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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 \-Xrs
925 .RS 4
926 Reduces the use of operating system signals by the JVM\&.
927 .sp
928 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\&.
929 .sp
930 The JVM catches signals to implement shutdown hooks for unexpected termination\&. The JVM uses
931 \fBSIGHUP\fR,
932 \fBSIGINT\fR, and
933 \fBSIGTERM\fR
934 to initiate the running of shutdown hooks\&.
935 .sp
936 The JVM uses a similar mechanism to implement the feature of dumping thread stacks for debugging purposes\&. The JVM uses
937 \fBSIGQUIT\fR
938 to perform thread dumps\&.
939 .sp
940 Applications embedding the JVM frequently need to trap signals such as
941 \fBSIGINT\fR
942 or
943 \fBSIGTERM\fR, which can lead to interference with the JVM signal handlers\&. The
944 \fB\-Xrs\fR
945 option is available to address this issue\&. When
946 \fB\-Xrs\fR
947 is used, the signal masks for
948 \fBSIGINT\fR,
949 \fBSIGTERM\fR,
950 \fBSIGHUP\fR, and
951 \fBSIGQUIT\fR
952 are not changed by the JVM, and signal handlers for these signals are not installed\&.
953 .sp
954 There are two consequences of specifying
955 \fB\-Xrs\fR:
956 .sp
957 .RS 4
958 .ie n \{\
959 \h'-04'\(bu\h'+03'\c
960 .\}
961 .el \{\
962 .sp -1
963 .IP \(bu 2.3
964 .\}
965 \fBSIGQUIT\fR
966 thread dumps are not available\&.
967 .RE
968 .sp
969 .RS 4
970 .ie n \{\
971 \h'-04'\(bu\h'+03'\c
972 .\}
973 .el \{\
974 .sp -1
975 .IP \(bu 2.3
976 .\}
977 User code is responsible for causing shutdown hooks to run, for example, by calling
978 \fBSystem\&.exit()\fR
979 when the JVM is to be terminated\&.
980 .RE
981 .RE
982 .PP
983 \-Xshare:\fImode\fR
984 .RS 4
985 Sets the class data sharing (CDS) mode\&. Possible
986 \fImode\fR
987 arguments for this option include the following:
988 .PP
989 auto
990 .RS 4
991 Use CDS if possible\&. This is the default value for Java HotSpot 32\-Bit Client VM\&.
992 .RE
993 .PP
994 on
995 .RS 4
996 Require the use of CDS\&. Print an error message and exit if class data sharing cannot be used\&.
997 .RE
998 .PP
999 off
1000 .RS 4
1001 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\&.
1002 .RE
1003 .PP
1004 dump
1005 .RS 4
1006 Manually generate the CDS archive\&. Specify the application class path as described in "Setting the Class Path "\&.
1007 .sp
1008 You should regenerate the CDS archive with each new JDK release\&.
1009 .RE
1010 .RE
1011 .PP
1012 \-XshowSettings:\fIcategory\fR
1013 .RS 4
1014 Shows settings and continues\&. Possible
1015 \fIcategory\fR
1016 arguments for this option include the following:
1017 .PP
1018 all
1019 .RS 4
1020 Shows all categories of settings\&. This is the default value\&.
1021 .RE
1022 .PP
1023 locale
1024 .RS 4
1025 Shows settings related to locale\&.
1026 .RE
1027 .PP
1028 properties
1029 .RS 4
1030 Shows settings related to system properties\&.
1031 .RE
1032 .PP
1033 vm
1034 .RS 4
1035 Shows the settings of the JVM\&.
1036 .RE
1037 .RE
1038 .PP
1039 \-Xss\fIsize\fR
1040 .RS 4
1041 Sets the thread stack size (in bytes)\&. Append the letter
1042 \fBk\fR
1043 or
1044 \fBK\fR
1045 to indicate KB,
1046 \fBm\fR
1047 or
1048 \fBM\fR
1049 to indicate MB,
1050 \fBg\fR
1051 or
1052 \fBG\fR
1053 to indicate GB\&. The default value depends on the platform:
1054 .sp
1055 .RS 4
1056 .ie n \{\
1057 \h'-04'\(bu\h'+03'\c
1058 .\}
1059 .el \{\
1060 .sp -1
1061 .IP \(bu 2.3
1062 .\}
1063 Linux/ARM (32\-bit): 320 KB
1064 .RE
1065 .sp
1066 .RS 4
1067 .ie n \{\
1068 \h'-04'\(bu\h'+03'\c
1069 .\}
1070 .el \{\
1071 .sp -1
1072 .IP \(bu 2.3
1073 .\}
1074 Linux/i386 (32\-bit): 320 KB
1075 .RE
1076 .sp
1077 .RS 4
1078 .ie n \{\
1079 \h'-04'\(bu\h'+03'\c
1080 .\}
1081 .el \{\
1082 .sp -1
1083 .IP \(bu 2.3
1084 .\}
1085 Linux/x64 (64\-bit): 1024 KB
1086 .RE
1087 .sp
1088 .RS 4
1089 .ie n \{\
1090 \h'-04'\(bu\h'+03'\c
1091 .\}
1092 .el \{\
1093 .sp -1
1094 .IP \(bu 2.3
1095 .\}
1096 OS X (64\-bit): 1024 KB
1097 .RE
1098 .sp
1099 .RS 4
1100 .ie n \{\
1101 \h'-04'\(bu\h'+03'\c
1102 .\}
1103 .el \{\
1104 .sp -1
1105 .IP \(bu 2.3
1106 .\}
1107 Oracle Solaris/i386 (32\-bit): 320 KB
1108 .RE
1109 .sp
1110 .RS 4
1111 .ie n \{\
1112 \h'-04'\(bu\h'+03'\c
1113 .\}
1114 .el \{\
1115 .sp -1
1116 .IP \(bu 2.3
1117 .\}
1118 Oracle Solaris/x64 (64\-bit): 1024 KB
1119 .RE
1120 .sp
1121 The following examples set the thread stack size to 1024 KB in different units:
1122 .sp
1123 .if n \{\
1124 .RS 4
1125 .\}
1126 .nf
1127 \fB\-Xss1m\fR
1128 \fB\-Xss1024k\fR
1129 \fB\-Xss1048576\fR
1130
1131 .fi
1132 .if n \{\
1133 .RE
1134 .\}
1135 This option is equivalent to
1136 \fB\-XX:ThreadStackSize\fR\&.
1137 .RE
1138 .PP
1139 \-Xusealtsigs
1140 .RS 4
1141 Use alternative signals instead of
1142 \fBSIGUSR1\fR
1143 and
1144 \fBSIGUSR2\fR
1145 for JVM internal signals\&. This option is equivalent to
1146 \fB\-XX:+UseAltSigs\fR\&.
1147 .RE
1148 .PP
1149 \-Xverify:\fImode\fR
1150 .RS 4
1151 Sets the mode of the bytecode verifier\&. Bytecode verification helps to troubleshoot some problems, but it also adds overhead to the running application\&. Possible
1152 \fImode\fR
1153 arguments for this option include the following:
1154 .PP
1155 none
1156 .RS 4
1157 Do not verify the bytecode\&. This reduces startup time and also reduces the protection provided by Java\&.
1158 .RE
1159 .PP
1160 remote
1161 .RS 4
1162 Verify those classes that are not loaded by the bootstrap class loader\&. This is the default behavior if you do not specify the
1163 \fB\-Xverify\fR
1164 option\&.
1165 .RE
1166 .PP
1167 all
1168 .RS 4
1169 Verify all classes\&.
1170 .RE
1171 .RE
1172 .SS "Advanced Runtime Options"
1173 .PP
1174 These options control the runtime behavior of the Java HotSpot VM\&.
1175 .PP
1176 \-XX:+CheckEndorsedAndExtDirs
1177 .RS 4
1178 Enables the option to prevent the
1179 \fBjava\fR
1180 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:
1181 .sp
1182 .RS 4
1183 .ie n \{\
1184 \h'-04'\(bu\h'+03'\c
1185 .\}
1186 .el \{\
1187 .sp -1
1188 .IP \(bu 2.3
1189 .\}
1190 The
1191 \fBjava\&.ext\&.dirs\fR
1192 or
1193 \fBjava\&.endorsed\&.dirs\fR
1194 system property is set\&.
1195 .RE
1196 .sp
1197 .RS 4
1198 .ie n \{\
1199 \h'-04'\(bu\h'+03'\c
1200 .\}
1201 .el \{\
1202 .sp -1
1203 .IP \(bu 2.3
1204 .\}
1205 The
1206 \fBlib/endorsed\fR
1207 directory exists and is not empty\&.
1208 .RE
1209 .sp
1210 .RS 4
1211 .ie n \{\
1212 \h'-04'\(bu\h'+03'\c
1213 .\}
1214 .el \{\
1215 .sp -1
1216 .IP \(bu 2.3
1217 .\}
1218 The
1219 \fBlib/ext\fR
1220 directory contains any JAR files other than those of the JDK\&.
1221 .RE
1222 .sp
1223 .RS 4
1224 .ie n \{\
1225 \h'-04'\(bu\h'+03'\c
1226 .\}
1227 .el \{\
1228 .sp -1
1229 .IP \(bu 2.3
1230 .\}
1231 The system\-wide platform\-specific extension directory contains any JAR files\&.
1232 .RE
1233 .RE
1234 .PP
1235 \-XX:+DisableAttachMechanism
1236 .RS 4
1237 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
1238 \fBjcmd\fR,
1239 \fBjstack\fR,
1240 \fBjmap\fR, and
1241 \fBjinfo\fR\&.
1242 .RE
1243 .PP
1244 \-XX:ErrorFile=\fIfilename\fR
1245 .RS 4
1246 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
1247 \fBhs_err_pid\fR\fIpid\fR\fB\&.log\fR
1248 where
1249 \fIpid\fR
1250 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
1251 \fB%p\fR):
1252 .sp
1253 .if n \{\
1254 .RS 4
1255 .\}
1256 .nf
1257 \fB\-XX:ErrorFile=\&./hs_err_pid%p\&.log\fR
1258
1259 .fi
1260 .if n \{\
1261 .RE
1262 .\}
1263 The following example shows how to set the error log to
1264 \fB/var/log/java/java_error\&.log\fR:
1265 .sp
1266 .if n \{\
1267 .RS 4
1268 .\}
1269 .nf
1270 \fB\-XX:ErrorFile=/var/log/java/java_error\&.log\fR
1271
1272 .fi
1273 .if n \{\
1274 .RE
1275 .\}
1276 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
1277 \fB/tmp\fR\&.
1278 .RE
1279 .PP
1280 \-XX:+FailOverToOldVerifier
1281 .RS 4
1282 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\&.
1283 .RE
1284 .PP
1285 \-XX:LargePageSizeInBytes=\fIsize\fR
1286 .RS 4
1287 On Solaris, sets the maximum size (in bytes) for large pages used for Java heap\&. The
1288 \fIsize\fR
1289 argument must be a power of 2 (2, 4, 8, 16, \&.\&.\&.)\&. Append the letter
1290 \fBk\fR
1291 or
1292 \fBK\fR
1293 to indicate kilobytes,
1294 \fBm\fR
1295 or
1296 \fBM\fR
1297 to indicate megabytes,
1298 \fBg\fR
1299 or
1300 \fBG\fR
1301 to indicate gigabytes\&. By default, the size is set to 0, meaning that the JVM chooses the size for large pages automatically\&.
