1 '\" t
2 .\" Copyright (c) 1994, 2018, Oracle and/or its affiliates. All rights reserved.
3 .\" DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 .\"
5 .\" This code is free software; you can redistribute it and/or modify it
6 .\" under the terms of the GNU General Public License version 2 only, as
7 .\" published by the Free Software Foundation.
8 .\"
9 .\" This code is distributed in the hope that it will be useful, but WITHOUT
10 .\" ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 .\" FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 .\" version 2 for more details (a copy is included in the LICENSE file that
13 .\" accompanied this code).
14 .\"
15 .\" You should have received a copy of the GNU General Public License version
16 .\" 2 along with this work; if not, write to the Free Software Foundation,
17 .\" Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 .\"
19 .\" Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 .\" or visit www.oracle.com if you need additional information or have any
21 .\" questions.
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:+DisableAttachMechanism
1177 .RS 4
1178 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
1179 \fBjcmd\fR,
1180 \fBjstack\fR,
1181 \fBjmap\fR, and
1182 \fBjinfo\fR\&.
1183 .RE
1184 .PP
1185 \-XX:ErrorFile=\fIfilename\fR
1186 .RS 4
1187 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
1188 \fBhs_err_pid\fR\fIpid\fR\fB\&.log\fR
1189 where
1190 \fIpid\fR
1191 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
1192 \fB%p\fR):
1193 .sp
1194 .if n \{\
1195 .RS 4
1196 .\}
1197 .nf
1198 \fB\-XX:ErrorFile=\&./hs_err_pid%p\&.log\fR
1199
1200 .fi
1201 .if n \{\
1202 .RE
1203 .\}
1204 The following example shows how to set the error log to
1205 \fB/var/log/java/java_error\&.log\fR:
1206 .sp
1207 .if n \{\
1208 .RS 4
1209 .\}
1210 .nf
1211 \fB\-XX:ErrorFile=/var/log/java/java_error\&.log\fR
1212
1213 .fi
1214 .if n \{\
1215 .RE
1216 .\}
1217 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
1218 \fB/tmp\fR\&.
1219 .RE
1220 .PP
1221 \-XX:+FailOverToOldVerifier
1222 .RS 4
1223 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\&.
1224 .RE
1225 .PP
1226 \-XX:LargePageSizeInBytes=\fIsize\fR
1227 .RS 4
1228 On Solaris, sets the maximum size (in bytes) for large pages used for Java heap\&. The
1229 \fIsize\fR
1230 argument must be a power of 2 (2, 4, 8, 16, \&.\&.\&.)\&. Append the letter
1231 \fBk\fR
1232 or
1233 \fBK\fR
1234 to indicate kilobytes,
1235 \fBm\fR
1236 or
1237 \fBM\fR
1238 to indicate megabytes,
1239 \fBg\fR
1240 or
1241 \fBG\fR
1242 to indicate gigabytes\&. By default, the size is set to 0, meaning that the JVM chooses the size for large pages automatically\&.
1243 .sp
1244 The following example illustrates how to set the large page size to 4 megabytes (MB):
1245 .sp
1246 .if n \{\
1247 .RS 4
1248 .\}
1249 .nf
1250 \fB\-XX:LargePageSizeInBytes=4m\fR
1251
1252 .fi
1253 .if n \{\
1254 .RE
1255 .\}
1256 .RE
1257 .PP
1258 \-XX:MaxDirectMemorySize=\fIsize\fR
1259 .RS 4
1260 Sets the maximum total size (in bytes) of the New I/O (the
1261 \fBjava\&.nio\fR
1262 package) direct\-buffer allocations\&. Append the letter
1263 \fBk\fR
1264 or
1265 \fBK\fR
1266 to indicate kilobytes,
1267 \fBm\fR
1268 or
1269 \fBM\fR
1270 to indicate megabytes,
1271 \fBg\fR
1272 or
1273 \fBG\fR
1274 to indicate gigabytes\&. By default, the size is set to 0, meaning that the JVM chooses the size for NIO direct\-buffer allocations automatically\&.
1275 .sp
1276 The following examples illustrate how to set the NIO size to 1024 KB in different units:
1277 .sp
1278 .if n \{\
1279 .RS 4
1280 .\}
1281 .nf
1282 \fB\-XX:MaxDirectMemorySize=1m\fR
1283 \fB\-XX:MaxDirectMemorySize=1024k\fR
1284 \fB\-XX:MaxDirectMemorySize=1048576\fR
1285
1286 .fi
1287 .if n \{\
1288 .RE
1289 .\}
1290 .RE
1291 .PP
1292 \-XX:NativeMemoryTracking=\fImode\fR
1293 .RS 4
1294 Specifies the mode for tracking JVM native memory usage\&. Possible
1295 \fImode\fR
1296 arguments for this option include the following:
1297 .PP
1298 off
1299 .RS 4
1300 Do not track JVM native memory usage\&. This is the default behavior if you do not specify the
1301 \fB\-XX:NativeMemoryTracking\fR
1302 option\&.
1303 .RE
1304 .PP
1305 summary
1306 .RS 4
1307 Only track memory usage by JVM subsystems, such as Java heap, class, code, and thread\&.
1308 .RE
1309 .PP
1310 detail
1311 .RS 4
1312 In addition to tracking memory usage by JVM subsystems, track memory usage by individual
1313 \fBCallSite\fR, individual virtual memory region and its committed regions\&.
1314 .RE
1315 .RE
1316 .PP
1317 \-XX:ObjectAlignmentInBytes=\fIalignment\fR
1318 .RS 4
1319 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\&.
1320 .sp
1321 The heap size limit in bytes is calculated as:
1322 .sp
1323 \fB4GB * ObjectAlignmentInBytes\fR
1324 .sp
1325 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\&.
1326 .RE
1327 .PP
1328 \-XX:OnError=\fIstring\fR
1329 .RS 4
1330 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\&.
1331 .sp
1332 The following example shows how the
1333 \fB\-XX:OnError\fR
1334 option can be used to run the
1335 \fBgcore\fR
1336 command to create the core image, and the debugger is started to attach to the process in case of an irrecoverable error (the
1337 \fB%p\fR
1338 designates the current process):
1339 .sp
1340 .if n \{\
1341 .RS 4
1342 .\}
1343 .nf
1344 \fB\-XX:OnError="gcore %p;dbx \- %p"\fR
1345
1346 .fi
1347 .if n \{\
1348 .RE
1349 .\}
1350 .RE
1351 .PP
1352 \-XX:OnOutOfMemoryError=\fIstring\fR
1353 .RS 4
1354 Sets a custom command or a series of semicolon\-separated commands to run when an
1355 \fBOutOfMemoryError\fR
1356 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
1357 \fB\-XX:OnError\fR
1358 option\&.
1359 .RE
1360 .PP
1361 \-XX:+PerfDataSaveToFile
1362 .RS 4
1363 If enabled, saves
1364 jstat(1) binary data when the Java application exits\&. This binary data is saved in a file named
1365 \fBhsperfdata_\fR\fI<pid>\fR, where
1366 \fI<pid>\fR
1367 is the process identifier of the Java application you ran\&. Use
1368 \fBjstat\fR
1369 to display the performance data contained in this file as follows:
1370 .sp
1371 .if n \{\
1372 .RS 4
1373 .\}
1374 .nf
1375 \fBjstat \-class file:///\fR\fB\fI<path>\fR\fR\fB/hsperfdata_\fR\fB\fI<pid>\fR\fR
1376 \fBjstat \-gc file:///\fR\fB\fI<path>\fR\fR\fB/hsperfdata_\fR\fB\fI<pid>\fR\fR
1377 .fi
1378 .if n \{\
1379 .RE
1380 .\}
1381 .RE
1382 .PP
1383 \-XX:+PrintCommandLineFlags
1384 .RS 4
1385 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\&.
1386 .RE
1387 .PP
1388 \-XX:+PrintNMTStatistics
1389 .RS 4
1390 Enables printing of collected native memory tracking data at JVM exit when native memory tracking is enabled (see
1391 \fB\-XX:NativeMemoryTracking\fR)\&. By default, this option is disabled and native memory tracking data is not printed\&.
1392 .RE
1393 .PP
1394 \-XX:+RelaxAccessControlCheck
1395 .RS 4
1396 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\&.
1397 .RE
1398 .PP
1399 \-XX:+ShowMessageBoxOnError
1400 .RS 4
1401 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\&.
