how much time elapsed since the last pause (for example, a GC pause)\&. By default, this option is disabled\&.
3134 .RE
3135 .PP
3136 \-XX:+PrintGCApplicationStoppedTime
3137 .RS 4
3138 Enables printing of how much time the pause (for example, a GC pause) lasted\&. By default, this option is disabled\&.
3139 .RE
3140 .PP
3141 \-XX:+PrintGCDateStamps
3142 .RS 4
3143 Enables printing of a date stamp at every GC\&. By default, this option is disabled\&.
3144 .RE
3145 .PP
3146 \-XX:+PrintGCDetails
3147 .RS 4
3148 Enables printing of detailed messages at every GC\&. By default, this option is disabled\&.
3149 .RE
3150 .PP
3151 \-XX:+PrintGCTaskTimeStamps
3152 .RS 4
3153 Enables printing of time stamps for every individual GC worker thread task\&. By default, this option is disabled\&.
3154 .RE
3155 .PP
3156 \-XX:+PrintGCTimeStamps
3157 .RS 4
3158 Enables printing of time stamps at every GC\&. By default, this option is disabled\&.
3159 .RE
3160 .PP
3161 \-XX:+PrintStringDeduplicationStatistics
3162 .RS 4
3163 Prints detailed deduplication statistics\&. By default, this option is disabled\&. See the
3164 \fB\-XX:+UseStringDeduplication\fR
3165 option\&.
3166 .RE
3167 .PP
3168 \-XX:+PrintTenuringDistribution
3169 .RS 4
3170 Enables printing of tenuring age information\&. The following is an example of the output:
3171 .sp
3172 .if n \{\
3173 .RS 4
3174 .\}
3175 .nf
3176 \fBDesired survivor size 48286924 bytes, new threshold 10 (max 10)\fR
3177 \fB\- age 1: 28992024 bytes, 28992024 total\fR
3178 \fB\- age 2: 1366864 bytes, 30358888 total\fR
3179 \fB\- age 3: 1425912 bytes, 31784800 total\fR
3180 \fB\&.\&.\&.\fR
3181
3182 .fi
3183 .if n \{\
3184 .RE
3185 .\}
3186 Age 1 objects are the youngest survivors (they were created after the previous scavenge, survived the latest scavenge, and moved from eden to survivor space)\&. Age 2 objects have survived two scavenges (during the second scavenge they were copied from one survivor space to the next)\&. And so on\&.
3187 .sp
3188 In the preceding example, 28 992 024 bytes survived one scavenge and were copied from eden to survivor space, 1 366 864 bytes are occupied by age 2 objects, etc\&. The third value in each row is the cumulative size of objects of age n or less\&.
3189 .sp
3190 By default, this option is disabled\&.
3191 .RE
3192 .PP
3193 \-XX:+ScavengeBeforeFullGC
3194 .RS 4
3195 Enables GC of the young generation before each full GC\&. This option is enabled by default\&. Oracle recommends that you
3196 \fIdo not\fR
3197 disable it, because scavenging the young generation before a full GC can reduce the number of objects reachable from the old generation space into the young generation space\&. To disable GC of the young generation before each full GC, specify
3198 \fB\-XX:\-ScavengeBeforeFullGC\fR\&.
3199 .RE
3200 .PP
3201 \-XX:SoftRefLRUPolicyMSPerMB=\fItime\fR
3202 .RS 4
3203 Sets the amount of time (in milliseconds) a softly reachable object is kept active on the heap after the last time it was referenced\&. The default value is one second of lifetime per free megabyte in the heap\&. The
3204 \fB\-XX:SoftRefLRUPolicyMSPerMB\fR
3205 option accepts integer values representing milliseconds per one megabyte of the current heap size (for Java HotSpot Client VM) or the maximum possible heap size (for Java HotSpot Server VM)\&. This difference means that the Client VM tends to flush soft references rather than grow the heap, whereas the Server VM tends to grow the heap rather than flush soft references\&. In the latter case, the value of the
3206 \fB\-Xmx\fR
3207 option has a significant effect on how quickly soft references are garbage collected\&.