1302 .sp
1303 The following example illustrates how to set the large page size to 4 megabytes (MB):
1304 .sp
1305 .if n \{\
1306 .RS 4
1307 .\}
1308 .nf
1309 \fB\-XX:LargePageSizeInBytes=4m\fR
1310
1311 .fi
1312 .if n \{\
1313 .RE
1314 .\}
1315 .RE
1316 .PP
1317 \-XX:MaxDirectMemorySize=\fIsize\fR
1318 .RS 4
1319 Sets the maximum total size (in bytes) of the New I/O (the
1320 \fBjava\&.nio\fR
1321 package) direct\-buffer allocations\&. Append the letter
1322 \fBk\fR
1323 or
1324 \fBK\fR
1325 to indicate kilobytes,
1326 \fBm\fR
1327 or
1328 \fBM\fR
1329 to indicate megabytes,
1330 \fBg\fR
1331 or
1332 \fBG\fR
1333 to indicate gigabytes\&. By default, the size is set to 0, meaning that the JVM chooses the size for NIO direct\-buffer allocations automatically\&.
1334 .sp
1335 The following examples illustrate how to set the NIO size to 1024 KB in different units:
1336 .sp
1337 .if n \{\
1338 .RS 4
1339 .\}
1340 .nf
1341 \fB\-XX:MaxDirectMemorySize=1m\fR
1342 \fB\-XX:MaxDirectMemorySize=1024k\fR
1343 \fB\-XX:MaxDirectMemorySize=1048576\fR
1344
1345 .fi
1346 .if n \{\
1347 .RE
1348 .\}
1349 .RE
1350 .PP
1351 \-XX:NativeMemoryTracking=\fImode\fR
1352 .RS 4
1353 Specifies the mode for tracking JVM native memory usage\&. Possible
1354 \fImode\fR
1355 arguments for this option include the following:
1356 .PP
1357 off
1358 .RS 4
1359 Do not track JVM native memory usage\&. This is the default behavior if you do not specify the
1360 \fB\-XX:NativeMemoryTracking\fR
1361 option\&.
1362 .RE
1363 .PP
1364 summary
1365 .RS 4
1366 Only track memory usage by JVM subsystems, such as Java heap, class, code, and thread\&.
1367 .RE
1368 .PP
1369 detail
1370 .RS 4
1371 In addition to tracking memory usage by JVM subsystems, track memory usage by individual
1372 \fBCallSite\fR, individual virtual memory region and its committed regions\&.
1373 .RE
1374 .RE
1375 .PP
1376 \-XX:ObjectAlignmentInBytes=\fIalignment\fR
1377 .RS 4
1378 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\&.
1379 .sp
1380 The heap size limit in bytes is calculated as:
1381 .sp
1382 \fB4GB * ObjectAlignmentInBytes\fR
1383 .sp
1384 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\&.
1385 .RE
1386 .PP
1387 \-XX:OnError=\fIstring\fR
1388 .RS 4
1389 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\&.
1390 .sp
1391 The following example shows how the
1392 \fB\-XX:OnError\fR
1393 option can be used to run the
1394 \fBgcore\fR
1395 command to create the core image, and the debugger is started to attach to the process in case of an irrecoverable error (the
1396 \fB%p\fR
1397 designates the current process):
1398 .sp
1399 .if n \{\
1400 .RS 4
1401 .\}
1402 .nf
1403 \fB\-XX:OnError="gcore %p;dbx \- %p"\fR
1404
1405 .fi
1406 .if n \{\
1407 .RE
1408 .\}
1409 .RE
1410 .PP
1411 \-XX:OnOutOfMemoryError=\fIstring\fR
1412 .RS 4
1413 Sets a custom command or a series of semicolon\-separated commands to run when an
1414 \fBOutOfMemoryError\fR
1415 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
1416 \fB\-XX:OnError\fR
1417 option\&.
1418 .RE
1419 .PP
1420 \-XX:+PerfDataSaveToFile
1421 .RS 4
1422 If enabled, saves
1423 jstat(1) binary data when the Java application exits\&. This binary data is saved in a file named
1424 \fBhsperfdata_\fR\fI<pid>\fR, where
1425 \fI<pid>\fR
1426 is the process identifier of the Java application you ran\&. Use
1427 \fBjstat\fR
1428 to display the performance data contained in this file as follows:
1429 .sp
1430 .if n \{\
1431 .RS 4
1432 .\}
1433 .nf
1434 \fBjstat \-class file:///\fR\fB\fI<path>\fR\fR\fB/hsperfdata_\fR\fB\fI<pid>\fR\fR
1435 \fBjstat \-gc file:///\fR\fB\fI<path>\fR\fR\fB/hsperfdata_\fR\fB\fI<pid>\fR\fR
1436 .fi
1437 .if n \{\
1438 .RE
1439 .\}
1440 .RE
1441 .PP
1442 \-XX:+PrintCommandLineFlags
1443 .RS 4
1444 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\&.
1445 .RE
1446 .PP
1447 \-XX:+PrintNMTStatistics
1448 .RS 4
1449 Enables printing of collected native memory tracking data at JVM exit when native memory tracking is enabled (see
1450 \fB\-XX:NativeMemoryTracking\fR)\&. By default, this option is disabled and native memory tracking data is not printed\&.
1451 .RE
1452 .PP
1453 \-XX:+RelaxAccessControlCheck
1454 .RS 4
1455 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\&.
1456 .RE
1457 .PP
1458 \-XX:+ShowMessageBoxOnError
1459 .RS 4
1460 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\&.
1461 .RE
1462 .PP
1463 \-XX:ThreadStackSize=\fIsize\fR
1464 .RS 4
1465 Sets the thread stack size (in bytes)\&. Append the letter
1466 \fBk\fR
1467 or
1468 \fBK\fR
1469 to indicate kilobytes,
1470 \fBm\fR
1471 or
1472 \fBM\fR
1473 to indicate megabytes,
1474 \fBg\fR
1475 or
1476 \fBG\fR
1477 to indicate gigabytes\&. The default value depends on the platform:
1478 .sp
1479 .RS 4
1480 .ie n \{\
1481 \h'-04'\(bu\h'+03'\c
1482 .\}
1483 .el \{\
1484 .sp -1
1485 .IP \(bu 2.3
1486 .\}
1487 Linux/ARM (32\-bit): 320 KB
1488 .RE
1489 .sp
1490 .RS 4
1491 .ie n \{\
1492 \h'-04'\(bu\h'+03'\c
1493 .\}
1494 .el \{\
1495 .sp -1
1496 .IP \(bu 2.3
1497 .\}
1498 Linux/i386 (32\-bit): 320 KB
1499 .RE
1500 .sp
1501 .RS 4
1502 .ie n \{\
1503 \h'-04'\(bu\h'+03'\c
1504 .\}
1505 .el \{\
1506 .sp -1
1507 .IP \(bu 2.3
1508 .\}
1509 Linux/x64 (64\-bit): 1024 KB
1510 .RE
1511 .sp
1512 .RS 4
1513 .ie n \{\
1514 \h'-04'\(bu\h'+03'\c
1515 .\}
1516 .el \{\
1517 .sp -1
1518 .IP \(bu 2.3
1519 .\}
1520 OS X (64\-bit): 1024 KB
1521 .RE
1522 .sp
1523 .RS 4
1524 .ie n \{\
1525 \h'-04'\(bu\h'+03'\c
1526 .\}
1527 .el \{\
1528 .sp -1
1529 .IP \(bu 2.3
1530 .\}
1531 Oracle Solaris/i386 (32\-bit): 320 KB
1532 .RE
1533 .sp
1534 .RS 4
1535 .ie n \{\
1536 \h'-04'\(bu\h'+03'\c
1537 .\}
1538 .el \{\
1539 .sp -1
1540 .IP \(bu 2.3
1541 .\}
1542 Oracle Solaris/x64 (64\-bit): 1024 KB
1543 .RE
1544 .sp
1545 The following examples show how to set the thread stack size to 1024 KB in different units:
1546 .sp
1547 .if n \{\
1548 .RS 4
1549 .\}
1550 .nf
1551 \fB\-XX:ThreadStackSize=1m\fR
1552 \fB\-XX:ThreadStackSize=1024k\fR
1553 \fB\-XX:ThreadStackSize=1048576\fR
1554
1555 .fi
1556 .if n \{\
1557 .RE
1558 .\}
1559 This option is equivalent to
1560 \fB\-Xss\fR\&.
1561 .RE
1562 .PP
1563 \-XX:+TraceClassLoading
1564 .RS 4
1565 Enables tracing of classes as they are loaded\&. By default, this option is disabled and classes are not traced\&.
1566 .RE
1567 .PP
1568 \-XX:+TraceClassLoadingPreorder
1569 .RS 4
1570 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\&.
1571 .RE
1572 .PP
1573 \-XX:+TraceClassResolution
1574 .RS 4
1575 Enables tracing of constant pool resolutions\&. By default, this option is disabled and constant pool resolutions are not traced\&.
1576 .RE
1577 .PP
1578 \-XX:+TraceClassUnloading
1579 .RS 4
1580 Enables tracing of classes as they are unloaded\&. By default, this option is disabled and classes are not traced\&.
1581 .RE
1582 .PP
1583 \-XX:+TraceLoaderConstraints
1584 .RS 4
1585 Enables tracing of the loader constraints recording\&. By default, this option is disabled and loader constraints recording is not traced\&.
1586 .RE
1587 .PP
1588 \-XX:+UseAltSigs
1589 .RS 4
1590 Enables the use of alternative signals instead of
1591 \fBSIGUSR1\fR
1592 and
1593 \fBSIGUSR2\fR
1594 for JVM internal signals\&. By default, this option is disabled and alternative signals are not used\&. This option is equivalent to
1595 \fB\-Xusealtsigs\fR\&.
1596 .RE
1597 .PP
1598 \-XX:\-UseBiasedLocking
1599 .RS 4
1600 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
1601 .sp
1602 By default, this option is enabled\&.
1603 .RE
1604 .PP
1605 \-XX:\-UseCompressedOops
1606 .RS 4
1607 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\&.
1608 .sp
1609 It is also possible to use compressed pointers when Java heap sizes are greater than 32GB\&. See the
1610 \fB\-XX:ObjectAlignmentInBytes\fR
1611 option\&.
1612 .RE
1613 .PP
1614 \-XX:+UseHugeTLBFS
1615 .RS 4
1616 This option for Linux is the equivalent of specifying
1617 \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
1618 \fB\-XX:UseTransparentHugePages\fR
1619 if you want this behavior\&.
1620 .sp
1621 For more information, see "Large Pages"\&.
1622 .RE
1623 .PP
1624 \-XX:+UseLargePages
1625 .RS 4
1626 Enables the use of large page memory\&. By default, this option is disabled and large page memory is not used\&.
1627 .sp
1628 For more information, see "Large Pages"\&.
1629 .RE
1630 .PP
1631 \-XX:+UseMembar
1632 .RS 4
1633 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\&.)
1634 .RE
1635 .PP
1636 \-XX:+UsePerfData
1637 .RS 4
1638 Enables the
1639 \fBperfdata\fR
1640 feature\&. This option is enabled by default to allow JVM monitoring and performance testing\&. Disabling it suppresses the creation of the
1641 \fBhsperfdata_userid\fR
1642 directories\&. To disable the
1643 \fBperfdata\fR
1644 feature, specify
1645 \fB\-XX:\-UsePerfData\fR\&.