1402 .RE
1403 .PP
1404 \-XX:ThreadStackSize=\fIsize\fR
1405 .RS 4
1406 Sets the thread stack size (in bytes)\&. Append the letter
1407 \fBk\fR
1408 or
1409 \fBK\fR
1410 to indicate kilobytes,
1411 \fBm\fR
1412 or
1413 \fBM\fR
1414 to indicate megabytes,
1415 \fBg\fR
1416 or
1417 \fBG\fR
1418 to indicate gigabytes\&. The default value depends on the platform:
1419 .sp
1420 .RS 4
1421 .ie n \{\
1422 \h'-04'\(bu\h'+03'\c
1423 .\}
1424 .el \{\
1425 .sp -1
1426 .IP \(bu 2.3
1427 .\}
1428 Linux/ARM (32\-bit): 320 KB
1429 .RE
1430 .sp
1431 .RS 4
1432 .ie n \{\
1433 \h'-04'\(bu\h'+03'\c
1434 .\}
1435 .el \{\
1436 .sp -1
1437 .IP \(bu 2.3
1438 .\}
1439 Linux/i386 (32\-bit): 320 KB
1440 .RE
1441 .sp
1442 .RS 4
1443 .ie n \{\
1444 \h'-04'\(bu\h'+03'\c
1445 .\}
1446 .el \{\
1447 .sp -1
1448 .IP \(bu 2.3
1449 .\}
1450 Linux/x64 (64\-bit): 1024 KB
1451 .RE
1452 .sp
1453 .RS 4
1454 .ie n \{\
1455 \h'-04'\(bu\h'+03'\c
1456 .\}
1457 .el \{\
1458 .sp -1
1459 .IP \(bu 2.3
1460 .\}
1461 OS X (64\-bit): 1024 KB
1462 .RE
1463 .sp
1464 .RS 4
1465 .ie n \{\
1466 \h'-04'\(bu\h'+03'\c
1467 .\}
1468 .el \{\
1469 .sp -1
1470 .IP \(bu 2.3
1471 .\}
1472 Oracle Solaris/i386 (32\-bit): 320 KB
1473 .RE
1474 .sp
1475 .RS 4
1476 .ie n \{\
1477 \h'-04'\(bu\h'+03'\c
1478 .\}
1479 .el \{\
1480 .sp -1
1481 .IP \(bu 2.3
1482 .\}
1483 Oracle Solaris/x64 (64\-bit): 1024 KB
1484 .RE
1485 .sp
1486 The following examples show how to set the thread stack size to 1024 KB in different units:
1487 .sp
1488 .if n \{\
1489 .RS 4
1490 .\}
1491 .nf
1492 \fB\-XX:ThreadStackSize=1m\fR
1493 \fB\-XX:ThreadStackSize=1024k\fR
1494 \fB\-XX:ThreadStackSize=1048576\fR
1495
1496 .fi
1497 .if n \{\
1498 .RE
1499 .\}
1500 This option is equivalent to
1501 \fB\-Xss\fR\&.
1502 .RE
1503 .PP
1504 \-XX:+TraceClassLoading
1505 .RS 4
1506 Enables tracing of classes as they are loaded\&. By default, this option is disabled and classes are not traced\&.
1507 .RE
1508 .PP
1509 \-XX:+TraceClassLoadingPreorder
1510 .RS 4
1511 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\&.
1512 .RE
1513 .PP
1514 \-XX:+TraceClassResolution
1515 .RS 4
1516 Enables tracing of constant pool resolutions\&. By default, this option is disabled and constant pool resolutions are not traced\&.
1517 .RE
1518 .PP
1519 \-XX:+TraceClassUnloading
1520 .RS 4
1521 Enables tracing of classes as they are unloaded\&. By default, this option is disabled and classes are not traced\&.
1522 .RE
1523 .PP
1524 \-XX:+TraceLoaderConstraints
1525 .RS 4
1526 Enables tracing of the loader constraints recording\&. By default, this option is disabled and loader constraints recording is not traced\&.
1527 .RE
1528 .PP
1529 \-XX:+UseAltSigs
1530 .RS 4
1531 Enables the use of alternative signals instead of
1532 \fBSIGUSR1\fR
1533 and
1534 \fBSIGUSR2\fR
1535 for JVM internal signals\&. By default, this option is disabled and alternative signals are not used\&. This option is equivalent to
1536 \fB\-Xusealtsigs\fR\&.
1537 .RE
1538 .PP
1539 \-XX:\-UseBiasedLocking
1540 .RS 4
1541 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
1542 .sp
1543 By default, this option is enabled\&.
1544 .RE
1545 .PP
1546 \-XX:\-UseCompressedOops
1547 .RS 4
1548 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\&.
1549 .sp
1550 It is also possible to use compressed pointers when Java heap sizes are greater than 32GB\&. See the
1551 \fB\-XX:ObjectAlignmentInBytes\fR
1552 option\&.
1553 .RE
1554 .PP
1555 \-XX:+UseHugeTLBFS
1556 .RS 4
1557 This option for Linux is the equivalent of specifying
1558 \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
1559 \fB\-XX:UseTransparentHugePages\fR
1560 if you want this behavior\&.
1561 .sp
1562 For more information, see "Large Pages"\&.
1563 .RE
1564 .PP
1565 \-XX:+UseLargePages
1566 .RS 4
1567 Enables the use of large page memory\&. By default, this option is disabled and large page memory is not used\&.
1568 .sp
1569 For more information, see "Large Pages"\&.
1570 .RE
1571 .PP
1572 \-XX:+UseMembar
1573 .RS 4
1574 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\&.)
1575 .RE
1576 .PP
1577 \-XX:+UsePerfData
1578 .RS 4
1579 Enables the
1580 \fBperfdata\fR
1581 feature\&. This option is enabled by default to allow JVM monitoring and performance testing\&. Disabling it suppresses the creation of the
1582 \fBhsperfdata_userid\fR
1583 directories\&. To disable the
1584 \fBperfdata\fR
1585 feature, specify
1586 \fB\-XX:\-UsePerfData\fR\&.
1587 .RE
1588 .PP
1589 \-XX:+UseTransparentHugePages
1590 .RS 4
1591 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\&.
1592 .sp
1593 For more information, see "Large Pages"\&.
1594 .RE
1595 .PP
1596 \-XX:+AllowUserSignalHandlers
1597 .RS 4
1598 Enables installation of signal handlers by the application\&. By default, this option is disabled and the application is not allowed to install signal handlers\&.
1599 .RE
1600 .SS "Advanced JIT Compiler Options"
1601 .PP
1602 These options control the dynamic just\-in\-time (JIT) compilation performed by the Java HotSpot VM\&.
1603 .PP
1604 \-XX:AllocateInstancePrefetchLines=\fIlines\fR
1605 .RS 4
1606 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:
1607 .sp
1608 .if n \{\
1609 .RS 4
1610 .\}
1611 .nf
1612 \fB\-XX:AllocateInstancePrefetchLines=1\fR
1613
1614 .fi
1615 .if n \{\
1616 .RE
1617 .\}
1618 Only the Java HotSpot Server VM supports this option\&.
1619 .RE
1620 .PP
1621 \-XX:AllocatePrefetchDistance=\fIsize\fR
1622 .RS 4
1623 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\&.
1624 .sp
1625 Negative values denote that prefetch distance is chosen based on the platform\&. Positive values are bytes to prefetch\&. Append the letter
1626 \fBk\fR
1627 or
1628 \fBK\fR
1629 to indicate kilobytes,
1630 \fBm\fR
1631 or
1632 \fBM\fR
1633 to indicate megabytes,
1634 \fBg\fR
1635 or
1636 \fBG\fR
1637 to indicate gigabytes\&. The default value is set to \-1\&.
1638 .sp
1639 The following example shows how to set the prefetch distance to 1024 bytes:
1640 .sp
1641 .if n \{\
1642 .RS 4
1643 .\}
1644 .nf
1645 \fB\-XX:AllocatePrefetchDistance=1024\fR
1646
1647 .fi
1648 .if n \{\
1649 .RE
1650 .\}
1651 Only the Java HotSpot Server VM supports this option\&.
1652 .RE
1653 .PP
1654 \-XX:AllocatePrefetchInstr=\fIinstruction\fR
1655 .RS 4
1656 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:
1657 .sp
1658 .if n \{\
1659 .RS 4
1660 .\}
1661 .nf
1662 \fB\-XX:AllocatePrefetchInstr=0\fR
1663
1664 .fi
1665 .if n \{\
1666 .RE
1667 .\}
1668 Only the Java HotSpot Server VM supports this option\&.
1669 .RE
1670 .PP
1671 \-XX:AllocatePrefetchLines=\fIlines\fR
1672 .RS 4
1673 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\&.
1674 .sp
1675 The following example shows how to set the number of loaded cache lines to 5:
1676 .sp
1677 .if n \{\
1678 .RS 4
1679 .\}
1680 .nf
1681 \fB\-XX:AllocatePrefetchLines=5\fR
1682
1683 .fi
1684 .if n \{\
1685 .RE
1686 .\}
1687 Only the Java HotSpot Server VM supports this option\&.
1688 .RE
1689 .PP
1690 \-XX:AllocatePrefetchStepSize=\fIsize\fR
1691 .RS 4
1692 Sets the step size (in bytes) for sequential prefetch instructions\&. Append the letter
1693 \fBk\fR
1694 or
1695 \fBK\fR
1696 to indicate kilobytes,
1697 \fBm\fR
1698 or
1699 \fBM\fR
1700 to indicate megabytes,
1701 \fBg\fR
1702 or
1703 \fBG\fR
1704 to indicate gigabytes\&. By default, the step size is set to 16 bytes:
1705 .sp
1706 .if n \{\
1707 .RS 4
1708 .\}
1709 .nf
1710 \fB\-XX:AllocatePrefetchStepSize=16\fR
1711
1712 .fi
1713 .if n \{\
1714 .RE
1715 .\}
1716 Only the Java HotSpot Server VM supports this option\&.
1717 .RE
1718 .PP
1719 \-XX:AllocatePrefetchStyle=\fIstyle\fR
1720 .RS 4
1721 Sets the generated code style for prefetch instructions\&. The
1722 \fIstyle\fR
1723 argument is an integer from 0 to 3:
1724 .PP
1725 0
1726 .RS 4
1727 Do not generate prefetch instructions\&.
1728 .RE
1729 .PP
1730 1
1731 .RS 4
1732 Execute prefetch instructions after each allocation\&. This is the default parameter\&.
1733 .RE
1734 .PP
1735 2
1736 .RS 4
1737 Use the thread\-local allocation block (TLAB) watermark pointer to determine when prefetch instructions are executed\&.