3208 .sp
3209 The following example shows how to set the value to 2\&.5 seconds:
3210 .sp
3211 .if n \{\
3212 .RS 4
3213 .\}
3214 .nf
3215 \fB\-XX:SoftRefLRUPolicyMSPerMB=2500\fR
3216
3217 .fi
3218 .if n \{\
3219 .RE
3220 .\}
3221 .RE
3222 .PP
3223 \-XX:StringDeduplicationAgeThreshold=\fIthreshold\fR
3224 .RS 4
3225 \fBString\fR
3226 objects reaching the specified age are considered candidates for deduplication\&. An object\*(Aqs age is a measure of how many times it has survived garbage collection\&. This is sometimes referred to as tenuring; see the
3227 \fB\-XX:+PrintTenuringDistribution\fR
3228 option\&. Note that
3229 \fBString\fR
3230 objects that are promoted to an old heap region before this age has been reached are always considered candidates for deduplication\&. The default value for this option is
3231 \fB3\fR\&. See the
3232 \fB\-XX:+UseStringDeduplication\fR
3233 option\&.
3234 .RE
3235 .PP
3236 \-XX:SurvivorRatio=\fIratio\fR
3237 .RS 4
3238 Sets the ratio between eden space size and survivor space size\&. By default, this option is set to 8\&. The following example shows how to set the eden/survivor space ratio to 4:
3239 .sp
3240 .if n \{\
3241 .RS 4
3242 .\}
3243 .nf
3244 \fB\-XX:SurvivorRatio=4\fR
3245
3246 .fi
3247 .if n \{\
3248 .RE
3249 .\}
3250 .RE
3251 .PP
3252 \-XX:TargetSurvivorRatio=\fIpercent\fR
3253 .RS 4
3254 Sets the desired percentage of survivor space (0 to 100) used after young garbage collection\&. By default, this option is set to 50%\&.
3255 .sp
3256 The following example shows how to set the target survivor space ratio to 30%:
3257 .sp
3258 .if n \{\
3259 .RS 4
3260 .\}
3261 .nf
3262 \fB\-XX:TargetSurvivorRatio=30\fR
3263
3264 .fi
3265 .if n \{\
3266 .RE
3267 .\}
3268 .RE
3269 .PP
3270 \-XX:TLABSize=\fIsize\fR
3271 .RS 4
3272 Sets the initial size (in bytes) of a thread\-local allocation buffer (TLAB)\&. Append the letter
3273 \fBk\fR
3274 or
3275 \fBK\fR
3276 to indicate kilobytes,
3277 \fBm\fR
3278 or
3279 \fBM\fR
3280 to indicate megabytes,
3281 \fBg\fR
3282 or
3283 \fBG\fR
3284 to indicate gigabytes\&. If this option is set to 0, then the JVM chooses the initial size automatically\&.
3285 .sp
3286 The following example shows how to set the initial TLAB size to 512 KB:
3287 .sp
3288 .if n \{\
3289 .RS 4
3290 .\}
3291 .nf
3292 \fB\-XX:TLABSize=512k\fR
3293
3294 .fi
3295 .if n \{\
3296 .RE
3297 .\}
3298 .RE
3299 .PP
3300 \-XX:+UseAdaptiveSizePolicy
3301 .RS 4
3302 Enables the use of adaptive generation sizing\&. This option is enabled by default\&. To disable adaptive generation sizing, specify
3303 \fB\-XX:\-UseAdaptiveSizePolicy\fR
3304 and set the size of the memory allocation pool explicitly (see the
3305 \fB\-XX:SurvivorRatio\fR
3306 option)\&.
3307 .RE
3308 .PP
3309 \-XX:+UseCMSInitiatingOccupancyOnly
3310 .RS 4
3311 Enables the use of the occupancy value as the only criterion for initiating the CMS collector\&. By default, this option is disabled and other criteria may be used\&.