1646 .RE
1647 .PP
1648 \-XX:+UseTransparentHugePages
1649 .RS 4
1650 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\&.
1651 .sp
1652 For more information, see "Large Pages"\&.
1653 .RE
1654 .PP
1655 \-XX:+AllowUserSignalHandlers
1656 .RS 4
1657 Enables installation of signal handlers by the application\&. By default, this option is disabled and the application is not allowed to install signal handlers\&.
1658 .RE
1659 .SS "Advanced JIT Compiler Options"
1660 .PP
1661 These options control the dynamic just\-in\-time (JIT) compilation performed by the Java HotSpot VM\&.
1662 .PP
1663 \-XX:+AggressiveOpts
1664 .RS 4
1665 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\&.
1666 .RE
1667 .PP
1668 \-XX:AllocateInstancePrefetchLines=\fIlines\fR
1669 .RS 4
1670 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:
1671 .sp
1672 .if n \{\
1673 .RS 4
1674 .\}
1675 .nf
1676 \fB\-XX:AllocateInstancePrefetchLines=1\fR
1677
1678 .fi
1679 .if n \{\
1680 .RE
1681 .\}
1682 Only the Java HotSpot Server VM supports this option\&.
1683 .RE
1684 .PP
1685 \-XX:AllocatePrefetchDistance=\fIsize\fR
1686 .RS 4
1687 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\&.
1688 .sp
1689 Negative values denote that prefetch distance is chosen based on the platform\&. Positive values are bytes to prefetch\&. Append the letter
1690 \fBk\fR
1691 or
1692 \fBK\fR
1693 to indicate kilobytes,
1694 \fBm\fR
1695 or
1696 \fBM\fR
1697 to indicate megabytes,
1698 \fBg\fR
1699 or
1700 \fBG\fR
1701 to indicate gigabytes\&. The default value is set to \-1\&.
1702 .sp
1703 The following example shows how to set the prefetch distance to 1024 bytes:
1704 .sp
1705 .if n \{\
1706 .RS 4
1707 .\}
1708 .nf
1709 \fB\-XX:AllocatePrefetchDistance=1024\fR
1710
1711 .fi
1712 .if n \{\
1713 .RE
1714 .\}
1715 Only the Java HotSpot Server VM supports this option\&.
1716 .RE
1717 .PP
1718 \-XX:AllocatePrefetchInstr=\fIinstruction\fR
1719 .RS 4
1720 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:
1721 .sp
1722 .if n \{\
1723 .RS 4
1724 .\}
1725 .nf
1726 \fB\-XX:AllocatePrefetchInstr=0\fR
1727
1728 .fi
1729 .if n \{\
1730 .RE
1731 .\}
1732 Only the Java HotSpot Server VM supports this option\&.
1733 .RE
1734 .PP
1735 \-XX:AllocatePrefetchLines=\fIlines\fR
1736 .RS 4
1737 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\&.
1738 .sp
1739 The following example shows how to set the number of loaded cache lines to 5:
1740 .sp
1741 .if n \{\
1742 .RS 4
1743 .\}
1744 .nf
1745 \fB\-XX:AllocatePrefetchLines=5\fR
1746
1747 .fi
1748 .if n \{\
1749 .RE
1750 .\}
1751 Only the Java HotSpot Server VM supports this option\&.
1752 .RE
1753 .PP
1754 \-XX:AllocatePrefetchStepSize=\fIsize\fR
1755 .RS 4
1756 Sets the step size (in bytes) for sequential prefetch instructions\&. Append the letter
1757 \fBk\fR
1758 or
1759 \fBK\fR
1760 to indicate kilobytes,
1761 \fBm\fR
1762 or
1763 \fBM\fR
1764 to indicate megabytes,
1765 \fBg\fR
1766 or
1767 \fBG\fR
1768 to indicate gigabytes\&. By default, the step size is set to 16 bytes:
1769 .sp
1770 .if n \{\
1771 .RS 4
1772 .\}
1773 .nf
1774 \fB\-XX:AllocatePrefetchStepSize=16\fR
1775
1776 .fi
1777 .if n \{\
1778 .RE
1779 .\}
1780 Only the Java HotSpot Server VM supports this option\&.
1781 .RE
1782 .PP
1783 \-XX:AllocatePrefetchStyle=\fIstyle\fR
1784 .RS 4
1785 Sets the generated code style for prefetch instructions\&. The
1786 \fIstyle\fR
1787 argument is an integer from 0 to 3:
1788 .PP
1789 0
1790 .RS 4
1791 Do not generate prefetch instructions\&.
1792 .RE
1793 .PP
1794 1
1795 .RS 4
1796 Execute prefetch instructions after each allocation\&. This is the default parameter\&.
1797 .RE
1798 .PP
1799 2
1800 .RS 4
1801 Use the thread\-local allocation block (TLAB) watermark pointer to determine when prefetch instructions are executed\&.
1802 .RE
1803 .PP
1804 3
1805 .RS 4
1806 Use BIS instruction on SPARC for allocation prefetch\&.
1807 .RE
1808 .sp
1809 Only the Java HotSpot Server VM supports this option\&.
1810 .RE
1811 .PP
1812 \-XX:+BackgroundCompilation
1813 .RS 4
1814 Enables background compilation\&. This option is enabled by default\&. To disable background compilation, specify
1815 \fB\-XX:\-BackgroundCompilation\fR
1816 (this is equivalent to specifying
1817 \fB\-Xbatch\fR)\&.
1818 .RE
1819 .PP
1820 \-XX:CICompilerCount=\fIthreads\fR
1821 .RS 4
1822 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:
1823 .sp
1824 .if n \{\
1825 .RS 4
1826 .\}
1827 .nf
1828 \fB\-XX:CICompilerCount=2\fR
1829
1830 .fi
1831 .if n \{\
1832 .RE
1833 .\}
1834 .RE
1835 .PP
1836 \-XX:CodeCacheMinimumFreeSpace=\fIsize\fR
1837 .RS 4
1838 Sets the minimum free space (in bytes) required for compilation\&. Append the letter
1839 \fBk\fR
1840 or
1841 \fBK\fR
1842 to indicate kilobytes,
1843 \fBm\fR
1844 or
1845 \fBM\fR
1846 to indicate megabytes,
1847 \fBg\fR
1848 or
1849 \fBG\fR
1850 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:
1851 .sp
1852 .if n \{\
1853 .RS 4
1854 .\}
1855 .nf
1856 \fB\-XX:CodeCacheMinimumFreeSpace=1024m\fR
1857
1858 .fi
1859 .if n \{\
1860 .RE
1861 .\}
1862 .RE
1863 .PP
1864 \-XX:CompileCommand=\fIcommand\fR,\fImethod\fR[,\fIoption\fR]
1865 .RS 4
1866 Specifies a command to perform on a method\&. For example, to exclude the
1867 \fBindexOf()\fR
1868 method of the
1869 \fBString\fR
1870 class from being compiled, use the following:
1871 .sp
1872 .if n \{\
1873 .RS 4
1874 .\}
1875 .nf
1876 \fB\-XX:CompileCommand=exclude,java/lang/String\&.indexOf\fR
1877
1878 .fi
1879 .if n \{\
1880 .RE
1881 .\}
1882 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
1883 \fB\-XX:+PrintCompilation\fR
1884 and
1885 \fB\-XX:+LogCompilation\fR
1886 options:
1887 .sp
1888 .if n \{\
1889 .RS 4
1890 .\}
1891 .nf
1892 \fB\-XX:CompileCommand=exclude,java\&.lang\&.String::indexOf\fR
1893
1894 .fi
1895 .if n \{\
1896 .RE
1897 .\}
1898 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
1899 \fBindexOf(String)\fR
1900 method of the
1901 \fBString\fR
1902 class from being compiled, use the following:
1903 .sp
1904 .if n \{\
1905 .RS 4
1906 .\}
1907 .nf
1908 \fB\-XX:CompileCommand="exclude,java/lang/String\&.indexOf,(Ljava/lang/String;)I"\fR
1909
1910 .fi
1911 .if n \{\
1912 .RE
1913 .\}
1914 You can also use the asterisk (*) as a wildcard for class and method names\&. For example, to exclude all
1915 \fBindexOf()\fR
1916 methods in all classes from being compiled, use the following:
1917 .sp
1918 .if n \{\
1919 .RS 4
1920 .\}
1921 .nf
1922 \fB\-XX:CompileCommand=exclude,*\&.indexOf\fR
1923
1924 .fi
1925 .if n \{\
1926 .RE
1927 .\}
1928 The commas and periods are aliases for spaces, making it easier to pass compiler commands through a shell\&. You can pass arguments to
1929 \fB\-XX:CompileCommand\fR
1930 using spaces as separators by enclosing the argument in quotation marks:
1931 .sp
1932 .if n \{\
1933 .RS 4
1934 .\}
1935 .nf
1936 \fB\-XX:CompileCommand="exclude java/lang/String indexOf"\fR
1937
1938 .fi
1939 .if n \{\
1940 .RE
1941 .\}
1942 Note that after parsing the commands passed on the command line using the
1943 \fB\-XX:CompileCommand\fR
1944 options, the JIT compiler then reads commands from the
1945 \fB\&.hotspot_compiler\fR
1946 file\&. You can add commands to this file or specify a different file using the
1947 \fB\-XX:CompileCommandFile\fR
1948 option\&.
1949 .sp
1950 To add several commands, either specify the
1951 \fB\-XX:CompileCommand\fR
1952 option multiple times, or separate each argument with the newline separator (\fB\en\fR)\&. The following commands are available:
1953 .PP
1954 break
1955 .RS 4
1956 Set a breakpoint when debugging the JVM to stop at the beginning of compilation of the specified method\&.
1957 .RE
1958 .PP
1959 compileonly
1960 .RS 4
1961 Exclude all methods from compilation except for the specified method\&. As an alternative, you can use the
1962 \fB\-XX:CompileOnly\fR
1963 option, which allows to specify several methods\&.
1964 .RE
1965 .PP
1966 dontinline
1967 .RS 4
1968 Prevent inlining of the specified method\&.
1969 .RE
1970 .PP
1971 exclude
1972 .RS 4
1973 Exclude the specified method from compilation\&.
1974 .RE
1975 .PP
1976 help
1977 .RS 4
1978 Print a help message for the
1979 \fB\-XX:CompileCommand\fR
1980 option\&.
1981 .RE
1982 .PP
1983 inline
1984 .RS 4
1985 Attempt to inline the specified method\&.
1986 .RE
1987 .PP
1988 log
1989 .RS 4
1990 Exclude compilation logging (with the
1991 \fB\-XX:+LogCompilation\fR
1992 option) for all methods except for the specified method\&. By default, logging is performed for all compiled methods\&.