1738 .RE
1739 .PP
1740 3
1741 .RS 4
1742 Use BIS instruction on SPARC for allocation prefetch\&.
1743 .RE
1744 .sp
1745 Only the Java HotSpot Server VM supports this option\&.
1746 .RE
1747 .PP
1748 \-XX:+BackgroundCompilation
1749 .RS 4
1750 Enables background compilation\&. This option is enabled by default\&. To disable background compilation, specify
1751 \fB\-XX:\-BackgroundCompilation\fR
1752 (this is equivalent to specifying
1753 \fB\-Xbatch\fR)\&.
1754 .RE
1755 .PP
1756 \-XX:CICompilerCount=\fIthreads\fR
1757 .RS 4
1758 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:
1759 .sp
1760 .if n \{\
1761 .RS 4
1762 .\}
1763 .nf
1764 \fB\-XX:CICompilerCount=2\fR
1765
1766 .fi
1767 .if n \{\
1768 .RE
1769 .\}
1770 .RE
1771 .PP
1772 \-XX:CodeCacheMinimumFreeSpace=\fIsize\fR
1773 .RS 4
1774 Sets the minimum free space (in bytes) required for compilation\&. Append the letter
1775 \fBk\fR
1776 or
1777 \fBK\fR
1778 to indicate kilobytes,
1779 \fBm\fR
1780 or
1781 \fBM\fR
1782 to indicate megabytes,
1783 \fBg\fR
1784 or
1785 \fBG\fR
1786 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:
1787 .sp
1788 .if n \{\
1789 .RS 4
1790 .\}
1791 .nf
1792 \fB\-XX:CodeCacheMinimumFreeSpace=1024m\fR
1793
1794 .fi
1795 .if n \{\
1796 .RE
1797 .\}
1798 .RE
1799 .PP
1800 \-XX:CompileCommand=\fIcommand\fR,\fImethod\fR[,\fIoption\fR]
1801 .RS 4
1802 Specifies a command to perform on a method\&. For example, to exclude the
1803 \fBindexOf()\fR
1804 method of the
1805 \fBString\fR
1806 class from being compiled, use the following:
1807 .sp
1808 .if n \{\
1809 .RS 4
1810 .\}
1811 .nf
1812 \fB\-XX:CompileCommand=exclude,java/lang/String\&.indexOf\fR
1813
1814 .fi
1815 .if n \{\
1816 .RE
1817 .\}
1818 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
1819 \fB\-XX:+PrintCompilation\fR
1820 and
1821 \fB\-XX:+LogCompilation\fR
1822 options:
1823 .sp
1824 .if n \{\
1825 .RS 4
1826 .\}
1827 .nf
1828 \fB\-XX:CompileCommand=exclude,java\&.lang\&.String::indexOf\fR
1829
1830 .fi
1831 .if n \{\
1832 .RE
1833 .\}
1834 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
1835 \fBindexOf(String)\fR
1836 method of the
1837 \fBString\fR
1838 class from being compiled, use the following:
1839 .sp
1840 .if n \{\
1841 .RS 4
1842 .\}
1843 .nf
1844 \fB\-XX:CompileCommand="exclude,java/lang/String\&.indexOf,(Ljava/lang/String;)I"\fR
1845
1846 .fi
1847 .if n \{\
1848 .RE
1849 .\}
1850 You can also use the asterisk (*) as a wildcard for class and method names\&. For example, to exclude all
1851 \fBindexOf()\fR
1852 methods in all classes from being compiled, use the following:
1853 .sp
1854 .if n \{\
1855 .RS 4
1856 .\}
1857 .nf
1858 \fB\-XX:CompileCommand=exclude,*\&.indexOf\fR
1859
1860 .fi
1861 .if n \{\
1862 .RE
1863 .\}
1864 The commas and periods are aliases for spaces, making it easier to pass compiler commands through a shell\&. You can pass arguments to
1865 \fB\-XX:CompileCommand\fR
1866 using spaces as separators by enclosing the argument in quotation marks:
1867 .sp
1868 .if n \{\
1869 .RS 4
1870 .\}
1871 .nf
1872 \fB\-XX:CompileCommand="exclude java/lang/String indexOf"\fR
1873
1874 .fi
1875 .if n \{\
1876 .RE
1877 .\}
1878 Note that after parsing the commands passed on the command line using the
1879 \fB\-XX:CompileCommand\fR
1880 options, the JIT compiler then reads commands from the
1881 \fB\&.hotspot_compiler\fR
1882 file\&. You can add commands to this file or specify a different file using the
1883 \fB\-XX:CompileCommandFile\fR
1884 option\&.
1885 .sp
1886 To add several commands, either specify the
1887 \fB\-XX:CompileCommand\fR
1888 option multiple times, or separate each argument with the newline separator (\fB\en\fR)\&. The following commands are available:
1889 .PP
1890 break
1891 .RS 4
1892 Set a breakpoint when debugging the JVM to stop at the beginning of compilation of the specified method\&.
1893 .RE
1894 .PP
1895 compileonly
1896 .RS 4
1897 Exclude all methods from compilation except for the specified method\&. As an alternative, you can use the
1898 \fB\-XX:CompileOnly\fR
1899 option, which allows to specify several methods\&.
1900 .RE
1901 .PP
1902 dontinline
1903 .RS 4
1904 Prevent inlining of the specified method\&.
1905 .RE
1906 .PP
1907 exclude
1908 .RS 4
1909 Exclude the specified method from compilation\&.
1910 .RE
1911 .PP
1912 help
1913 .RS 4
1914 Print a help message for the
1915 \fB\-XX:CompileCommand\fR
1916 option\&.
1917 .RE
1918 .PP
1919 inline
1920 .RS 4
1921 Attempt to inline the specified method\&.
1922 .RE
1923 .PP
1924 log
1925 .RS 4
1926 Exclude compilation logging (with the
1927 \fB\-XX:+LogCompilation\fR
1928 option) for all methods except for the specified method\&. By default, logging is performed for all compiled methods\&.
1929 .RE
1930 .PP
1931 option
1932 .RS 4
1933 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
1934 \fBBlockLayoutByFrequency\fR
1935 option for the
1936 \fBappend()\fR
1937 method of the
1938 \fBStringBuffer\fR
1939 class, use the following:
1940 .sp
1941 .if n \{\
1942 .RS 4
1943 .\}
1944 .nf
1945 \fB\-XX:CompileCommand=option,java/lang/StringBuffer\&.append,BlockLayoutByFrequency\fR
1946
1947 .fi
1948 .if n \{\
1949 .RE
1950 .\}
1951 You can specify multiple compilation options, separated by commas or spaces\&.
1952 .RE
1953 .PP
1954 print
1955 .RS 4
1956 Print generated assembler code after compilation of the specified method\&.
1957 .RE
1958 .PP
1959 quiet
1960 .RS 4
1961 Do not print the compile commands\&. By default, the commands that you specify with the \-\fBXX:CompileCommand\fR
1962 option are printed; for example, if you exclude from compilation the
1963 \fBindexOf()\fR
1964 method of the
1965 \fBString\fR
1966 class, then the following will be printed to standard output:
1967 .sp
1968 .if n \{\
1969 .RS 4
1970 .\}
1971 .nf
1972 \fBCompilerOracle: exclude java/lang/String\&.indexOf\fR
1973
1974 .fi
1975 .if n \{\
1976 .RE
1977 .\}
1978 You can suppress this by specifying the
1979 \fB\-XX:CompileCommand=quiet\fR
1980 option before other
1981 \fB\-XX:CompileCommand\fR
1982 options\&.
1983 .RE
1984 .RE
1985 .PP
1986 \-XX:CompileCommandFile=\fIfilename\fR
1987 .RS 4
1988 Sets the file from which JIT compiler commands are read\&. By default, the
1989 \fB\&.hotspot_compiler\fR
1990 file is used to store commands performed by the JIT compiler\&.
1991 .sp
1992 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
1993 \fBtoString()\fR
1994 method of the
1995 \fBString\fR
1996 class:
1997 .sp
1998 .if n \{\
1999 .RS 4
2000 .\}
2001 .nf
2002 \fBprint java/lang/String toString\fR
2003
2004 .fi
2005 .if n \{\
2006 .RE
2007 .\}
2008 For more information about specifying the commands for the JIT compiler to perform on methods, see the
2009 \fB\-XX:CompileCommand\fR
2010 option\&.