3312 .RE
3313 .PP
3314 \-XX:+UseConcMarkSweepGC
3315 .RS 4
3316 Enables the use of the CMS garbage collector for the old generation\&. Oracle recommends that you use the CMS garbage collector when application latency requirements cannot be met by the throughput (\fB\-XX:+UseParallelGC\fR) garbage collector\&. The G1 garbage collector (\fB\-XX:+UseG1GC\fR) is another alternative\&.
3317 .sp
3318 By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM\&. When this option is enabled, the
3319 \fB\-XX:+UseParNewGC\fR
3320 option is automatically set and you should not disable it, because the following combination of options has been deprecated in JDK 8:
3321 \fB\-XX:+UseConcMarkSweepGC \-XX:\-UseParNewGC\fR\&.
3322 .RE
3323 .PP
3324 \-XX:+UseG1GC
3325 .RS 4
3326 Enables the use of the garbage\-first (G1) garbage collector\&. It is a server\-style garbage collector, targeted for multiprocessor machines with a large amount of RAM\&. It meets GC pause time goals with high probability, while maintaining good throughput\&. The G1 collector is recommended for applications requiring large heaps (sizes of around 6 GB or larger) with limited GC latency requirements (stable and predictable pause time below 0\&.5 seconds)\&.
3327 .sp
3328 By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM\&.
3329 .RE
3330 .PP
3331 \-XX:+UseGCOverheadLimit
3332 .RS 4
3333 Enables the use of a policy that limits the proportion of time spent by the JVM on GC before an
3334 \fBOutOfMemoryError\fR
3335 exception is thrown\&. This option is enabled, by default and the parallel GC will throw an
3336 \fBOutOfMemoryError\fR
3337 if more than 98% of the total time is spent on garbage collection and less than 2% of the heap is recovered\&. When the heap is small, this feature can be used to prevent applications from running for long periods of time with little or no progress\&. To disable this option, specify
3338 \fB\-XX:\-UseGCOverheadLimit\fR\&.
3339 .RE
3340 .PP
3341 \-XX:+UseNUMA
3342 .RS 4
3343 Enables performance optimization of an application on a machine with nonuniform memory architecture (NUMA) by increasing the application\*(Aqs use of lower latency memory\&. By default, this option is disabled and no optimization for NUMA is made\&. The option is only available when the parallel garbage collector is used (\fB\-XX:+UseParallelGC\fR)\&.
3344 .RE
3345 .PP
3346 \-XX:+UseParallelGC
3347 .RS 4
3348 Enables the use of the parallel scavenge garbage collector (also known as the throughput collector) to improve the performance of your application by leveraging multiple processors\&.
3349 .sp
3350 By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM\&. If it is enabled, then the
3351 \fB\-XX:+UseParallelOldGC\fR
3352 option is automatically enabled, unless you explicitly disable it\&.
3353 .RE
3354 .PP
3355 \-XX:+UseParallelOldGC
3356 .RS 4
3357 Enables the use of the parallel garbage collector for full GCs\&. By default, this option is disabled\&. Enabling it automatically enables the
3358 \fB\-XX:+UseParallelGC\fR
3359 option\&.
3360 .RE
3361 .PP
3362 \-XX:+UseParNewGC
3363 .RS 4
3364 Enables the use of parallel threads for collection in the young generation\&. By default, this option is disabled\&. It is automatically enabled when you set the
3365 \fB\-XX:+UseConcMarkSweepGC\fR
3366 option\&. Using the
3367 \fB\-XX:+UseParNewGC\fR
3368 option without the
3369 \fB\-XX:+UseConcMarkSweepGC\fR
3370 option was deprecated in JDK 8\&.
3371 .RE
3372 .PP
3373 \-XX:+UseSerialGC
3374 .RS 4
3375 Enables the use of the serial garbage collector\&. This is generally the best choice for small and simple applications that do not require any special functionality from garbage collection\&. By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM\&.