1993 .RE
1994 .PP
1995 option
1996 .RS 4
1997 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
1998 \fBBlockLayoutByFrequency\fR
1999 option for the
2000 \fBappend()\fR
2001 method of the
2002 \fBStringBuffer\fR
2003 class, use the following:
2004 .sp
2005 .if n \{\
2006 .RS 4
2007 .\}
2008 .nf
2009 \fB\-XX:CompileCommand=option,java/lang/StringBuffer\&.append,BlockLayoutByFrequency\fR
2010
2011 .fi
2012 .if n \{\
2013 .RE
2014 .\}
2015 You can specify multiple compilation options, separated by commas or spaces\&.
2016 .RE
2017 .PP
2018 print
2019 .RS 4
2020 Print generated assembler code after compilation of the specified method\&.
2021 .RE
2022 .PP
2023 quiet
2024 .RS 4
2025 Do not print the compile commands\&. By default, the commands that you specify with the \-\fBXX:CompileCommand\fR
2026 option are printed; for example, if you exclude from compilation the
2027 \fBindexOf()\fR
2028 method of the
2029 \fBString\fR
2030 class, then the following will be printed to standard output:
2031 .sp
2032 .if n \{\
2033 .RS 4
2034 .\}
2035 .nf
2036 \fBCompilerOracle: exclude java/lang/String\&.indexOf\fR
2037
2038 .fi
2039 .if n \{\
2040 .RE
2041 .\}
2042 You can suppress this by specifying the
2043 \fB\-XX:CompileCommand=quiet\fR
2044 option before other
2045 \fB\-XX:CompileCommand\fR
2046 options\&.
2047 .RE
2048 .RE
2049 .PP
2050 \-XX:CompileCommandFile=\fIfilename\fR
2051 .RS 4
2052 Sets the file from which JIT compiler commands are read\&. By default, the
2053 \fB\&.hotspot_compiler\fR
2054 file is used to store commands performed by the JIT compiler\&.
2055 .sp
2056 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
2057 \fBtoString()\fR
2058 method of the
2059 \fBString\fR
2060 class:
2061 .sp
2062 .if n \{\
2063 .RS 4
2064 .\}
2065 .nf
2066 \fBprint java/lang/String toString\fR
2067
2068 .fi
2069 .if n \{\
2070 .RE
2071 .\}
2072 For more information about specifying the commands for the JIT compiler to perform on methods, see the
2073 \fB\-XX:CompileCommand\fR
2074 option\&.
2075 .RE
2076 .PP
2077 \-XX:CompileOnly=\fImethods\fR
2078 .RS 4
2079 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
2080 \fBlength()\fR
2081 method of the
2082 \fBString\fR
2083 class and the
2084 \fBsize()\fR
2085 method of the
2086 \fBList\fR
2087 class, use the following:
2088 .sp
2089 .if n \{\
2090 .RS 4
2091 .\}
2092 .nf
2093 \fB\-XX:CompileOnly=java/lang/String\&.length,java/util/List\&.size\fR
2094
2095 .fi
2096 .if n \{\
2097 .RE
2098 .\}
2099 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
2100 \fB\-XX:+PrintCompilation\fR
2101 and
2102 \fB\-XX:+LogCompilation\fR
2103 options:
2104 .sp
2105 .if n \{\
2106 .RS 4
2107 .\}
2108 .nf
2109 \fB\-XX:CompileOnly=java\&.lang\&.String::length,java\&.util\&.List::size\fR
2110
2111 .fi
2112 .if n \{\
2113 .RE
2114 .\}
2115 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:
2116 .sp
2117 .if n \{\
2118 .RS 4
2119 .\}
2120 .nf
2121 \fB\-XX:CompileOnly=java/lang/String\fR
2122 \fB\-XX:CompileOnly=java/lang\fR
2123 \fB\-XX:CompileOnly=\&.length\fR
2124
2125 .fi
2126 .if n \{\
2127 .RE
2128 .\}
2129 .RE
2130 .PP
2131 \-XX:CompileThreshold=\fIinvocations\fR
2132 .RS 4
2133 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
2134 \fB\-XX:+TieredCompilation\fR\&. The following example shows how to set the number of interpreted method invocations to 5,000:
2135 .sp
2136 .if n \{\
2137 .RS 4
2138 .\}
2139 .nf
2140 \fB\-XX:CompileThreshold=5000\fR
2141
2142 .fi
2143 .if n \{\
2144 .RE
2145 .\}
2146 You can completely disable interpretation of Java methods before compilation by specifying the
2147 \fB\-Xcomp\fR
2148 option\&.
2149 .RE
2150 .PP
2151 \-XX:+DoEscapeAnalysis
2152 .RS 4
2153 Enables the use of escape analysis\&. This option is enabled by default\&. To disable the use of escape analysis, specify
2154 \fB\-XX:\-DoEscapeAnalysis\fR\&. Only the Java HotSpot Server VM supports this option\&.
2155 .RE
2156 .PP
2157 \-XX:InitialCodeCacheSize=\fIsize\fR
2158 .RS 4
2159 Sets the initial code cache size (in bytes)\&. Append the letter
2160 \fBk\fR
2161 or
2162 \fBK\fR
2163 to indicate kilobytes,
2164 \fBm\fR
2165 or
2166 \fBM\fR
2167 to indicate megabytes,
2168 \fBg\fR
2169 or
2170 \fBG\fR
2171 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:
2172 .sp
2173 .if n \{\
2174 .RS 4
2175 .\}
2176 .nf
2177 \fB\-XX:InitialCodeCacheSize=32k\fR
2178
2179 .fi
2180 .if n \{\
2181 .RE
2182 .\}
2183 .RE
2184 .PP
2185 \-XX:+Inline
2186 .RS 4
2187 Enables method inlining\&. This option is enabled by default to increase performance\&. To disable method inlining, specify
2188 \fB\-XX:\-Inline\fR\&.
2189 .RE
2190 .PP
2191 \-XX:InlineSmallCode=\fIsize\fR
2192 .RS 4
2193 Sets the maximum code size (in bytes) for compiled methods that should be inlined\&. Append the letter
2194 \fBk\fR
2195 or
2196 \fBK\fR
2197 to indicate kilobytes,
2198 \fBm\fR
2199 or
2200 \fBM\fR
2201 to indicate megabytes,
2202 \fBg\fR
2203 or
2204 \fBG\fR
2205 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:
2206 .sp
2207 .if n \{\
2208 .RS 4
2209 .\}
2210 .nf
2211 \fB\-XX:InlineSmallCode=1000\fR
2212
2213 .fi
2214 .if n \{\
2215 .RE
2216 .\}
2217 .RE
2218 .PP
2219 \-XX:+LogCompilation
2220 .RS 4
2221 Enables logging of compilation activity to a file named
2222 \fBhotspot\&.log\fR
2223 in the current working directory\&. You can specify a different log file path and name using the
2224 \fB\-XX:LogFile\fR
2225 option\&.
2226 .sp
2227 By default, this option is disabled and compilation activity is not logged\&. The
2228 \fB\-XX:+LogCompilation\fR
2229 option has to be used together with the
2230 \fB\-XX:UnlockDiagnosticVMOptions\fR
2231 option that unlocks diagnostic JVM options\&.
2232 .sp
2233 You can enable verbose diagnostic output with a message printed to the console every time a method is compiled by using the
2234 \fB\-XX:+PrintCompilation\fR
2235 option\&.
2236 .RE
2237 .PP
2238 \-XX:MaxInlineSize=\fIsize\fR
2239 .RS 4
2240 Sets the maximum bytecode size (in bytes) of a method to be inlined\&. Append the letter
2241 \fBk\fR
2242 or
2243 \fBK\fR
2244 to indicate kilobytes,
2245 \fBm\fR
2246 or
2247 \fBM\fR
2248 to indicate megabytes,
2249 \fBg\fR
2250 or
2251 \fBG\fR
2252 to indicate gigabytes\&. By default, the maximum bytecode size is set to 35 bytes:
2253 .sp
2254 .if n \{\
2255 .RS 4
2256 .\}
2257 .nf
2258 \fB\-XX:MaxInlineSize=35\fR
2259
2260 .fi
2261 .if n \{\
2262 .RE
2263 .\}
2264 .RE
2265 .PP
2266 \-XX:MaxNodeLimit=\fInodes\fR
2267 .RS 4
2268 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:
2269 .sp
2270 .if n \{\
2271 .RS 4
2272 .\}
2273 .nf
2274 \fB\-XX:MaxNodeLimit=65000\fR
2275
2276 .fi
2277 .if n \{\
2278 .RE
2279 .\}
2280 .RE
2281 .PP
2282 \-XX:MaxTrivialSize=\fIsize\fR
2283 .RS 4
2284 Sets the maximum bytecode size (in bytes) of a trivial method to be inlined\&. Append the letter
2285 \fBk\fR
2286 or
2287 \fBK\fR
2288 to indicate kilobytes,
2289 \fBm\fR
2290 or
2291 \fBM\fR
2292 to indicate megabytes,
2293 \fBg\fR
2294 or
2295 \fBG\fR
2296 to indicate gigabytes\&. By default, the maximum bytecode size of a trivial method is set to 6 bytes:
2297 .sp
2298 .if n \{\
2299 .RS 4
2300 .\}
2301 .nf
2302 \fB\-XX:MaxTrivialSize=6\fR
2303
2304 .fi
2305 .if n \{\
2306 .RE
2307 .\}
2308 .RE
2309 .PP
2310 \-XX:+OptimizeStringConcat
2311 .RS 4
2312 Enables the optimization of
2313 \fBString\fR
2314 concatenation operations\&. This option is enabled by default\&. To disable the optimization of
2315 \fBString\fR
2316 concatenation operations, specify
2317 \fB\-XX:\-OptimizeStringConcat\fR\&. Only the Java HotSpot Server VM supports this option\&.
2318 .RE
2319 .PP
2320 \-XX:+PrintAssembly
2321 .RS 4
2322 Enables printing of assembly code for bytecoded and native methods by using the external
2323 \fBdisassembler\&.so\fR
2324 library\&. This enables you to see the generated code, which may help you to diagnose performance issues\&.
2325 .sp
2326 By default, this option is disabled and assembly code is not printed\&. The
2327 \fB\-XX:+PrintAssembly\fR
2328 option has to be used together with the
2329 \fB\-XX:UnlockDiagnosticVMOptions\fR
2330 option that unlocks diagnostic JVM options\&.
2331 .RE
2332 .PP
2333 \-XX:+PrintCompilation
2334 .RS 4
2335 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\&.
2336 .sp
2337 You can also log compilation activity to a file by using the
2338 \fB\-XX:+LogCompilation\fR
2339 option\&.
2340 .RE
2341 .PP
2342 \-XX:+PrintInlining
2343 .RS 4
2344 Enables printing of inlining decisions\&. This enables you to see which methods are getting inlined\&.
2345 .sp
2346 By default, this option is disabled and inlining information is not printed\&. The
2347 \fB\-XX:+PrintInlining\fR
2348 option has to be used together with the
2349 \fB\-XX:+UnlockDiagnosticVMOptions\fR
2350 option that unlocks diagnostic JVM options\&.
2351 .RE
2352 .PP
2353 \-XX:ReservedCodeCacheSize=\fIsize\fR
2354 .RS 4
2355 Sets the maximum code cache size (in bytes) for JIT\-compiled code\&. Append the letter
2356 \fBk\fR
2357 or
2358 \fBK\fR
2359 to indicate kilobytes,
2360 \fBm\fR
2361 or
2362 \fBM\fR
2363 to indicate megabytes,
2364 \fBg\fR
2365 or
2366 \fBG\fR
2367 to indicate gigabytes\&. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option
2368 \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
2369 \fB\-XX:InitialCodeCacheSize\fR\&. This option is equivalent to
2370 \fB\-Xmaxjitcodesize\fR\&.