2011 .RE
2012 .PP
2013 \-XX:CompileOnly=\fImethods\fR
2014 .RS 4
2015 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
2016 \fBlength()\fR
2017 method of the
2018 \fBString\fR
2019 class and the
2020 \fBsize()\fR
2021 method of the
2022 \fBList\fR
2023 class, use the following:
2024 .sp
2025 .if n \{\
2026 .RS 4
2027 .\}
2028 .nf
2029 \fB\-XX:CompileOnly=java/lang/String\&.length,java/util/List\&.size\fR
2030
2031 .fi
2032 .if n \{\
2033 .RE
2034 .\}
2035 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
2036 \fB\-XX:+PrintCompilation\fR
2037 and
2038 \fB\-XX:+LogCompilation\fR
2039 options:
2040 .sp
2041 .if n \{\
2042 .RS 4
2043 .\}
2044 .nf
2045 \fB\-XX:CompileOnly=java\&.lang\&.String::length,java\&.util\&.List::size\fR
2046
2047 .fi
2048 .if n \{\
2049 .RE
2050 .\}
2051 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:
2052 .sp
2053 .if n \{\
2054 .RS 4
2055 .\}
2056 .nf
2057 \fB\-XX:CompileOnly=java/lang/String\fR
2058 \fB\-XX:CompileOnly=java/lang\fR
2059 \fB\-XX:CompileOnly=\&.length\fR
2060
2061 .fi
2062 .if n \{\
2063 .RE
2064 .\}
2065 .RE
2066 .PP
2067 \-XX:CompileThreshold=\fIinvocations\fR
2068 .RS 4
2069 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
2070 \fB\-XX:+TieredCompilation\fR\&. The following example shows how to set the number of interpreted method invocations to 5,000:
2071 .sp
2072 .if n \{\
2073 .RS 4
2074 .\}
2075 .nf
2076 \fB\-XX:CompileThreshold=5000\fR
2077
2078 .fi
2079 .if n \{\
2080 .RE
2081 .\}
2082 You can completely disable interpretation of Java methods before compilation by specifying the
2083 \fB\-Xcomp\fR
2084 option\&.
2085 .RE
2086 .PP
2087 \-XX:+DoEscapeAnalysis
2088 .RS 4
2089 Enables the use of escape analysis\&. This option is enabled by default\&. To disable the use of escape analysis, specify
2090 \fB\-XX:\-DoEscapeAnalysis\fR\&. Only the Java HotSpot Server VM supports this option\&.
2091 .RE
2092 .PP
2093 \-XX:InitialCodeCacheSize=\fIsize\fR
2094 .RS 4
2095 Sets the initial code cache size (in bytes)\&. Append the letter
2096 \fBk\fR
2097 or
2098 \fBK\fR
2099 to indicate kilobytes,
2100 \fBm\fR
2101 or
2102 \fBM\fR
2103 to indicate megabytes,
2104 \fBg\fR
2105 or
2106 \fBG\fR
2107 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:
2108 .sp
2109 .if n \{\
2110 .RS 4
2111 .\}
2112 .nf
2113 \fB\-XX:InitialCodeCacheSize=32k\fR
2114
2115 .fi
2116 .if n \{\
2117 .RE
2118 .\}
2119 .RE
2120 .PP
2121 \-XX:+Inline
2122 .RS 4
2123 Enables method inlining\&. This option is enabled by default to increase performance\&. To disable method inlining, specify
2124 \fB\-XX:\-Inline\fR\&.
2125 .RE
2126 .PP
2127 \-XX:InlineSmallCode=\fIsize\fR
2128 .RS 4
2129 Sets the maximum code size (in bytes) for compiled methods that should be inlined\&. Append the letter
2130 \fBk\fR
2131 or
2132 \fBK\fR
2133 to indicate kilobytes,
2134 \fBm\fR
2135 or
2136 \fBM\fR
2137 to indicate megabytes,
2138 \fBg\fR
2139 or
2140 \fBG\fR
2141 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:
2142 .sp
2143 .if n \{\
2144 .RS 4
2145 .\}
2146 .nf
2147 \fB\-XX:InlineSmallCode=1000\fR
2148
2149 .fi
2150 .if n \{\
2151 .RE
2152 .\}
2153 .RE
2154 .PP
2155 \-XX:+LogCompilation
2156 .RS 4
2157 Enables logging of compilation activity to a file named
2158 \fBhotspot\&.log\fR
2159 in the current working directory\&. You can specify a different log file path and name using the
2160 \fB\-XX:LogFile\fR
2161 option\&.
2162 .sp
2163 By default, this option is disabled and compilation activity is not logged\&. The
2164 \fB\-XX:+LogCompilation\fR
2165 option has to be used together with the
2166 \fB\-XX:UnlockDiagnosticVMOptions\fR
2167 option that unlocks diagnostic JVM options\&.
2168 .sp
2169 You can enable verbose diagnostic output with a message printed to the console every time a method is compiled by using the
2170 \fB\-XX:+PrintCompilation\fR
2171 option\&.
2172 .RE
2173 .PP
2174 \-XX:MaxInlineSize=\fIsize\fR
2175 .RS 4
2176 Sets the maximum bytecode size (in bytes) of a method to be inlined\&. Append the letter
2177 \fBk\fR
2178 or
2179 \fBK\fR
2180 to indicate kilobytes,
2181 \fBm\fR
2182 or
2183 \fBM\fR
2184 to indicate megabytes,
2185 \fBg\fR
2186 or
2187 \fBG\fR
2188 to indicate gigabytes\&. By default, the maximum bytecode size is set to 35 bytes:
2189 .sp
2190 .if n \{\
2191 .RS 4
2192 .\}
2193 .nf
2194 \fB\-XX:MaxInlineSize=35\fR
2195
2196 .fi
2197 .if n \{\
2198 .RE
2199 .\}
2200 .RE
2201 .PP
2202 \-XX:MaxNodeLimit=\fInodes\fR
2203 .RS 4
2204 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:
2205 .sp
2206 .if n \{\
2207 .RS 4
2208 .\}
2209 .nf
2210 \fB\-XX:MaxNodeLimit=65000\fR
2211
2212 .fi
2213 .if n \{\
2214 .RE
2215 .\}
2216 .RE
2217 .PP
2218 \-XX:MaxTrivialSize=\fIsize\fR
2219 .RS 4
2220 Sets the maximum bytecode size (in bytes) of a trivial method to be inlined\&. Append the letter
2221 \fBk\fR
2222 or
2223 \fBK\fR
2224 to indicate kilobytes,
2225 \fBm\fR
2226 or
2227 \fBM\fR
2228 to indicate megabytes,
2229 \fBg\fR
2230 or
2231 \fBG\fR
2232 to indicate gigabytes\&. By default, the maximum bytecode size of a trivial method is set to 6 bytes:
2233 .sp
2234 .if n \{\
2235 .RS 4
2236 .\}
2237 .nf
2238 \fB\-XX:MaxTrivialSize=6\fR
2239
2240 .fi
2241 .if n \{\
2242 .RE
2243 .\}
2244 .RE
2245 .PP
2246 \-XX:+OptimizeStringConcat
2247 .RS 4
2248 Enables the optimization of
2249 \fBString\fR
2250 concatenation operations\&. This option is enabled by default\&. To disable the optimization of
2251 \fBString\fR
2252 concatenation operations, specify
2253 \fB\-XX:\-OptimizeStringConcat\fR\&. Only the Java HotSpot Server VM supports this option\&.
2254 .RE
2255 .PP
2256 \-XX:+PrintAssembly
2257 .RS 4
2258 Enables printing of assembly code for bytecoded and native methods by using the external
2259 \fBdisassembler\&.so\fR
2260 library\&. This enables you to see the generated code, which may help you to diagnose performance issues\&.
2261 .sp
2262 By default, this option is disabled and assembly code is not printed\&. The
2263 \fB\-XX:+PrintAssembly\fR
2264 option has to be used together with the
2265 \fB\-XX:UnlockDiagnosticVMOptions\fR
2266 option that unlocks diagnostic JVM options\&.
2267 .RE
2268 .PP
2269 \-XX:+PrintCompilation
2270 .RS 4
2271 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\&.
2272 .sp
2273 You can also log compilation activity to a file by using the
2274 \fB\-XX:+LogCompilation\fR
2275 option\&.
2276 .RE
2277 .PP
2278 \-XX:+PrintInlining
2279 .RS 4
2280 Enables printing of inlining decisions\&. This enables you to see which methods are getting inlined\&.
2281 .sp
2282 By default, this option is disabled and inlining information is not printed\&. The
2283 \fB\-XX:+PrintInlining\fR
2284 option has to be used together with the
2285 \fB\-XX:+UnlockDiagnosticVMOptions\fR
2286 option that unlocks diagnostic JVM options\&.
2287 .RE
2288 .PP
2289 \-XX:ReservedCodeCacheSize=\fIsize\fR
2290 .RS 4
2291 Sets the maximum code cache size (in bytes) for JIT\-compiled code\&. Append the letter
2292 \fBk\fR
2293 or
2294 \fBK\fR
2295 to indicate kilobytes,
2296 \fBm\fR
2297 or
2298 \fBM\fR
2299 to indicate megabytes,
2300 \fBg\fR
2301 or
2302 \fBG\fR
2303 to indicate gigabytes\&. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option
2304 \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
2305 \fB\-XX:InitialCodeCacheSize\fR\&. This option is equivalent to
2306 \fB\-Xmaxjitcodesize\fR\&.
2307 .RE
2308 .PP
2309 \-XX:RTMAbortRatio=\fIabort_ratio\fR
2310 .RS 4
2311 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
2312 \fB\-XX:+UseRTMDeopt\fR
2313 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\&.
2314 .RE
2315 .PP
2316 \-XX:RTMRetryCount=\fInumber_of_retries\fR
2317 .RS 4
2318 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
2319 \fB\-XX:UseRTMLocking\fR
2320 option must be enabled\&.
2321 .RE
2322 .PP
2323 \-XX:\-TieredCompilation
2324 .RS 4
2325 Disables the use of tiered compilation\&. By default, this option is enabled\&. Only the Java HotSpot Server VM supports this option\&.
2326 .RE
2327 .PP
2328 \-XX:+UseAES
2329 .RS 4
2330 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\&.