3376 .RE
3377 .PP
3378 \-XX:+UseSHM
3379 .RS 4
3380 On Linux, enables the JVM to use shared memory to setup large pages\&.
3381 .sp
3382 For more information, see "Large Pages"\&.
3383 .RE
3384 .PP
3385 \-XX:+UseStringDeduplication
3386 .RS 4
3387 Enables string deduplication\&. By default, this option is disabled\&. To use this option, you must enable the garbage\-first (G1) garbage collector\&. See the
3388 \fB\-XX:+UseG1GC\fR
3389 option\&.
3390 .sp
3391 \fIString deduplication\fR
3392 reduces the memory footprint of
3393 \fBString\fR
3394 objects on the Java heap by taking advantage of the fact that many
3395 \fBString\fR
3396 objects are identical\&. Instead of each
3397 \fBString\fR
3398 object pointing to its own character array, identical
3399 \fBString\fR
3400 objects can point to and share the same character array\&.
3401 .RE
3402 .PP
3403 \-XX:+UseTLAB
3404 .RS 4
3405 Enables the use of thread\-local allocation blocks (TLABs) in the young generation space\&. This option is enabled by default\&. To disable the use of TLABs, specify
3406 \fB\-XX:\-UseTLAB\fR\&.
3407 .RE
3408 .SS "Deprecated and Removed Options"
3409 .PP
3410 These options were included in the previous release, but have since been considered unnecessary\&.
3411 .PP
3412 \-Xincgc
3413 .RS 4
3414 Enables incremental garbage collection\&. This option was deprecated in JDK 8 with no replacement\&.
3415 .RE
3416 .PP
3417 \-Xrun\fIlibname\fR
3418 .RS 4
3419 Loads the specified debugging/profiling library\&. This option was superseded by the
3420 \fB\-agentlib\fR
3421 option\&.
3422 .RE
3423 .PP
3424 \-XX:CMSIncrementalDutyCycle=\fIpercent\fR
3425 .RS 4
3426 Sets the percentage of time (0 to 100) between minor collections that the concurrent collector is allowed to run\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3427 \fB\-XX:+CMSIncrementalMode\fR
3428 option\&.
3429 .RE
3430 .PP
3431 \-XX:CMSIncrementalDutyCycleMin=\fIpercent\fR
3432 .RS 4
3433 Sets the percentage of time (0 to 100) between minor collections that is the lower bound for the duty cycle when
3434 \fB\-XX:+CMSIncrementalPacing\fR
3435 is enabled\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3436 \fB\-XX:+CMSIncrementalMode\fR
3437 option\&.
3438 .RE
3439 .PP
3440 \-XX:+CMSIncrementalMode
3441 .RS 4
3442 Enables the incremental mode for the CMS collector\&. This option was deprecated in JDK 8 with no replacement, along with other options that start with
3443 \fBCMSIncremental\fR\&.
3444 .RE
3445 .PP
3446 \-XX:CMSIncrementalOffset=\fIpercent\fR
3447 .RS 4
3448 Sets the percentage of time (0 to 100) by which the incremental mode duty cycle is shifted to the right within the period between minor collections\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3449 \fB\-XX:+CMSIncrementalMode\fR
3450 option\&.
3451 .RE
3452 .PP
3453 \-XX:+CMSIncrementalPacing
3454 .RS 4
3455 Enables automatic adjustment of the incremental mode duty cycle based on statistics collected while the JVM is running\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3456 \fB\-XX:+CMSIncrementalMode\fR
3457 option\&.
3458 .RE
3459 .PP
3460 \-XX:CMSIncrementalSafetyFactor=\fIpercent\fR
3461 .RS 4
3462 Sets the percentage of time (0 to 100) used to add conservatism when computing the duty cycle\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3463 \fB\-XX:+CMSIncrementalMode\fR
3464 option\&.
3465 .RE
3466 .PP
3467 \-XX:CMSInitiatingPermOccupancyFraction=\fIpercent\fR
3468 .RS 4
3469 Sets the percentage of the permanent generation occupancy (0 to 100) at which to start a GC\&. This option was deprecated in JDK 8 with no replacement\&.