2371 .RE
2372 .PP
2373 \-XX:RTMAbortRatio=\fIabort_ratio\fR
2374 .RS 4
2375 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
2376 \fB\-XX:+UseRTMDeopt\fR
2377 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\&.
2378 .RE
2379 .PP
2380 \-XX:RTMRetryCount=\fInumber_of_retries\fR
2381 .RS 4
2382 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
2383 \fB\-XX:UseRTMLocking\fR
2384 option must be enabled\&.
2385 .RE
2386 .PP
2387 \-XX:\-TieredCompilation
2388 .RS 4
2389 Disables the use of tiered compilation\&. By default, this option is enabled\&. Only the Java HotSpot Server VM supports this option\&.
2390 .RE
2391 .PP
2392 \-XX:+UseAES
2393 .RS 4
2394 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\&.
2395 .RE
2396 .PP
2397 \-XX:+UseAESIntrinsics
2398 .RS 4
2399 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
2400 \fB\-XX:\-UseAES \-XX:\-UseAESIntrinsics\fR\&. For example, to enable hardware AES, use the following flags:
2401 .sp
2402 .if n \{\
2403 .RS 4
2404 .\}
2405 .nf
2406 \fB\-XX:+UseAES \-XX:+UseAESIntrinsics\fR
2407
2408 .fi
2409 .if n \{\
2410 .RE
2411 .\}
2412 To support UseAES and UseAESIntrinsics flags for 32\-bit and 64\-bit use
2413 \fB\-server\fR
2414 option to choose Java HotSpot Server VM\&. These flags are not supported on Client VM\&.
2415 .RE
2416 .PP
2417 \-XX:+UseCodeCacheFlushing
2418 .RS 4
2419 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
2420 \fB\-XX:\-UseCodeCacheFlushing\fR\&.
2421 .RE
2422 .PP
2423 \-XX:+UseCondCardMark
2424 .RS 4
2425 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\&.
2426 .RE
2427 .PP
2428 \-XX:+UseRTMDeopt
2429 .RS 4
2430 Auto\-tunes RTM locking depending on the abort ratio\&. This ratio is specified by
2431 \fB\-XX:RTMAbortRatio\fR
2432 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
2433 \fB\-XX:+UseRTMLocking\fR
2434 option must be enabled\&.
2435 .RE
2436 .PP
2437 \-XX:+UseRTMLocking
2438 .RS 4
2439 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)\&.
2440 .sp
2441 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
2442 \fBXBEGIN\fR,
2443 \fBXABORT\fR,
2444 \fBXEND\fR, and
2445 \fBXTEST\fR\&. The
2446 \fBXBEGIN\fR
2447 and
2448 \fBXEND\fR
2449 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
2450 \fBXEND\fR
2451 instruction\&. The
2452 \fBXABORT\fR
2453 instruction can be used to explicitly abort a transaction and the
2454 \fBXEND\fR
2455 instruction to check if a set of instructions are being run in a transaction\&.
2456 .sp
2457 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\&.
2458 .sp
2459 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\&.
2460 .RE
2461 .PP
2462 \-XX:+UseSHA
2463 .RS 4
2464 Enables hardware\-based intrinsics for SHA crypto hash functions for SPARC hardware\&.
2465 \fBUseSHA\fR
2466 is used in conjunction with the
2467 \fBUseSHA1Intrinsics\fR,
2468 \fBUseSHA256Intrinsics\fR, and
2469 \fBUseSHA512Intrinsics\fR
2470 options\&.
2471 .sp
2472 The
2473 \fBUseSHA\fR
2474 and
2475 \fBUseSHA*Intrinsics\fR
2476 flags are enabled by default, and are supported only for Java HotSpot Server VM 64\-bit on SPARC T4 and newer\&.
2477 .sp
2478 This feature is only applicable when using the
2479 \fBsun\&.security\&.provider\&.Sun\fR
2480 provider for SHA operations\&.
2481 .sp
2482 To disable all hardware\-based SHA intrinsics, specify
2483 \fB\-XX:\-UseSHA\fR\&. To disable only a particular SHA intrinsic, use the appropriate corresponding option\&. For example:
2484 \fB\-XX:\-UseSHA256Intrinsics\fR\&.
2485 .RE
2486 .PP
2487 \-XX:+UseSHA1Intrinsics
2488 .RS 4
2489 Enables intrinsics for SHA\-1 crypto hash function\&.
2490 .RE
2491 .PP
2492 \-XX:+UseSHA256Intrinsics
2493 .RS 4
2494 Enables intrinsics for SHA\-224 and SHA\-256 crypto hash functions\&.
2495 .RE
2496 .PP
2497 \-XX:+UseSHA512Intrinsics
2498 .RS 4
2499 Enables intrinsics for SHA\-384 and SHA\-512 crypto hash functions\&.
2500 .RE
2501 .PP
2502 \-XX:+UseSuperWord
2503 .RS 4
2504 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
2505 \fB\-XX:\-UseSuperWord\fR\&. Only the Java HotSpot Server VM supports this option\&.
2506 .RE
2507 .SS "Advanced Serviceability Options"
2508 .PP
2509 These options provide the ability to gather system information and perform extensive debugging\&.
2510 .PP
2511 \-XX:+ExtendedDTraceProbes
2512 .RS 4
2513 Enables additional
2514 \fBdtrace\fR
2515 tool probes that impact the performance\&. By default, this option is disabled and
2516 \fBdtrace\fR
2517 performs only standard probes\&.
2518 .RE
2519 .PP
2520 \-XX:+HeapDumpOnOutOfMemory
2521 .RS 4
2522 Enables the dumping of the Java heap to a file in the current directory by using the heap profiler (HPROF) when a
2523 \fBjava\&.lang\&.OutOfMemoryError\fR
2524 exception is thrown\&. You can explicitly set the heap dump file path and name using the
2525 \fB\-XX:HeapDumpPath\fR
2526 option\&. By default, this option is disabled and the heap is not dumped when an
2527 \fBOutOfMemoryError\fR
2528 exception is thrown\&.
2529 .RE
2530 .PP
2531 \-XX:HeapDumpPath=\fIpath\fR
2532 .RS 4
2533 Sets the path and file name for writing the heap dump provided by the heap profiler (HPROF) when the
2534 \fB\-XX:+HeapDumpOnOutOfMemoryError\fR
2535 option is set\&. By default, the file is created in the current working directory, and it is named
2536 \fBjava_pid\fR\fIpid\fR\fB\&.hprof\fR
2537 where
2538 \fIpid\fR
2539 is the identifier of the process that caused the error\&. The following example shows how to set the default file explicitly (\fB%p\fR
2540 represents the current process identificator):
2541 .sp
2542 .if n \{\
2543 .RS 4
2544 .\}
2545 .nf
2546 \fB\-XX:HeapDumpPath=\&./java_pid%p\&.hprof\fR
2547
2548 .fi
2549 .if n \{\
2550 .RE
2551 .\}
2552 The following example shows how to set the heap dump file to
2553 \fB/var/log/java/java_heapdump\&.hprof\fR:
2554 .sp
2555 .if n \{\
2556 .RS 4
2557 .\}
2558 .nf
2559 \fB\-XX:HeapDumpPath=/var/log/java/java_heapdump\&.hprof\fR
2560
2561 .fi
2562 .if n \{\
2563 .RE
2564 .\}
2565 .RE
2566 .PP
2567 \-XX:LogFile=\fIpath\fR
2568 .RS 4
2569 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
2570 \fBhotspot\&.log\fR\&.
2571 .sp
2572 The following example shows how to set the log file to
2573 \fB/var/log/java/hotspot\&.log\fR:
2574 .sp
2575 .if n \{\
2576 .RS 4
2577 .\}
2578 .nf
2579 \fB\-XX:LogFile=/var/log/java/hotspot\&.log\fR
2580
2581 .fi
2582 .if n \{\
2583 .RE
2584 .\}
2585 .RE
2586 .PP
2587 \-XX:+PrintClassHistogram
2588 .RS 4
2589 Enables printing of a class instance histogram after a
2590 \fBControl+C\fR
2591 event (\fBSIGTERM\fR)\&. By default, this option is disabled\&.
2592 .sp
2593 Setting this option is equivalent to running the
2594 \fBjmap \-histo\fR
2595 command, or the
2596 \fBjcmd \fR\fIpid\fR\fB GC\&.class_histogram\fR
2597 command, where
2598 \fIpid\fR
2599 is the current Java process identifier\&.
2600 .RE
2601 .PP
2602 \-XX:+PrintConcurrentLocks
2603 .RS 4
2604 Enables printing of locks after a event\&. By default, this option is disabled\&.
2605 .sp
2606 Enables printing of
2607 \fBjava\&.util\&.concurrent\fR
2608 locks after a
2609 \fBControl+C\fR
2610 event (\fBSIGTERM\fR)\&. By default, this option is disabled\&.
2611 .sp
2612 Setting this option is equivalent to running the
2613 \fBjstack \-l\fR
2614 command or the
2615 \fBjcmd \fR\fIpid\fR\fB Thread\&.print \-l\fR
2616 command, where
2617 \fIpid\fR
2618 is the current Java process identifier\&.
2619 .RE
2620 .PP
2621 \-XX:+UnlockDiagnosticVMOptions
2622 .RS 4
2623 Unlocks the options intended for diagnosing the JVM\&. By default, this option is disabled and diagnostic options are not available\&.
2624 .RE
2625 .SS "Advanced Garbage Collection Options"
2626 .PP
2627 These options control how garbage collection (GC) is performed by the Java HotSpot VM\&.
2628 .PP
2629 \-XX:+AggressiveHeap
2630 .RS 4
2631 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\&.
2632 .RE
2633 .PP
2634 \-XX:+AlwaysPreTouch
2635 .RS 4
2636 Enables touching of every page on the Java heap during JVM initialization\&. This gets all pages into the memory before entering the
2637 \fBmain()\fR
2638 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\&.
2639 .RE
2640 .PP
2641 \-XX:+CMSClassUnloadingEnabled
2642 .RS 4
2643 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
2644 \fB\-XX:\-CMSClassUnloadingEnabled\fR\&.
2645 .RE
2646 .PP
2647 \-XX:CMSExpAvgFactor=\fIpercent\fR
2648 .RS 4
2649 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%:
2650 .sp
2651 .if n \{\
2652 .RS 4
2653 .\}
2654 .nf
2655 \fB\-XX:CMSExpAvgFactor=15\fR
2656
2657 .fi
2658 .if n \{\
2659 .RE
2660 .\}
2661 .RE
2662 .PP
2663 \-XX:CMSInitiatingOccupancyFraction=\fIpercent\fR
2664 .RS 4
2665 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
2666 \fB\-XX:CMSTriggerRatio\fR
2667 is used to define the value of the initiating occupancy fraction\&.
2668 .sp
2669 The following example shows how to set the occupancy fraction to 20%:
2670 .sp
2671 .if n \{\
2672 .RS 4
2673 .\}
2674 .nf
2675 \fB\-XX:CMSInitiatingOccupancyFraction=20\fR
2676
2677 .fi
2678 .if n \{\
2679 .RE
2680 .\}
2681 .RE
2682 .PP
2683 \-XX:+CMSScavengeBeforeRemark
2684 .RS 4
2685 Enables scavenging attempts before the CMS remark step\&. By default, this option is disabled\&.
2686 .RE
2687 .PP
2688 \-XX:CMSTriggerRatio=\fIpercent\fR
2689 .RS 4
2690 Sets the percentage (0 to 100) of the value specified by
2691 \fB\-XX:MinHeapFreeRatio\fR
2692 that is allocated before a CMS collection cycle commences\&. The default value is set to 80%\&.