2331 .RE
2332 .PP
2333 \-XX:+UseAESIntrinsics
2334 .RS 4
2335 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
2336 \fB\-XX:\-UseAES \-XX:\-UseAESIntrinsics\fR\&. For example, to enable hardware AES, use the following flags:
2337 .sp
2338 .if n \{\
2339 .RS 4
2340 .\}
2341 .nf
2342 \fB\-XX:+UseAES \-XX:+UseAESIntrinsics\fR
2343
2344 .fi
2345 .if n \{\
2346 .RE
2347 .\}
2348 To support UseAES and UseAESIntrinsics flags for 32\-bit and 64\-bit use
2349 \fB\-server\fR
2350 option to choose Java HotSpot Server VM\&. These flags are not supported on Client VM\&.
2351 .RE
2352 .PP
2353 \-XX:+UseCodeCacheFlushing
2354 .RS 4
2355 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
2356 \fB\-XX:\-UseCodeCacheFlushing\fR\&.
2357 .RE
2358 .PP
2359 \-XX:+UseCondCardMark
2360 .RS 4
2361 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\&.
2362 .RE
2363 .PP
2364 \-XX:+UseRTMDeopt
2365 .RS 4
2366 Auto\-tunes RTM locking depending on the abort ratio\&. This ratio is specified by
2367 \fB\-XX:RTMAbortRatio\fR
2368 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
2369 \fB\-XX:+UseRTMLocking\fR
2370 option must be enabled\&.
2371 .RE
2372 .PP
2373 \-XX:+UseRTMLocking
2374 .RS 4
2375 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)\&.
2376 .sp
2377 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
2378 \fBXBEGIN\fR,
2379 \fBXABORT\fR,
2380 \fBXEND\fR, and
2381 \fBXTEST\fR\&. The
2382 \fBXBEGIN\fR
2383 and
2384 \fBXEND\fR
2385 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
2386 \fBXEND\fR
2387 instruction\&. The
2388 \fBXABORT\fR
2389 instruction can be used to explicitly abort a transaction and the
2390 \fBXEND\fR
2391 instruction to check if a set of instructions are being run in a transaction\&.
2392 .sp
2393 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\&.
2394 .sp
2395 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\&.
2396 .RE
2397 .PP
2398 \-XX:+UseSHA
2399 .RS 4
2400 Enables hardware\-based intrinsics for SHA crypto hash functions for SPARC hardware\&.
2401 \fBUseSHA\fR
2402 is used in conjunction with the
2403 \fBUseSHA1Intrinsics\fR,
2404 \fBUseSHA256Intrinsics\fR, and
2405 \fBUseSHA512Intrinsics\fR
2406 options\&.
2407 .sp
2408 The
2409 \fBUseSHA\fR
2410 and
2411 \fBUseSHA*Intrinsics\fR
2412 flags are enabled by default, and are supported only for Java HotSpot Server VM 64\-bit on SPARC T4 and newer\&.
2413 .sp
2414 This feature is only applicable when using the
2415 \fBsun\&.security\&.provider\&.Sun\fR
2416 provider for SHA operations\&.
2417 .sp
2418 To disable all hardware\-based SHA intrinsics, specify
2419 \fB\-XX:\-UseSHA\fR\&. To disable only a particular SHA intrinsic, use the appropriate corresponding option\&. For example:
2420 \fB\-XX:\-UseSHA256Intrinsics\fR\&.
2421 .RE
2422 .PP
2423 \-XX:+UseSHA1Intrinsics
2424 .RS 4
2425 Enables intrinsics for SHA\-1 crypto hash function\&.
2426 .RE
2427 .PP
2428 \-XX:+UseSHA256Intrinsics
2429 .RS 4
2430 Enables intrinsics for SHA\-224 and SHA\-256 crypto hash functions\&.
2431 .RE
2432 .PP
2433 \-XX:+UseSHA512Intrinsics
2434 .RS 4
2435 Enables intrinsics for SHA\-384 and SHA\-512 crypto hash functions\&.
2436 .RE
2437 .PP
2438 \-XX:+UseSuperWord
2439 .RS 4
2440 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
2441 \fB\-XX:\-UseSuperWord\fR\&. Only the Java HotSpot Server VM supports this option\&.
2442 .RE
2443 .SS "Advanced Serviceability Options"
2444 .PP
2445 These options provide the ability to gather system information and perform extensive debugging\&.
2446 .PP
2447 \-XX:+ExtendedDTraceProbes
2448 .RS 4
2449 Enables additional
2450 \fBdtrace\fR
2451 tool probes that impact the performance\&. By default, this option is disabled and
2452 \fBdtrace\fR
2453 performs only standard probes\&.
2454 .RE
2455 .PP
2456 \-XX:+HeapDumpOnOutOfMemory
2457 .RS 4
2458 Enables the dumping of the Java heap to a file in the current directory by using the heap profiler (HPROF) when a
2459 \fBjava\&.lang\&.OutOfMemoryError\fR
2460 exception is thrown\&. You can explicitly set the heap dump file path and name using the
2461 \fB\-XX:HeapDumpPath\fR
2462 option\&. By default, this option is disabled and the heap is not dumped when an
2463 \fBOutOfMemoryError\fR
2464 exception is thrown\&.
2465 .RE
2466 .PP
2467 \-XX:HeapDumpPath=\fIpath\fR
2468 .RS 4
2469 Sets the path and file name for writing the heap dump provided by the heap profiler (HPROF) when the
2470 \fB\-XX:+HeapDumpOnOutOfMemoryError\fR
2471 option is set\&. By default, the file is created in the current working directory, and it is named
2472 \fBjava_pid\fR\fIpid\fR\fB\&.hprof\fR
2473 where
2474 \fIpid\fR
2475 is the identifier of the process that caused the error\&. The following example shows how to set the default file explicitly (\fB%p\fR
2476 represents the current process identificator):
2477 .sp
2478 .if n \{\
2479 .RS 4
2480 .\}
2481 .nf
2482 \fB\-XX:HeapDumpPath=\&./java_pid%p\&.hprof\fR
2483
2484 .fi
2485 .if n \{\
2486 .RE
2487 .\}
2488 The following example shows how to set the heap dump file to
2489 \fB/var/log/java/java_heapdump\&.hprof\fR:
2490 .sp
2491 .if n \{\
2492 .RS 4
2493 .\}
2494 .nf
2495 \fB\-XX:HeapDumpPath=/var/log/java/java_heapdump\&.hprof\fR
2496
2497 .fi
2498 .if n \{\
2499 .RE
2500 .\}
2501 .RE
2502 .PP
2503 \-XX:LogFile=\fIpath\fR
2504 .RS 4
2505 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
2506 \fBhotspot\&.log\fR\&.
2507 .sp
2508 The following example shows how to set the log file to
2509 \fB/var/log/java/hotspot\&.log\fR:
2510 .sp
2511 .if n \{\
2512 .RS 4
2513 .\}
2514 .nf
2515 \fB\-XX:LogFile=/var/log/java/hotspot\&.log\fR
2516
2517 .fi
2518 .if n \{\
2519 .RE
2520 .\}
2521 .RE
2522 .PP
2523 \-XX:+PrintClassHistogram
2524 .RS 4
2525 Enables printing of a class instance histogram after a
2526 \fBControl+C\fR
2527 event (\fBSIGTERM\fR)\&. By default, this option is disabled\&.
2528 .sp
2529 Setting this option is equivalent to running the
2530 \fBjmap \-histo\fR
2531 command, or the
2532 \fBjcmd \fR\fIpid\fR\fB GC\&.class_histogram\fR
2533 command, where
2534 \fIpid\fR
2535 is the current Java process identifier\&.
2536 .RE
2537 .PP
2538 \-XX:+PrintConcurrentLocks
2539 .RS 4
2540 Enables printing of locks after a event\&. By default, this option is disabled\&.
2541 .sp
2542 Enables printing of
2543 \fBjava\&.util\&.concurrent\fR
2544 locks after a
2545 \fBControl+C\fR
2546 event (\fBSIGTERM\fR)\&. By default, this option is disabled\&.
2547 .sp
2548 Setting this option is equivalent to running the
2549 \fBjstack \-l\fR
2550 command or the
2551 \fBjcmd \fR\fIpid\fR\fB Thread\&.print \-l\fR
2552 command, where
2553 \fIpid\fR
2554 is the current Java process identifier\&.
2555 .RE
2556 .PP
2557 \-XX:+UnlockDiagnosticVMOptions
2558 .RS 4
2559 Unlocks the options intended for diagnosing the JVM\&. By default, this option is disabled and diagnostic options are not available\&.
2560 .RE
2561 .SS "Advanced Garbage Collection Options"
2562 .PP
2563 These options control how garbage collection (GC) is performed by the Java HotSpot VM\&.
2564 .PP
2565 \-XX:+AggressiveHeap
2566 .RS 4
2567 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\&.
2568 .RE
2569 .PP
2570 \-XX:+AlwaysPreTouch
2571 .RS 4
2572 Enables touching of every page on the Java heap during JVM initialization\&. This gets all pages into the memory before entering the
2573 \fBmain()\fR
2574 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\&.
2575 .RE
2576 .PP
2577 \-XX:+CMSClassUnloadingEnabled
2578 .RS 4
2579 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
2580 \fB\-XX:\-CMSClassUnloadingEnabled\fR\&.