3470 .RE
3471 .PP
3472 \-XX:MaxPermSize=\fIsize\fR
3473 .RS 4
3474 Sets the maximum permanent generation space size (in bytes)\&. This option was deprecated in JDK 8, and superseded by the
3475 \fB\-XX:MaxMetaspaceSize\fR
3476 option\&.
3477 .RE
3478 .PP
3479 \-XX:PermSize=\fIsize\fR
3480 .RS 4
3481 Sets the space (in bytes) allocated to the permanent generation that triggers a garbage collection if it is exceeded\&. This option was deprecated un JDK 8, and superseded by the
3482 \fB\-XX:MetaspaceSize\fR
3483 option\&.
3484 .RE
3485 .PP
3486 \-XX:+UseSplitVerifier
3487 .RS 4
3488 Enables splitting of the verification process\&. By default, this option was enabled in the previous releases, and verification was split into two phases: type referencing (performed by the compiler) and type checking (performed by the JVM runtime)\&. This option was deprecated in JDK 8, and verification is now split by default without a way to disable it\&.
3489 .RE
3490 .PP
3491 \-XX:+UseStringCache
3492 .RS 4
3493 Enables caching of commonly allocated strings\&. This option was removed from JDK 8 with no replacement\&.
3494 .RE
3495 .SH "PERFORMANCE TUNING EXAMPLES"
3496 .PP
3497 The following examples show how to use experimental tuning flags to either optimize throughput or to provide lower response time\&.
3498 .PP
3499 \fBExample 1 \fRTuning for Higher Throughput
3500 .RS 4
3501 .sp
3502 .if n \{\
3503 .RS 4
3504 .\}
3505 .nf
3506 \fBjava \-d64 \-server \-XX:+AggressiveOpts \-XX:+UseLargePages \-Xmn10g \-Xms26g \-Xmx26g\fR
3507
3508 .fi
3509 .if n \{\
3510 .RE
3511 .\}
3512 .RE
3513 .PP
3514 \fBExample 2 \fRTuning for Lower Response Time
3515 .RS 4
3516 .sp
3517 .if n \{\
3518 .RS 4
3519 .\}
3520 .nf
3521 \fBjava \-d64 \-XX:+UseG1GC \-Xms26g Xmx26g \-XX:MaxGCPauseMillis=500 \-XX:+PrintGCTimeStamp\fR
3522
3523 .fi
3524 .if n \{\
3525 .RE
3526 .\}
3527 .RE
3528 .SH "LARGE PAGES"
3529 .PP
3530 Also known as huge pages, large pages are memory pages that are significantly larger than the standard memory page size (which varies depending on the processor and operating system)\&. Large pages optimize processor Translation\-Lookaside Buffers\&.
3531 .PP
3532 A Translation\-Lookaside Buffer (TLB) is a page translation cache that holds the most\-recently used virtual\-to\-physical address translations\&. TLB is a scarce system resource\&. A TLB miss can be costly as the processor must then read from the hierarchical page table, which may require multiple memory accesses\&. By using a larger memory page size, a single TLB entry can represent a larger memory range\&. There will be less pressure on TLB, and memory\-intensive applications may have better performance\&.
3533 .PP
3534 However, large pages page memory can negatively affect system performance\&. For example, when a large mount of memory is pinned by an application, it may create a shortage of regular memory and cause excessive paging in other applications and slow down the entire system\&. Also, a system that has been up for a long time could produce excessive fragmentation, which could make it impossible to reserve enough large page memory\&. When this happens, either the OS or JVM reverts to using regular pages\&.
3535 .SS "Large Pages Support"
3536 .PP
3537 Solaris and Linux support large pages\&.
3538 .sp
3539 .it 1 an-trap
3540 .nr an-no-space-flag 1
3541 .nr an-break-flag 1
3542 .br
3543 .ps +1
3544 \fBSolaris\fR
3545 .RS 4
3546 .PP
3547 Solaris 9 and later include Multiple Page Size Support (MPSS); no additional configuration is necessary\&. See http://www\&.oracle\&.com/technetwork/server\-storage/solaris10/overview/solaris9\-features\-scalability\-135663\&.html\&.