2693 .sp
2694 The following example shows how to set the occupancy fraction to 75%:
2695 .sp
2696 .if n \{\
2697 .RS 4
2698 .\}
2699 .nf
2700 \fB\-XX:CMSTriggerRatio=75\fR
2701
2702 .fi
2703 .if n \{\
2704 .RE
2705 .\}
2706 .RE
2707 .PP
2708 \-XX:ConcGCThreads=\fIthreads\fR
2709 .RS 4
2710 Sets the number of threads used for concurrent GC\&. The default value depends on the number of CPUs available to the JVM\&.
2711 .sp
2712 For example, to set the number of threads for concurrent GC to 2, specify the following option:
2713 .sp
2714 .if n \{\
2715 .RS 4
2716 .\}
2717 .nf
2718 \fB\-XX:ConcGCThreads=2\fR
2719
2720 .fi
2721 .if n \{\
2722 .RE
2723 .\}
2724 .RE
2725 .PP
2726 \-XX:+DisableExplicitGC
2727 .RS 4
2728 Enables the option that disables processing of calls to
2729 \fBSystem\&.gc()\fR\&. This option is disabled by default, meaning that calls to
2730 \fBSystem\&.gc()\fR
2731 are processed\&. If processing of calls to
2732 \fBSystem\&.gc()\fR
2733 is disabled, the JVM still performs GC when necessary\&.
2734 .RE
2735 .PP
2736 \-XX:+ExplicitGCInvokesConcurrent
2737 .RS 4
2738 Enables invoking of concurrent GC by using the
2739 \fBSystem\&.gc()\fR
2740 request\&. This option is disabled by default and can be enabled only together with the
2741 \fB\-XX:+UseConcMarkSweepGC\fR
2742 option\&.
2743 .RE
2744 .PP
2745 \-XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses
2746 .RS 4
2747 Enables invoking of concurrent GC by using the
2748 \fBSystem\&.gc()\fR
2749 request and unloading of classes during the concurrent GC cycle\&. This option is disabled by default and can be enabled only together with the
2750 \fB\-XX:+UseConcMarkSweepGC\fR
2751 option\&.
2752 .RE
2753 .PP
2754 \-XX:G1HeapRegionSize=\fIsize\fR
2755 .RS 4
2756 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\&.
2757 .sp
2758 The following example shows how to set the size of the subdivisions to 16 MB:
2759 .sp
2760 .if n \{\
2761 .RS 4
2762 .\}
2763 .nf
2764 \fB\-XX:G1HeapRegionSize=16m\fR
2765
2766 .fi
2767 .if n \{\
2768 .RE
2769 .\}
2770 .RE
2771 .PP
2772 \-XX:+G1PrintHeapRegions
2773 .RS 4
2774 Enables the printing of information about which regions are allocated and which are reclaimed by the G1 collector\&. By default, this option is disabled\&.
2775 .RE
2776 .PP
2777 \-XX:G1ReservePercent=\fIpercent\fR
2778 .RS 4
2779 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%\&.
2780 .sp
2781 The following example shows how to set the reserved heap to 20%:
2782 .sp
2783 .if n \{\
2784 .RS 4
2785 .\}
2786 .nf
2787 \fB\-XX:G1ReservePercent=20\fR
2788
2789 .fi
2790 .if n \{\
2791 .RE
2792 .\}
2793 .RE
2794 .PP
2795 \-XX:InitialHeapSize=\fIsize\fR
2796 .RS 4
2797 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
2798 \fBk\fR
2799 or
2800 \fBK\fR
2801 to indicate kilobytes,
2802 \fBm\fR
2803 or
2804 \fBM\fR
2805 to indicate megabytes,
2806 \fBg\fR
2807 or
2808 \fBG\fR
2809 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. See the section "Ergonomics" in
2810 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
2811 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
2812 .sp
2813 The following examples show how to set the size of allocated memory to 6 MB using various units:
2814 .sp
2815 .if n \{\
2816 .RS 4
2817 .\}
2818 .nf
2819 \fB\-XX:InitialHeapSize=6291456\fR
2820 \fB\-XX:InitialHeapSize=6144k\fR
2821 \fB\-XX:InitialHeapSize=6m\fR
2822
2823 .fi
2824 .if n \{\
2825 .RE
2826 .\}
2827 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
2828 \fB\-XX:NewSize\fR
2829 option\&.
2830 .RE
2831 .PP
2832 \-XX:InitialSurvivorRatio=\fIratio\fR
2833 .RS 4
2834 Sets the initial survivor space ratio used by the throughput garbage collector (which is enabled by the
2835 \fB\-XX:+UseParallelGC\fR
2836 and/or \-\fBXX:+UseParallelOldGC\fR
2837 options)\&. Adaptive sizing is enabled by default with the throughput garbage collector by using the
2838 \fB\-XX:+UseParallelGC\fR
2839 and
2840 \fB\-XX:+UseParallelOldGC\fR
2841 options, and survivor space is resized according to the application behavior, starting with the initial value\&. If adaptive sizing is disabled (using the
2842 \fB\-XX:\-UseAdaptiveSizePolicy\fR
2843 option), then the
2844 \fB\-XX:SurvivorRatio\fR
2845 option should be used to set the size of the survivor space for the entire execution of the application\&.
2846 .sp
2847 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):
2848 .sp
2849 .if n \{\
2850 .RS 4
2851 .\}
2852 .nf
2853 \fBS=Y/(R+2)\fR
2854
2855 .fi
2856 .if n \{\
2857 .RE
2858 .\}
2859 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\&.
2860 .sp
2861 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\&.
2862 .sp
2863 The following example shows how to set the initial survivor space ratio to 4:
2864 .sp
2865 .if n \{\
2866 .RS 4
2867 .\}
2868 .nf
2869 \fB\-XX:InitialSurvivorRatio=4\fR
2870
2871 .fi
2872 .if n \{\
2873 .RE
2874 .\}
2875 .RE
2876 .PP
2877 \-XX:InitiatingHeapOccupancyPercent=\fIpercent\fR
2878 .RS 4
2879 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)\&.
2880 .sp
2881 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%:
2882 .sp
2883 .if n \{\
2884 .RS 4
2885 .\}
2886 .nf
2887 \fB\-XX:InitiatingHeapOccupancyPercent=75\fR
2888
2889 .fi
2890 .if n \{\
2891 .RE
2892 .\}
2893 .RE
2894 .PP
2895 \-XX:MaxGCPauseMillis=\fItime\fR
2896 .RS 4
2897 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\&.
2898 .sp
2899 The following example shows how to set the maximum target pause time to 500 ms:
2900 .sp
2901 .if n \{\
2902 .RS 4
2903 .\}
2904 .nf
2905 \fB\-XX:MaxGCPauseMillis=500\fR
2906
2907 .fi
2908 .if n \{\
2909 .RE
2910 .\}
2911 .RE
2912 .PP
2913 \-XX:MaxHeapSize=\fIsize\fR
2914 .RS 4
2915 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
2916 \fBk\fR
2917 or
2918 \fBK\fR
2919 to indicate kilobytes,
2920 \fBm\fR
2921 or
2922 \fBM\fR
2923 to indicate megabytes,
2924 \fBg\fR
2925 or
2926 \fBG\fR
2927 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. For server deployments,
2928 \fB\-XX:InitialHeapSize\fR
2929 and
2930 \fB\-XX:MaxHeapSize\fR
2931 are often set to the same value\&. See the section "Ergonomics" in
2932 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
2933 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
2934 .sp
2935 The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:
2936 .sp
2937 .if n \{\
2938 .RS 4
2939 .\}
2940 .nf
2941 \fB\-XX:MaxHeapSize=83886080\fR
2942 \fB\-XX:MaxHeapSize=81920k\fR
2943 \fB\-XX:MaxHeapSize=80m\fR
2944
2945 .fi
2946 .if n \{\
2947 .RE
2948 .\}
2949 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\&.
2950 .sp
2951 The
2952 \fB\-XX:MaxHeapSize\fR
2953 option is equivalent to
2954 \fB\-Xmx\fR\&.
2955 .RE
2956 .PP
2957 \-XX:MaxHeapFreeRatio=\fIpercent\fR
2958 .RS 4
2959 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%\&.
2960 .sp
2961 The following example shows how to set the maximum free heap ratio to 75%:
2962 .sp
2963 .if n \{\
2964 .RS 4
2965 .\}
2966 .nf
2967 \fB\-XX:MaxHeapFreeRatio=75\fR
2968
2969 .fi
2970 .if n \{\
2971 .RE
2972 .\}
2973 .RE
2974 .PP
2975 \-XX:MaxMetaspaceSize=\fIsize\fR
2976 .RS 4
2977 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\&.
2978 .sp
2979 The following example shows how to set the maximum class metadata size to 256 MB:
2980 .sp
2981 .if n \{\
2982 .RS 4
2983 .\}
2984 .nf
2985 \fB\-XX:MaxMetaspaceSize=256m\fR
2986
2987 .fi
2988 .if n \{\
2989 .RE
2990 .\}
2991 .RE
2992 .PP
2993 \-XX:MaxNewSize=\fIsize\fR
2994 .RS 4
2995 Sets the maximum size (in bytes) of the heap for the young generation (nursery)\&. The default value is set ergonomically\&.
2996 .RE
2997 .PP
2998 \-XX:MaxTenuringThreshold=\fIthreshold\fR
2999 .RS 4
3000 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\&.
3001 .sp
3002 The following example shows how to set the maximum tenuring threshold to 10:
3003 .sp
3004 .if n \{\
3005 .RS 4
3006 .\}
3007 .nf
3008 \fB\-XX:MaxTenuringThreshold=10\fR
3009
3010 .fi
3011 .if n \{\
3012 .RE
3013 .\}
3014 .RE
3015 .PP
3016 \-XX:MetaspaceSize=\fIsize\fR
3017 .RS 4
3018 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\&.
3019 .RE
3020 .PP
3021 \-XX:MinHeapFreeRatio=\fIpercent\fR
3022 .RS 4
3023 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%\&.
3024 .sp
3025 The following example shows how to set the minimum free heap ratio to 25%:
3026 .sp
3027 .if n \{\
3028 .RS 4
3029 .\}
3030 .nf
3031 \fB\-XX:MinHeapFreeRatio=25\fR
3032
3033 .fi
3034 .if n \{\
3035 .RE
3036 .\}
3037 .RE
3038 .PP
3039 \-XX:NewRatio=\fIratio\fR
3040 .RS 4
3041 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:
3042 .sp
3043 .if n \{\
3044 .RS 4
3045 .\}
3046 .nf
3047 \fB\-XX:NewRatio=1\fR
3048
3049 .fi
3050 .if n \{\
3051 .RE
3052 .\}
3053 .RE
3054 .PP
3055 \-XX:NewSize=\fIsize\fR
3056 .RS 4
3057 Sets the initial size (in bytes) of the heap for the young generation (nursery)\&. Append the letter
3058 \fBk\fR
3059 or
3060 \fBK\fR
3061 to indicate kilobytes,
3062 \fBm\fR
3063 or
3064 \fBM\fR
3065 to indicate megabytes,
3066 \fBg\fR
3067 or
3068 \fBG\fR
3069 to indicate gigabytes\&.