2581 .RE
2582 .PP
2583 \-XX:CMSExpAvgFactor=\fIpercent\fR
2584 .RS 4
2585 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%:
2586 .sp
2587 .if n \{\
2588 .RS 4
2589 .\}
2590 .nf
2591 \fB\-XX:CMSExpAvgFactor=15\fR
2592
2593 .fi
2594 .if n \{\
2595 .RE
2596 .\}
2597 .RE
2598 .PP
2599 \-XX:CMSInitiatingOccupancyFraction=\fIpercent\fR
2600 .RS 4
2601 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
2602 \fB\-XX:CMSTriggerRatio\fR
2603 is used to define the value of the initiating occupancy fraction\&.
2604 .sp
2605 The following example shows how to set the occupancy fraction to 20%:
2606 .sp
2607 .if n \{\
2608 .RS 4
2609 .\}
2610 .nf
2611 \fB\-XX:CMSInitiatingOccupancyFraction=20\fR
2612
2613 .fi
2614 .if n \{\
2615 .RE
2616 .\}
2617 .RE
2618 .PP
2619 \-XX:+CMSScavengeBeforeRemark
2620 .RS 4
2621 Enables scavenging attempts before the CMS remark step\&. By default, this option is disabled\&.
2622 .RE
2623 .PP
2624 \-XX:CMSTriggerRatio=\fIpercent\fR
2625 .RS 4
2626 Sets the percentage (0 to 100) of the value specified by
2627 \fB\-XX:MinHeapFreeRatio\fR
2628 that is allocated before a CMS collection cycle commences\&. The default value is set to 80%\&.
2629 .sp
2630 The following example shows how to set the occupancy fraction to 75%:
2631 .sp
2632 .if n \{\
2633 .RS 4
2634 .\}
2635 .nf
2636 \fB\-XX:CMSTriggerRatio=75\fR
2637
2638 .fi
2639 .if n \{\
2640 .RE
2641 .\}
2642 .RE
2643 .PP
2644 \-XX:ConcGCThreads=\fIthreads\fR
2645 .RS 4
2646 Sets the number of threads used for concurrent GC\&. The default value depends on the number of CPUs available to the JVM\&.
2647 .sp
2648 For example, to set the number of threads for concurrent GC to 2, specify the following option:
2649 .sp
2650 .if n \{\
2651 .RS 4
2652 .\}
2653 .nf
2654 \fB\-XX:ConcGCThreads=2\fR
2655
2656 .fi
2657 .if n \{\
2658 .RE
2659 .\}
2660 .RE
2661 .PP
2662 \-XX:+DisableExplicitGC
2663 .RS 4
2664 Enables the option that disables processing of calls to
2665 \fBSystem\&.gc()\fR\&. This option is disabled by default, meaning that calls to
2666 \fBSystem\&.gc()\fR
2667 are processed\&. If processing of calls to
2668 \fBSystem\&.gc()\fR
2669 is disabled, the JVM still performs GC when necessary\&.
2670 .RE
2671 .PP
2672 \-XX:+ExplicitGCInvokesConcurrent
2673 .RS 4
2674 Enables invoking of concurrent GC by using the
2675 \fBSystem\&.gc()\fR
2676 request\&. This option is disabled by default and can be enabled only together with the
2677 \fB\-XX:+UseConcMarkSweepGC\fR
2678 option\&.
2679 .RE
2680 .PP
2681 \-XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses
2682 .RS 4
2683 Enables invoking of concurrent GC by using the
2684 \fBSystem\&.gc()\fR
2685 request and unloading of classes during the concurrent GC cycle\&. This option is disabled by default and can be enabled only together with the
2686 \fB\-XX:+UseConcMarkSweepGC\fR
2687 option\&.
2688 .RE
2689 .PP
2690 \-XX:G1HeapRegionSize=\fIsize\fR
2691 .RS 4
2692 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\&.
2693 .sp
2694 The following example shows how to set the size of the subdivisions to 16 MB:
2695 .sp
2696 .if n \{\
2697 .RS 4
2698 .\}
2699 .nf
2700 \fB\-XX:G1HeapRegionSize=16m\fR
2701
2702 .fi
2703 .if n \{\
2704 .RE
2705 .\}
2706 .RE
2707 .PP
2708 \-XX:+G1PrintHeapRegions
2709 .RS 4
2710 Enables the printing of information about which regions are allocated and which are reclaimed by the G1 collector\&. By default, this option is disabled\&.
2711 .RE
2712 .PP
2713 \-XX:G1ReservePercent=\fIpercent\fR
2714 .RS 4
2715 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%\&.
2716 .sp
2717 The following example shows how to set the reserved heap to 20%:
2718 .sp
2719 .if n \{\
2720 .RS 4
2721 .\}
2722 .nf
2723 \fB\-XX:G1ReservePercent=20\fR
2724
2725 .fi
2726 .if n \{\
2727 .RE
2728 .\}
2729 .RE
2730 .PP
2731 \-XX:InitialHeapSize=\fIsize\fR
2732 .RS 4
2733 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
2734 \fBk\fR
2735 or
2736 \fBK\fR
2737 to indicate kilobytes,
2738 \fBm\fR
2739 or
2740 \fBM\fR
2741 to indicate megabytes,
2742 \fBg\fR
2743 or
2744 \fBG\fR
2745 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. See the section "Ergonomics" in
2746 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
2747 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
2748 .sp
2749 The following examples show how to set the size of allocated memory to 6 MB using various units:
2750 .sp
2751 .if n \{\
2752 .RS 4
2753 .\}
2754 .nf
2755 \fB\-XX:InitialHeapSize=6291456\fR
2756 \fB\-XX:InitialHeapSize=6144k\fR
2757 \fB\-XX:InitialHeapSize=6m\fR
2758
2759 .fi
2760 .if n \{\
2761 .RE
2762 .\}
2763 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
2764 \fB\-XX:NewSize\fR
2765 option\&.
2766 .RE
2767 .PP
2768 \-XX:InitialSurvivorRatio=\fIratio\fR
2769 .RS 4
2770 Sets the initial survivor space ratio used by the throughput garbage collector (which is enabled by the
2771 \fB\-XX:+UseParallelGC\fR
2772 and/or \-\fBXX:+UseParallelOldGC\fR
2773 options)\&. Adaptive sizing is enabled by default with the throughput garbage collector by using the
2774 \fB\-XX:+UseParallelGC\fR
2775 and
2776 \fB\-XX:+UseParallelOldGC\fR
2777 options, and survivor space is resized according to the application behavior, starting with the initial value\&. If adaptive sizing is disabled (using the
2778 \fB\-XX:\-UseAdaptiveSizePolicy\fR
2779 option), then the
2780 \fB\-XX:SurvivorRatio\fR
2781 option should be used to set the size of the survivor space for the entire execution of the application\&.
2782 .sp
2783 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):
2784 .sp
2785 .if n \{\
2786 .RS 4
2787 .\}
2788 .nf
2789 \fBS=Y/(R+2)\fR
2790
2791 .fi
2792 .if n \{\
2793 .RE
2794 .\}
2795 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\&.
2796 .sp
2797 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\&.
2798 .sp
2799 The following example shows how to set the initial survivor space ratio to 4:
2800 .sp
2801 .if n \{\
2802 .RS 4
2803 .\}
2804 .nf
2805 \fB\-XX:InitialSurvivorRatio=4\fR
2806
2807 .fi
2808 .if n \{\
2809 .RE
2810 .\}
2811 .RE
2812 .PP
2813 \-XX:InitiatingHeapOccupancyPercent=\fIpercent\fR
2814 .RS 4
2815 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)\&.
2816 .sp
2817 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%:
2818 .sp
2819 .if n \{\
2820 .RS 4
2821 .\}
2822 .nf
2823 \fB\-XX:InitiatingHeapOccupancyPercent=75\fR
2824
2825 .fi
2826 .if n \{\
2827 .RE
2828 .\}
2829 .RE
2830 .PP
2831 \-XX:MaxGCPauseMillis=\fItime\fR
2832 .RS 4
2833 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\&.
2834 .sp
2835 The following example shows how to set the maximum target pause time to 500 ms:
2836 .sp
2837 .if n \{\
2838 .RS 4
2839 .\}
2840 .nf
2841 \fB\-XX:MaxGCPauseMillis=500\fR
2842
2843 .fi
2844 .if n \{\
2845 .RE
2846 .\}
2847 .RE
2848 .PP
2849 \-XX:MaxHeapSize=\fIsize\fR
2850 .RS 4
2851 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
2852 \fBk\fR
2853 or
2854 \fBK\fR
2855 to indicate kilobytes,
2856 \fBm\fR
2857 or
2858 \fBM\fR
2859 to indicate megabytes,
2860 \fBg\fR
2861 or
2862 \fBG\fR
2863 to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. For server deployments,
2864 \fB\-XX:InitialHeapSize\fR
2865 and
2866 \fB\-XX:MaxHeapSize\fR
2867 are often set to the same value\&. See the section "Ergonomics" in
2868 \fIJava SE HotSpot Virtual Machine Garbage Collection Tuning Guide\fR
2869 at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gctuning/index\&.html\&.
2870 .sp
2871 The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:
2872 .sp
2873 .if n \{\
2874 .RS 4
2875 .\}
2876 .nf
2877 \fB\-XX:MaxHeapSize=83886080\fR
2878 \fB\-XX:MaxHeapSize=81920k\fR
2879 \fB\-XX:MaxHeapSize=80m\fR
2880
2881 .fi
2882 .if n \{\
2883 .RE
2884 .\}
2885 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\&.
2886 .sp
2887 The
2888 \fB\-XX:MaxHeapSize\fR
2889 option is equivalent to
2890 \fB\-Xmx\fR\&.