3548 .RE
3549 .sp
3550 .it 1 an-trap
3551 .nr an-no-space-flag 1
3552 .nr an-break-flag 1
3553 .br
3554 .ps +1
3555 \fBLinux\fR
3556 .RS 4
3557 .PP
3558 The 2\&.6 kernel supports large pages\&. Some vendors have backported the code to their 2\&.4\-based releases\&. To check if your system can support large page memory, try the following:
3559 .sp
3560 .if n \{\
3561 .RS 4
3562 .\}
3563 .nf
3564 \fB# cat /proc/meminfo | grep Huge\fR
3565 \fBHugePages_Total: 0\fR
3566 \fBHugePages_Free: 0\fR
3567 \fBHugepagesize: 2048 kB\fR
3568
3569 .fi
3570 .if n \{\
3571 .RE
3572 .\}
3573 .PP
3574 If the output shows the three "Huge" variables, then your system can support large page memory but it needs to be configured\&. If the command prints nothing, then your system does not support large pages\&. To configure the system to use large page memory, login as
3575 \fBroot\fR, and then follow these steps:
3576 .sp
3577 .RS 4
3578 .ie n \{\
3579 \h'-04' 1.\h'+01'\c
3580 .\}
3581 .el \{\
3582 .sp -1
3583 .IP " 1." 4.2
3584 .\}
3585 If you are using the option
3586 \fB\-XX:+UseSHM\fR
3587 (instead of
3588 \fB\-XX:+UseHugeTLBFS\fR), then increase the
3589 \fBSHMMAX\fR
3590 value\&. It must be larger than the Java heap size\&. On a system with 4 GB of physical RAM (or less), the following will make all the memory sharable:
3591 .sp
3592 .if n \{\
3593 .RS 4
3594 .\}
3595 .nf
3596 \fB# echo 4294967295 > /proc/sys/kernel/shmmax\fR
3597
3598 .fi
3599 .if n \{\
3600 .RE
3601 .\}
3602 .RE
3603 .sp
3604 .RS 4
3605 .ie n \{\
3606 \h'-04' 2.\h'+01'\c
3607 .\}
3608 .el \{\
3609 .sp -1
3610 .IP " 2." 4.2
3611 .\}
3612 If you are using the option
3613 \fB\-XX:+UseSHM\fR
3614 or
3615 \fB\-XX:+UseHugeTLBFS\fR, then specify the number of large pages\&. In the following example, 3 GB of a 4 GB system are reserved for large pages (assuming a large page size of 2048kB, then 3 GB = 3 * 1024 MB = 3072 MB = 3072 * 1024 kB = 3145728 kB and 3145728 kB / 2048 kB = 1536):
3616 .sp
3617 .if n \{\
3618 .RS 4
3619 .\}
3620 .nf
3621 \fB# echo 1536 > /proc/sys/vm/nr_hugepages\fR
3622
3623 .fi
3624 .if n \{\
3625 .RE
3626 .\}
3627 .RE
3628 .if n \{\
3629 .sp
3630 .\}
3631 .RS 4
3632 .it 1 an-trap
3633 .nr an-no-space-flag 1
3634 .nr an-break-flag 1
3635 .br
3636 .ps +1
3637 \fBNote\fR
3638 .ps -1
3639 .br
3640 .TS
3641 allbox tab(:);
3642 l.
3643 T{
3644 .sp
3645 .RS 4
3646 .ie n \{\
3647 \h'-04'\(bu\h'+03'\c
3648 .\}
3649 .el \{\
3650 .sp -1
3651 .IP \(bu 2.3
3652 .\}
3653 Note that the values contained in
3654 \fB/proc\fR
3655 will reset after you reboot your system, so may want to set them in an initialization script (for example,
3656 \fBrc\&.local\fR
3657 or
3658 \fBsysctl\&.conf\fR)\&.