3070 .sp
3071 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\&.
3072 .sp
3073 The following examples show how to set the initial size of young generation to 256 MB using various units:
3074 .sp
3075 .if n \{\
3076 .RS 4
3077 .\}
3078 .nf
3079 \fB\-XX:NewSize=256m\fR
3080 \fB\-XX:NewSize=262144k\fR
3081 \fB\-XX:NewSize=268435456\fR
3082
3083 .fi
3084 .if n \{\
3085 .RE
3086 .\}
3087 The
3088 \fB\-XX:NewSize\fR
3089 option is equivalent to
3090 \fB\-Xmn\fR\&.
3091 .RE
3092 .PP
3093 \-XX:ParallelGCThreads=\fIthreads\fR
3094 .RS 4
3095 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\&.
3096 .sp
3097 For example, to set the number of threads for parallel GC to 2, specify the following option:
3098 .sp
3099 .if n \{\
3100 .RS 4
3101 .\}
3102 .nf
3103 \fB\-XX:ParallelGCThreads=2\fR
3104
3105 .fi
3106 .if n \{\
3107 .RE
3108 .\}
3109 .RE
3110 .PP
3111 \-XX:+ParallelRefProcEnabled
3112 .RS 4
3113 Enables parallel reference processing\&. By default, this option is disabled\&.
3114 .RE
3115 .PP
3116 \-XX:+PrintAdaptiveSizePolicy
3117 .RS 4
3118 Enables printing of information about adaptive generation sizing\&. By default, this option is disabled\&.
3119 .RE
3120 .PP
3121 \-XX:+PrintGC
3122 .RS 4
3123 Enables printing of messages at every GC\&. By default, this option is disabled\&.
3124 .RE
3125 .PP
3126 \-XX:+PrintGCApplicationConcurrentTime
3127 .RS 4
3128 Enables printing of how much time elapsed since the last pause (for example, a GC pause)\&. By default, this option is disabled\&.
3129 .RE
3130 .PP
3131 \-XX:+PrintGCApplicationStoppedTime
3132 .RS 4
3133 Enables printing of how much time the pause (for example, a GC pause) lasted\&. By default, this option is disabled\&.
3134 .RE
3135 .PP
3136 \-XX:+PrintGCDateStamps
3137 .RS 4
3138 Enables printing of a date stamp at every GC\&. By default, this option is disabled\&.
3139 .RE
3140 .PP
3141 \-XX:+PrintGCDetails
3142 .RS 4
3143 Enables printing of detailed messages at every GC\&. By default, this option is disabled\&.
3144 .RE
3145 .PP
3146 \-XX:+PrintGCTaskTimeStamps
3147 .RS 4
3148 Enables printing of time stamps for every individual GC worker thread task\&. By default, this option is disabled\&.
3149 .RE
3150 .PP
3151 \-XX:+PrintGCTimeStamps
3152 .RS 4
3153 Enables printing of time stamps at every GC\&. By default, this option is disabled\&.
3154 .RE
3155 .PP
3156 \-XX:+PrintStringDeduplicationStatistics
3157 .RS 4
3158 Prints detailed deduplication statistics\&. By default, this option is disabled\&. See the
3159 \fB\-XX:+UseStringDeduplication\fR
3160 option\&.
3161 .RE
3162 .PP
3163 \-XX:+PrintTenuringDistribution
3164 .RS 4
3165 Enables printing of tenuring age information\&. The following is an example of the output:
3166 .sp
3167 .if n \{\
3168 .RS 4
3169 .\}
3170 .nf
3171 \fBDesired survivor size 48286924 bytes, new threshold 10 (max 10)\fR
3172 \fB\- age 1: 28992024 bytes, 28992024 total\fR
3173 \fB\- age 2: 1366864 bytes, 30358888 total\fR
3174 \fB\- age 3: 1425912 bytes, 31784800 total\fR
3175 \fB\&.\&.\&.\fR
3176
3177 .fi
3178 .if n \{\
3179 .RE
3180 .\}
3181 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\&.
3182 .sp
3183 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\&.
3184 .sp
3185 By default, this option is disabled\&.
3186 .RE
3187 .PP
3188 \-XX:+ScavengeBeforeFullGC
3189 .RS 4
3190 Enables GC of the young generation before each full GC\&. This option is enabled by default\&. Oracle recommends that you
3191 \fIdo not\fR
3192 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
3193 \fB\-XX:\-ScavengeBeforeFullGC\fR\&.
3194 .RE
3195 .PP
3196 \-XX:SoftRefLRUPolicyMSPerMB=\fItime\fR
3197 .RS 4
3198 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
3199 \fB\-XX:SoftRefLRUPolicyMSPerMB\fR
3200 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
3201 \fB\-Xmx\fR
3202 option has a significant effect on how quickly soft references are garbage collected\&.
3203 .sp
3204 The following example shows how to set the value to 2\&.5 seconds:
3205 .sp
3206 .if n \{\
3207 .RS 4
3208 .\}
3209 .nf
3210 \fB\-XX:SoftRefLRUPolicyMSPerMB=2500\fR
3211
3212 .fi
3213 .if n \{\
3214 .RE
3215 .\}
3216 .RE
3217 .PP
3218 \-XX:StringDeduplicationAgeThreshold=\fIthreshold\fR
3219 .RS 4
3220 \fBString\fR
3221 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
3222 \fB\-XX:+PrintTenuringDistribution\fR
3223 option\&. Note that
3224 \fBString\fR
3225 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
3226 \fB3\fR\&. See the
3227 \fB\-XX:+UseStringDeduplication\fR
3228 option\&.
3229 .RE
3230 .PP
3231 \-XX:SurvivorRatio=\fIratio\fR
3232 .RS 4
3233 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:
3234 .sp
3235 .if n \{\
3236 .RS 4
3237 .\}
3238 .nf
3239 \fB\-XX:SurvivorRatio=4\fR
3240
3241 .fi
3242 .if n \{\
3243 .RE
3244 .\}
3245 .RE
3246 .PP
3247 \-XX:TargetSurvivorRatio=\fIpercent\fR
3248 .RS 4
3249 Sets the desired percentage of survivor space (0 to 100) used after young garbage collection\&. By default, this option is set to 50%\&.
3250 .sp
3251 The following example shows how to set the target survivor space ratio to 30%:
3252 .sp
3253 .if n \{\
3254 .RS 4
3255 .\}
3256 .nf
3257 \fB\-XX:TargetSurvivorRatio=30\fR
3258
3259 .fi
3260 .if n \{\
3261 .RE
3262 .\}
3263 .RE
3264 .PP
3265 \-XX:TLABSize=\fIsize\fR
3266 .RS 4
3267 Sets the initial size (in bytes) of a thread\-local allocation buffer (TLAB)\&. Append the letter
3268 \fBk\fR
3269 or
3270 \fBK\fR
3271 to indicate kilobytes,
3272 \fBm\fR
3273 or
3274 \fBM\fR
3275 to indicate megabytes,
3276 \fBg\fR
3277 or
3278 \fBG\fR
3279 to indicate gigabytes\&. If this option is set to 0, then the JVM chooses the initial size automatically\&.
3280 .sp
3281 The following example shows how to set the initial TLAB size to 512 KB:
3282 .sp
3283 .if n \{\
3284 .RS 4
3285 .\}
3286 .nf
3287 \fB\-XX:TLABSize=512k\fR
3288
3289 .fi
3290 .if n \{\
3291 .RE
3292 .\}
3293 .RE
3294 .PP
3295 \-XX:+UseAdaptiveSizePolicy
3296 .RS 4
3297 Enables the use of adaptive generation sizing\&. This option is enabled by default\&. To disable adaptive generation sizing, specify
3298 \fB\-XX:\-UseAdaptiveSizePolicy\fR
3299 and set the size of the memory allocation pool explicitly (see the
3300 \fB\-XX:SurvivorRatio\fR
3301 option)\&.
3302 .RE
3303 .PP
3304 \-XX:+UseCMSInitiatingOccupancyOnly
3305 .RS 4
3306 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\&.
3307 .RE
3308 .PP
3309 \-XX:+UseConcMarkSweepGC
3310 .RS 4
3311 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\&.
3312 .sp
3313 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
3314 \fB\-XX:+UseParNewGC\fR
3315 option is automatically set and you should not disable it, because the following combination of options has been deprecated in JDK 8:
3316 \fB\-XX:+UseConcMarkSweepGC \-XX:\-UseParNewGC\fR\&.
3317 .RE
3318 .PP
3319 \-XX:+UseG1GC
3320 .RS 4
3321 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)\&.
3322 .sp
3323 By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM\&.
3324 .RE
3325 .PP
3326 \-XX:+UseGCOverheadLimit
3327 .RS 4
3328 Enables the use of a policy that limits the proportion of time spent by the JVM on GC before an
3329 \fBOutOfMemoryError\fR
3330 exception is thrown\&. This option is enabled, by default and the parallel GC will throw an
3331 \fBOutOfMemoryError\fR
3332 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
3333 \fB\-XX:\-UseGCOverheadLimit\fR\&.
3334 .RE
3335 .PP
3336 \-XX:+UseNUMA
3337 .RS 4
3338 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)\&.
3339 .RE
3340 .PP
3341 \-XX:+UseParallelGC
3342 .RS 4
3343 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\&.
3344 .sp
3345 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
3346 \fB\-XX:+UseParallelOldGC\fR
3347 option is automatically enabled, unless you explicitly disable it\&.
3348 .RE
3349 .PP
3350 \-XX:+UseParallelOldGC
3351 .RS 4
3352 Enables the use of the parallel garbage collector for full GCs\&. By default, this option is disabled\&. Enabling it automatically enables the
3353 \fB\-XX:+UseParallelGC\fR
3354 option\&.
3355 .RE
3356 .PP
3357 \-XX:+UseParNewGC
3358 .RS 4
3359 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
3360 \fB\-XX:+UseConcMarkSweepGC\fR
3361 option\&. Using the
3362 \fB\-XX:+UseParNewGC\fR
3363 option without the
3364 \fB\-XX:+UseConcMarkSweepGC\fR
3365 option was deprecated in JDK 8\&.
3366 .RE
3367 .PP
3368 \-XX:+UseSerialGC
3369 .RS 4
3370 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\&.
3371 .RE
3372 .PP
3373 \-XX:+UseSHM
3374 .RS 4
3375 On Linux, enables the JVM to use shared memory to setup large pages\&.
3376 .sp
3377 For more information, see "Large Pages"\&.
3378 .RE
3379 .PP
3380 \-XX:+UseStringDeduplication
3381 .RS 4
3382 Enables string deduplication\&. By default, this option is disabled\&. To use this option, you must enable the garbage\-first (G1) garbage collector\&. See the
3383 \fB\-XX:+UseG1GC\fR
3384 option\&.
3385 .sp
3386 \fIString deduplication\fR
3387 reduces the memory footprint of
3388 \fBString\fR
3389 objects on the Java heap by taking advantage of the fact that many
3390 \fBString\fR
3391 objects are identical\&. Instead of each
3392 \fBString\fR
3393 object pointing to its own character array, identical
3394 \fBString\fR
3395 objects can point to and share the same character array\&.
3396 .RE
3397 .PP
3398 \-XX:+UseTLAB
3399 .RS 4
3400 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
3401 \fB\-XX:\-UseTLAB\fR\&.