2891 .RE
2892 .PP
2893 \-XX:MaxHeapFreeRatio=\fIpercent\fR
2894 .RS 4
2895 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%\&.
2896 .sp
2897 The following example shows how to set the maximum free heap ratio to 75%:
2898 .sp
2899 .if n \{\
2900 .RS 4
2901 .\}
2902 .nf
2903 \fB\-XX:MaxHeapFreeRatio=75\fR
2904
2905 .fi
2906 .if n \{\
2907 .RE
2908 .\}
2909 .RE
2910 .PP
2911 \-XX:MaxMetaspaceSize=\fIsize\fR
2912 .RS 4
2913 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\&.
2914 .sp
2915 The following example shows how to set the maximum class metadata size to 256 MB:
2916 .sp
2917 .if n \{\
2918 .RS 4
2919 .\}
2920 .nf
2921 \fB\-XX:MaxMetaspaceSize=256m\fR
2922
2923 .fi
2924 .if n \{\
2925 .RE
2926 .\}
2927 .RE
2928 .PP
2929 \-XX:MaxNewSize=\fIsize\fR
2930 .RS 4
2931 Sets the maximum size (in bytes) of the heap for the young generation (nursery)\&. The default value is set ergonomically\&.
2932 .RE
2933 .PP
2934 \-XX:MaxTenuringThreshold=\fIthreshold\fR
2935 .RS 4
2936 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\&.
2937 .sp
2938 The following example shows how to set the maximum tenuring threshold to 10:
2939 .sp
2940 .if n \{\
2941 .RS 4
2942 .\}
2943 .nf
2944 \fB\-XX:MaxTenuringThreshold=10\fR
2945
2946 .fi
2947 .if n \{\
2948 .RE
2949 .\}
2950 .RE
2951 .PP
2952 \-XX:MetaspaceSize=\fIsize\fR
2953 .RS 4
2954 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\&.
2955 .RE
2956 .PP
2957 \-XX:MinHeapFreeRatio=\fIpercent\fR
2958 .RS 4
2959 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%\&.
2960 .sp
2961 The following example shows how to set the minimum free heap ratio to 25%:
2962 .sp
2963 .if n \{\
2964 .RS 4
2965 .\}
2966 .nf
2967 \fB\-XX:MinHeapFreeRatio=25\fR
2968
2969 .fi
2970 .if n \{\
2971 .RE
2972 .\}
2973 .RE
2974 .PP
2975 \-XX:NewRatio=\fIratio\fR
2976 .RS 4
2977 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:
2978 .sp
2979 .if n \{\
2980 .RS 4
2981 .\}
2982 .nf
2983 \fB\-XX:NewRatio=1\fR
2984
2985 .fi
2986 .if n \{\
2987 .RE
2988 .\}
2989 .RE
2990 .PP
2991 \-XX:NewSize=\fIsize\fR
2992 .RS 4
2993 Sets the initial size (in bytes) of the heap for the young generation (nursery)\&. Append the letter
2994 \fBk\fR
2995 or
2996 \fBK\fR
2997 to indicate kilobytes,
2998 \fBm\fR
2999 or
3000 \fBM\fR
3001 to indicate megabytes,
3002 \fBg\fR
3003 or
3004 \fBG\fR
3005 to indicate gigabytes\&.
3006 .sp
3007 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\&.
3008 .sp
3009 The following examples show how to set the initial size of young generation to 256 MB using various units:
3010 .sp
3011 .if n \{\
3012 .RS 4
3013 .\}
3014 .nf
3015 \fB\-XX:NewSize=256m\fR
3016 \fB\-XX:NewSize=262144k\fR
3017 \fB\-XX:NewSize=268435456\fR
3018
3019 .fi
3020 .if n \{\
3021 .RE
3022 .\}
3023 The
3024 \fB\-XX:NewSize\fR
3025 option is equivalent to
3026 \fB\-Xmn\fR\&.
3027 .RE
3028 .PP
3029 \-XX:ParallelGCThreads=\fIthreads\fR
3030 .RS 4
3031 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\&.
3032 .sp
3033 For example, to set the number of threads for parallel GC to 2, specify the following option:
3034 .sp
3035 .if n \{\
3036 .RS 4
3037 .\}
3038 .nf
3039 \fB\-XX:ParallelGCThreads=2\fR
3040
3041 .fi
3042 .if n \{\
3043 .RE
3044 .\}
3045 .RE
3046 .PP
3047 \-XX:+ParallelRefProcEnabled
3048 .RS 4
3049 Enables parallel reference processing\&. By default, this option is disabled\&.
3050 .RE
3051 .PP
3052 \-XX:+PrintAdaptiveSizePolicy
3053 .RS 4
3054 Enables printing of information about adaptive generation sizing\&. By default, this option is disabled\&.
3055 .RE
3056 .PP
3057 \-XX:+PrintGC
3058 .RS 4
3059 Enables printing of messages at every GC\&. By default, this option is disabled\&.
3060 .RE
3061 .PP
3062 \-XX:+PrintGCApplicationConcurrentTime
3063 .RS 4
3064 Enables printing of how much time elapsed since the last pause (for example, a GC pause)\&. By default, this option is disabled\&.
3065 .RE
3066 .PP
3067 \-XX:+PrintGCApplicationStoppedTime
3068 .RS 4
3069 Enables printing of how much time the pause (for example, a GC pause) lasted\&. By default, this option is disabled\&.
3070 .RE
3071 .PP
3072 \-XX:+PrintGCDateStamps
3073 .RS 4
3074 Enables printing of a date stamp at every GC\&. By default, this option is disabled\&.
3075 .RE
3076 .PP
3077 \-XX:+PrintGCDetails
3078 .RS 4
3079 Enables printing of detailed messages at every GC\&. By default, this option is disabled\&.
3080 .RE
3081 .PP
3082 \-XX:+PrintGCTaskTimeStamps
3083 .RS 4
3084 Enables printing of time stamps for every individual GC worker thread task\&. By default, this option is disabled\&.
3085 .RE
3086 .PP
3087 \-XX:+PrintGCTimeStamps
3088 .RS 4
3089 Enables printing of time stamps at every GC\&. By default, this option is disabled\&.
3090 .RE
3091 .PP
3092 \-XX:+PrintStringDeduplicationStatistics
3093 .RS 4
3094 Prints detailed deduplication statistics\&. By default, this option is disabled\&. See the
3095 \fB\-XX:+UseStringDeduplication\fR
3096 option\&.
3097 .RE
3098 .PP
3099 \-XX:+PrintTenuringDistribution
3100 .RS 4
3101 Enables printing of tenuring age information\&. The following is an example of the output:
3102 .sp
3103 .if n \{\
3104 .RS 4
3105 .\}
3106 .nf
3107 \fBDesired survivor size 48286924 bytes, new threshold 10 (max 10)\fR
3108 \fB\- age 1: 28992024 bytes, 28992024 total\fR
3109 \fB\- age 2: 1366864 bytes, 30358888 total\fR
3110 \fB\- age 3: 1425912 bytes, 31784800 total\fR
3111 \fB\&.\&.\&.\fR
3112
3113 .fi
3114 .if n \{\
3115 .RE
3116 .\}
3117 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\&.
3118 .sp
3119 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\&.
3120 .sp
3121 By default, this option is disabled\&.
3122 .RE
3123 .PP
3124 \-XX:+ScavengeBeforeFullGC
3125 .RS 4
3126 Enables GC of the young generation before each full GC\&. This option is enabled by default\&. Oracle recommends that you
3127 \fIdo not\fR
3128 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
3129 \fB\-XX:\-ScavengeBeforeFullGC\fR\&.
3130 .RE
3131 .PP
3132 \-XX:SoftRefLRUPolicyMSPerMB=\fItime\fR
3133 .RS 4
3134 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
3135 \fB\-XX:SoftRefLRUPolicyMSPerMB\fR
3136 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
3137 \fB\-Xmx\fR
3138 option has a significant effect on how quickly soft references are garbage collected\&.
3139 .sp
3140 The following example shows how to set the value to 2\&.5 seconds:
3141 .sp
3142 .if n \{\
3143 .RS 4
3144 .\}
3145 .nf
3146 \fB\-XX:SoftRefLRUPolicyMSPerMB=2500\fR
3147
3148 .fi
3149 .if n \{\
3150 .RE
3151 .\}
3152 .RE
3153 .PP
3154 \-XX:StringDeduplicationAgeThreshold=\fIthreshold\fR
3155 .RS 4
3156 \fBString\fR
3157 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
3158 \fB\-XX:+PrintTenuringDistribution\fR
3159 option\&. Note that
3160 \fBString\fR
3161 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
3162 \fB3\fR\&. See the
3163 \fB\-XX:+UseStringDeduplication\fR
3164 option\&.
3165 .RE
3166 .PP
3167 \-XX:SurvivorRatio=\fIratio\fR
3168 .RS 4
3169 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:
3170 .sp
3171 .if n \{\
3172 .RS 4
3173 .\}
3174 .nf
3175 \fB\-XX:SurvivorRatio=4\fR
3176
3177 .fi
3178 .if n \{\
3179 .RE
3180 .\}
3181 .RE
3182 .PP
3183 \-XX:TargetSurvivorRatio=\fIpercent\fR
3184 .RS 4
3185 Sets the desired percentage of survivor space (0 to 100) used after young garbage collection\&. By default, this option is set to 50%\&.