3659 .RE
3660 .sp
3661 .RS 4
3662 .ie n \{\
3663 \h'-04'\(bu\h'+03'\c
3664 .\}
3665 .el \{\
3666 .sp -1
3667 .IP \(bu 2.3
3668 .\}
3669 If you configure (or resize) the OS kernel parameters
3670 \fB/proc/sys/kernel/shmmax\fR
3671 or
3672 \fB/proc/sys/vm/nr_hugepages\fR, Java processes may allocate large pages for areas in addition to the Java heap\&. These steps can allocate large pages for the following areas:
3673 .sp
3674 .RS 4
3675 .ie n \{\
3676 \h'-04'\(bu\h'+03'\c
3677 .\}
3678 .el \{\
3679 .sp -1
3680 .IP \(bu 2.3
3681 .\}
3682 Java heap
3683 .RE
3684 .sp
3685 .RS 4
3686 .ie n \{\
3687 \h'-04'\(bu\h'+03'\c
3688 .\}
3689 .el \{\
3690 .sp -1
3691 .IP \(bu 2.3
3692 .\}
3693 Code cache
3694 .RE
3695 .sp
3696 .RS 4
3697 .ie n \{\
3698 \h'-04'\(bu\h'+03'\c
3699 .\}
3700 .el \{\
3701 .sp -1
3702 .IP \(bu 2.3
3703 .\}
3704 The marking bitmap data structure for the parallel GC
3705 .RE
3706 .sp
3707 Consequently, if you configure the
3708 \fBnr_hugepages\fR
3709 parameter to the size of the Java heap, then the JVM can fail in allocating the code cache areas on large pages because these areas are quite large in size\&.
3710 .RE
3711 T}
3712 .TE
3713 .sp 1
3714 .sp .5v
3715 .RE
3716 .RE
3717 .SH "EXIT STATUS"
3718 .PP
3719 The following exit values are typically returned by the launcher when the launcher is called with the wrong arguments, serious errors, or exceptions thrown by the JVM\&. However, a Java application may choose to return any value by using the API call
3720 \fBSystem\&.exit(exitValue)\fR\&. The values are:
3721 .sp
3722 .RS 4
3723 .ie n \{\
3724 \h'-04'\(bu\h'+03'\c
3725 .\}
3726 .el \{\
3727 .sp -1
3728 .IP \(bu 2.3
3729 .\}
3730 \fB0\fR: Successful completion
3731 .RE
3732 .sp
3733 .RS 4
3734 .ie n \{\
3735 \h'-04'\(bu\h'+03'\c
3736 .\}
3737 .el \{\
3738 .sp -1
3739 .IP \(bu 2.3
3740 .\}
3741 \fB>0\fR: An error occurred
3742 .RE
3743 .SH "SEE ALSO"
3744 .sp
3745 .RS 4
3746 .ie n \{\
3747 \h'-04'\(bu\h'+03'\c
3748 .\}
3749 .el \{\
3750 .sp -1
3751 .IP \(bu 2.3
3752 .\}
3753 javac(1)
3754 .RE
3755 .sp
3756 .RS 4
3757 .ie n \{\
3758 \h'-04'\(bu\h'+03'\c
3759 .\}
3760 .el \{\
3761 .sp -1
3762 .IP \(bu 2.3
3763 .\}
3764 jdb(1)
3765 .RE
3766 .sp
3767 .RS 4
3768 .ie n \{\
3769 \h'-04'\(bu\h'+03'\c
3770 .\}
3771 .el \{\
3772 .sp -1
3773 .IP \(bu 2.3
3774 .\}
3775 javah(1)
3776 .RE
3777 .sp
3778 .RS 4
3779 .ie n \{\
3780 \h'-04'\(bu\h'+03'\c
3781 .\}
3782 .el \{\
3783 .sp -1
3784 .IP \(bu 2.3
3785 .\}
3786 jar(1)
3787 .RE
3788 .sp
3789 .RS 4
3790 .ie n \{\
3791 \h'-04'\(bu\h'+03'\c
3792 .\}
3793 .el \{\
3794 .sp -1
3795 .IP \(bu 2.3
3796 .\}
3797 jstat(1)
3798 .RE
3799 .br
3800 'pl 8.5i
3801 'bp