3402 .RE
3403 .SS "Deprecated and Removed Options"
3404 .PP
3405 These options were included in the previous release, but have since been considered unnecessary\&.
3406 .PP
3407 \-Xincgc
3408 .RS 4
3409 Enables incremental garbage collection\&. This option was deprecated in JDK 8 with no replacement\&.
3410 .RE
3411 .PP
3412 \-Xrun\fIlibname\fR
3413 .RS 4
3414 Loads the specified debugging/profiling library\&. This option was superseded by the
3415 \fB\-agentlib\fR
3416 option\&.
3417 .RE
3418 .PP
3419 \-XX:CMSIncrementalDutyCycle=\fIpercent\fR
3420 .RS 4
3421 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
3422 \fB\-XX:+CMSIncrementalMode\fR
3423 option\&.
3424 .RE
3425 .PP
3426 \-XX:CMSIncrementalDutyCycleMin=\fIpercent\fR
3427 .RS 4
3428 Sets the percentage of time (0 to 100) between minor collections that is the lower bound for the duty cycle when
3429 \fB\-XX:+CMSIncrementalPacing\fR
3430 is enabled\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3431 \fB\-XX:+CMSIncrementalMode\fR
3432 option\&.
3433 .RE
3434 .PP
3435 \-XX:+CMSIncrementalMode
3436 .RS 4
3437 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
3438 \fBCMSIncremental\fR\&.
3439 .RE
3440 .PP
3441 \-XX:CMSIncrementalOffset=\fIpercent\fR
3442 .RS 4
3443 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
3444 \fB\-XX:+CMSIncrementalMode\fR
3445 option\&.
3446 .RE
3447 .PP
3448 \-XX:+CMSIncrementalPacing
3449 .RS 4
3450 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
3451 \fB\-XX:+CMSIncrementalMode\fR
3452 option\&.
3453 .RE
3454 .PP
3455 \-XX:CMSIncrementalSafetyFactor=\fIpercent\fR
3456 .RS 4
3457 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
3458 \fB\-XX:+CMSIncrementalMode\fR
3459 option\&.
3460 .RE
3461 .PP
3462 \-XX:CMSInitiatingPermOccupancyFraction=\fIpercent\fR
3463 .RS 4
3464 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\&.
3465 .RE
3466 .PP
3467 \-XX:MaxPermSize=\fIsize\fR
3468 .RS 4
3469 Sets the maximum permanent generation space size (in bytes)\&. This option was deprecated in JDK 8, and superseded by the
3470 \fB\-XX:MaxMetaspaceSize\fR
3471 option\&.
3472 .RE
3473 .PP
3474 \-XX:PermSize=\fIsize\fR
3475 .RS 4
3476 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
3477 \fB\-XX:MetaspaceSize\fR
3478 option\&.
3479 .RE
3480 .PP
3481 \-XX:+UseSplitVerifier
3482 .RS 4
3483 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\&.
3484 .RE
3485 .PP
3486 \-XX:+UseStringCache
3487 .RS 4
3488 Enables caching of commonly allocated strings\&. This option was removed from JDK 8 with no replacement\&.
3489 .RE
3490 .SH "PERFORMANCE TUNING EXAMPLES"
3491 .PP
3492 The following examples show how to use experimental tuning flags to either optimize throughput or to provide lower response time\&.
3493 .PP
3494 \fBExample 1 \fRTuning for Higher Throughput
3495 .RS 4
3496 .sp
3497 .if n \{\
3498 .RS 4
3499 .\}
3500 .nf
3501 \fBjava \-d64 \-server \-XX:+AggressiveOpts \-XX:+UseLargePages \-Xmn10g \-Xms26g \-Xmx26g\fR
3502
3503 .fi
3504 .if n \{\
3505 .RE
3506 .\}
3507 .RE
3508 .PP
3509 \fBExample 2 \fRTuning for Lower Response Time
3510 .RS 4
3511 .sp
3512 .if n \{\
3513 .RS 4
3514 .\}
3515 .nf
3516 \fBjava \-d64 \-XX:+UseG1GC \-Xms26g Xmx26g \-XX:MaxGCPauseMillis=500 \-XX:+PrintGCTimeStamp\fR
3517
3518 .fi
3519 .if n \{\
3520 .RE
3521 .\}
3522 .RE
3523 .SH "LARGE PAGES"
3524 .PP
3525 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\&.
3526 .PP
3527 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\&.
3528 .PP
3529 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\&.
3530 .SS "Large Pages Support"
3531 .PP
3532 Solaris and Linux support large pages\&.
3533 .sp
3534 .it 1 an-trap
3535 .nr an-no-space-flag 1
3536 .nr an-break-flag 1
3537 .br
3538 .ps +1
3539 \fBSolaris\fR
3540 .RS 4
3541 .PP
3542 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\&.
3543 .RE
3544 .sp
3545 .it 1 an-trap
3546 .nr an-no-space-flag 1
3547 .nr an-break-flag 1
3548 .br
3549 .ps +1
3550 \fBLinux\fR
3551 .RS 4
3552 .PP
3553 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:
3554 .sp
3555 .if n \{\
3556 .RS 4
3557 .\}
3558 .nf
3559 \fB# cat /proc/meminfo | grep Huge\fR
3560 \fBHugePages_Total: 0\fR
3561 \fBHugePages_Free: 0\fR
3562 \fBHugepagesize: 2048 kB\fR
3563
3564 .fi
3565 .if n \{\
3566 .RE
3567 .\}
3568 .PP
3569 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
3570 \fBroot\fR, and then follow these steps:
3571 .sp
3572 .RS 4
3573 .ie n \{\
3574 \h'-04' 1.\h'+01'\c
3575 .\}
3576 .el \{\
3577 .sp -1
3578 .IP " 1." 4.2
3579 .\}
3580 If you are using the option
3581 \fB\-XX:+UseSHM\fR
3582 (instead of
3583 \fB\-XX:+UseHugeTLBFS\fR), then increase the
3584 \fBSHMMAX\fR
3585 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:
3586 .sp
3587 .if n \{\
3588 .RS 4
3589 .\}
3590 .nf
3591 \fB# echo 4294967295 > /proc/sys/kernel/shmmax\fR
3592
3593 .fi
3594 .if n \{\
3595 .RE
3596 .\}
3597 .RE
3598 .sp
3599 .RS 4
3600 .ie n \{\
3601 \h'-04' 2.\h'+01'\c
3602 .\}
3603 .el \{\
3604 .sp -1
3605 .IP " 2." 4.2
3606 .\}
3607 If you are using the option
3608 \fB\-XX:+UseSHM\fR
3609 or
3610 \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):
3611 .sp
3612 .if n \{\
3613 .RS 4
3614 .\}
3615 .nf
3616 \fB# echo 1536 > /proc/sys/vm/nr_hugepages\fR
3617
3618 .fi
3619 .if n \{\
3620 .RE
3621 .\}
3622 .RE
3623 .if n \{\
3624 .sp
3625 .\}
3626 .RS 4
3627 .it 1 an-trap
3628 .nr an-no-space-flag 1
3629 .nr an-break-flag 1
3630 .br
3631 .ps +1
3632 \fBNote\fR
3633 .ps -1
3634 .br
3635 .TS
3636 allbox tab(:);
3637 l.
3638 T{
3639 .sp
3640 .RS 4
3641 .ie n \{\
3642 \h'-04'\(bu\h'+03'\c
3643 .\}
3644 .el \{\
3645 .sp -1
3646 .IP \(bu 2.3
3647 .\}
3648 Note that the values contained in
3649 \fB/proc\fR
3650 will reset after you reboot your system, so may want to set them in an initialization script (for example,
3651 \fBrc\&.local\fR
3652 or
3653 \fBsysctl\&.conf\fR)\&.
3654 .RE
3655 .sp
3656 .RS 4
3657 .ie n \{\
3658 \h'-04'\(bu\h'+03'\c
3659 .\}
3660 .el \{\
3661 .sp -1
3662 .IP \(bu 2.3
3663 .\}
3664 If you configure (or resize) the OS kernel parameters
3665 \fB/proc/sys/kernel/shmmax\fR
3666 or
3667 \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:
3668 .sp
3669 .RS 4
3670 .ie n \{\
3671 \h'-04'\(bu\h'+03'\c
3672 .\}
3673 .el \{\
3674 .sp -1
3675 .IP \(bu 2.3
3676 .\}
3677 Java heap
3678 .RE
3679 .sp
3680 .RS 4
3681 .ie n \{\
3682 \h'-04'\(bu\h'+03'\c
3683 .\}
3684 .el \{\
3685 .sp -1
3686 .IP \(bu 2.3
3687 .\}
3688 Code cache
3689 .RE
3690 .sp
3691 .RS 4
3692 .ie n \{\
3693 \h'-04'\(bu\h'+03'\c
3694 .\}
3695 .el \{\
3696 .sp -1
3697 .IP \(bu 2.3
3698 .\}
3699 The marking bitmap data structure for the parallel GC
3700 .RE
3701 .sp
3702 Consequently, if you configure the
3703 \fBnr_hugepages\fR
3704 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\&.
3705 .RE
3706 T}
3707 .TE
3708 .sp 1
3709 .sp .5v
3710 .RE
3711 .RE
3712 .SH "EXIT STATUS"
3713 .PP
3714 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
3715 \fBSystem\&.exit(exitValue)\fR\&. The values are:
3716 .sp
3717 .RS 4
3718 .ie n \{\
3719 \h'-04'\(bu\h'+03'\c
3720 .\}
3721 .el \{\
3722 .sp -1
3723 .IP \(bu 2.3
3724 .\}
3725 \fB0\fR: Successful completion
3726 .RE
3727 .sp
3728 .RS 4
3729 .ie n \{\
3730 \h'-04'\(bu\h'+03'\c
3731 .\}
3732 .el \{\
3733 .sp -1
3734 .IP \(bu 2.3
3735 .\}
3736 \fB>0\fR: An error occurred
3737 .RE
3738 .SH "SEE ALSO"
3739 .sp
3740 .RS 4
3741 .ie n \{\
3742 \h'-04'\(bu\h'+03'\c
3743 .\}
3744 .el \{\
3745 .sp -1
3746 .IP \(bu 2.3
3747 .\}
3748 javac(1)
3749 .RE
3750 .sp
3751 .RS 4
3752 .ie n \{\
3753 \h'-04'\(bu\h'+03'\c
3754 .\}
3755 .el \{\
3756 .sp -1
3757 .IP \(bu 2.3
3758 .\}
3759 jdb(1)
3760 .RE
3761 .sp
3762 .RS 4
3763 .ie n \{\
3764 \h'-04'\(bu\h'+03'\c
3765 .\}
3766 .el \{\
3767 .sp -1
3768 .IP \(bu 2.3
3769 .\}
3770 javah(1)
3771 .RE
3772 .sp
3773 .RS 4
3774 .ie n \{\
3775 \h'-04'\(bu\h'+03'\c
3776 .\}
3777 .el \{\
3778 .sp -1
3779 .IP \(bu 2.3
3780 .\}
3781 jar(1)
3782 .RE
3783 .sp
3784 .RS 4
3785 .ie n \{\
3786 \h'-04'\(bu\h'+03'\c
3787 .\}
3788 .el \{\
3789 .sp -1
3790 .IP \(bu 2.3
3791 .\}
3792 jstat(1)
3793 .RE
3794 .br
3795 'pl 8.5i
3796 'bp