3186 .sp
3187 The following example shows how to set the target survivor space ratio to 30%:
3188 .sp
3189 .if n \{\
3190 .RS 4
3191 .\}
3192 .nf
3193 \fB\-XX:TargetSurvivorRatio=30\fR
3194
3195 .fi
3196 .if n \{\
3197 .RE
3198 .\}
3199 .RE
3200 .PP
3201 \-XX:TLABSize=\fIsize\fR
3202 .RS 4
3203 Sets the initial size (in bytes) of a thread\-local allocation buffer (TLAB)\&. Append the letter
3204 \fBk\fR
3205 or
3206 \fBK\fR
3207 to indicate kilobytes,
3208 \fBm\fR
3209 or
3210 \fBM\fR
3211 to indicate megabytes,
3212 \fBg\fR
3213 or
3214 \fBG\fR
3215 to indicate gigabytes\&. If this option is set to 0, then the JVM chooses the initial size automatically\&.
3216 .sp
3217 The following example shows how to set the initial TLAB size to 512 KB:
3218 .sp
3219 .if n \{\
3220 .RS 4
3221 .\}
3222 .nf
3223 \fB\-XX:TLABSize=512k\fR
3224
3225 .fi
3226 .if n \{\
3227 .RE
3228 .\}
3229 .RE
3230 .PP
3231 \-XX:+UseAdaptiveSizePolicy
3232 .RS 4
3233 Enables the use of adaptive generation sizing\&. This option is enabled by default\&. To disable adaptive generation sizing, specify
3234 \fB\-XX:\-UseAdaptiveSizePolicy\fR
3235 and set the size of the memory allocation pool explicitly (see the
3236 \fB\-XX:SurvivorRatio\fR
3237 option)\&.
3238 .RE
3239 .PP
3240 \-XX:+UseCMSInitiatingOccupancyOnly
3241 .RS 4
3242 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\&.
3243 .RE
3244 .PP
3245 \-XX:+UseConcMarkSweepGC
3246 .RS 4
3247 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\&.
3248 .sp
3249 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
3250 \fB\-XX:+UseParNewGC\fR
3251 option is automatically set and you should not disable it, because the following combination of options has been deprecated in JDK 8:
3252 \fB\-XX:+UseConcMarkSweepGC \-XX:\-UseParNewGC\fR\&.
3253 .RE
3254 .PP
3255 \-XX:+UseG1GC
3256 .RS 4
3257 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)\&.
3258 .sp
3259 By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM\&.
3260 .RE
3261 .PP
3262 \-XX:+UseGCOverheadLimit
3263 .RS 4
3264 Enables the use of a policy that limits the proportion of time spent by the JVM on GC before an
3265 \fBOutOfMemoryError\fR
3266 exception is thrown\&. This option is enabled, by default and the parallel GC will throw an
3267 \fBOutOfMemoryError\fR
3268 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
3269 \fB\-XX:\-UseGCOverheadLimit\fR\&.
3270 .RE
3271 .PP
3272 \-XX:+UseNUMA
3273 .RS 4
3274 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)\&.
3275 .RE
3276 .PP
3277 \-XX:+UseParallelGC
3278 .RS 4
3279 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\&.
3280 .sp
3281 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
3282 \fB\-XX:+UseParallelOldGC\fR
3283 option is automatically enabled, unless you explicitly disable it\&.
3284 .RE
3285 .PP
3286 \-XX:+UseParallelOldGC
3287 .RS 4
3288 Enables the use of the parallel garbage collector for full GCs\&. By default, this option is disabled\&. Enabling it automatically enables the
3289 \fB\-XX:+UseParallelGC\fR
3290 option\&.
3291 .RE
3292 .PP
3293 \-XX:+UseParNewGC
3294 .RS 4
3295 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
3296 \fB\-XX:+UseConcMarkSweepGC\fR
3297 option\&. Using the
3298 \fB\-XX:+UseParNewGC\fR
3299 option without the
3300 \fB\-XX:+UseConcMarkSweepGC\fR
3301 option was deprecated in JDK 8\&.
3302 .RE
3303 .PP
3304 \-XX:+UseSerialGC
3305 .RS 4
3306 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\&.
3307 .RE
3308 .PP
3309 \-XX:+UseSHM
3310 .RS 4
3311 On Linux, enables the JVM to use shared memory to setup large pages\&.
3312 .sp
3313 For more information, see "Large Pages"\&.
3314 .RE
3315 .PP
3316 \-XX:+UseStringDeduplication
3317 .RS 4
3318 Enables string deduplication\&. By default, this option is disabled\&. To use this option, you must enable the garbage\-first (G1) garbage collector\&. See the
3319 \fB\-XX:+UseG1GC\fR
3320 option\&.
3321 .sp
3322 \fIString deduplication\fR
3323 reduces the memory footprint of
3324 \fBString\fR
3325 objects on the Java heap by taking advantage of the fact that many
3326 \fBString\fR
3327 objects are identical\&. Instead of each
3328 \fBString\fR
3329 object pointing to its own character array, identical
3330 \fBString\fR
3331 objects can point to and share the same character array\&.
3332 .RE
3333 .PP
3334 \-XX:+UseTLAB
3335 .RS 4
3336 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
3337 \fB\-XX:\-UseTLAB\fR\&.
3338 .RE
3339 .SS "Deprecated and Removed Options"
3340 .PP
3341 These options were included in the previous release, but have since been considered unnecessary\&.
3342 .PP
3343 \-Xincgc
3344 .RS 4
3345 Enables incremental garbage collection\&. This option was deprecated in JDK 8 with no replacement\&.
3346 .RE
3347 .PP
3348 \-Xrun\fIlibname\fR
3349 .RS 4
3350 Loads the specified debugging/profiling library\&. This option was superseded by the
3351 \fB\-agentlib\fR
3352 option\&.
3353 .RE
3354 .PP
3355 \-XX:CMSIncrementalDutyCycle=\fIpercent\fR
3356 .RS 4
3357 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
3358 \fB\-XX:+CMSIncrementalMode\fR
3359 option\&.
3360 .RE
3361 .PP
3362 \-XX:CMSIncrementalDutyCycleMin=\fIpercent\fR
3363 .RS 4
3364 Sets the percentage of time (0 to 100) between minor collections that is the lower bound for the duty cycle when
3365 \fB\-XX:+CMSIncrementalPacing\fR
3366 is enabled\&. This option was deprecated in JDK 8 with no replacement, following the deprecation of the
3367 \fB\-XX:+CMSIncrementalMode\fR
3368 option\&.
3369 .RE
3370 .PP
3371 \-XX:+CMSIncrementalMode
3372 .RS 4
3373 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
3374 \fBCMSIncremental\fR\&.
3375 .RE
3376 .PP
3377 \-XX:CMSIncrementalOffset=\fIpercent\fR
3378 .RS 4
3379 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
3380 \fB\-XX:+CMSIncrementalMode\fR
3381 option\&.
3382 .RE
3383 .PP
3384 \-XX:+CMSIncrementalPacing
3385 .RS 4
3386 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
3387 \fB\-XX:+CMSIncrementalMode\fR
3388 option\&.
3389 .RE
3390 .PP
3391 \-XX:CMSIncrementalSafetyFactor=\fIpercent\fR
3392 .RS 4
3393 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
3394 \fB\-XX:+CMSIncrementalMode\fR
3395 option\&.
3396 .RE
3397 .PP
3398 \-XX:CMSInitiatingPermOccupancyFraction=\fIpercent\fR
3399 .RS 4
3400 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\&.
3401 .RE
3402 .PP
3403 \-XX:MaxPermSize=\fIsize\fR
3404 .RS 4
3405 Sets the maximum permanent generation space size (in bytes)\&. This option was deprecated in JDK 8, and superseded by the
3406 \fB\-XX:MaxMetaspaceSize\fR
3407 option\&.
3408 .RE
3409 .PP
3410 \-XX:PermSize=\fIsize\fR
3411 .RS 4
3412 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
3413 \fB\-XX:MetaspaceSize\fR
3414 option\&.
3415 .RE
3416 .PP
3417 \-XX:+UseSplitVerifier
3418 .RS 4
3419 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\&.
3420 .RE
3421 .PP
3422 \-XX:+UseStringCache
3423 .RS 4
3424 Enables caching of commonly allocated strings\&. This option was removed from JDK 8 with no replacement\&.
3425 .RE
3426 .SH "PERFORMANCE TUNING EXAMPLES"
3427 .PP
3428 The following examples show how to use experimental tuning flags to either optimize throughput or to provide lower response time\&.
3429 .PP
3430 \fBExample 1 \fRTuning for Higher Throughput
3431 .RS 4
3432 .sp
3433 .if n \{\
3434 .RS 4
3435 .\}
3436 .nf
3437 \fBjava \-d64 \-server \-XX:+UseLargePages \-Xmn10g \-Xms26g \-Xmx26g\fR
3438
3439 .fi
3440 .if n \{\
3441 .RE
3442 .\}
3443 .RE
3444 .PP
3445 \fBExample 2 \fRTuning for Lower Response Time
3446 .RS 4
3447 .sp
3448 .if n \{\
3449 .RS 4
3450 .\}
3451 .nf
3452 \fBjava \-d64 \-XX:+UseG1GC \-Xms26g Xmx26g \-XX:MaxGCPauseMillis=500 \-XX:+PrintGCTimeStamp\fR
3453
3454 .fi
3455 .if n \{\
3456 .RE
3457 .\}
3458 .RE
3459 .SH "LARGE PAGES"
3460 .PP
3461 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\&.
3462 .PP
3463 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\&.
3464 .PP
3465 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\&.
3466 .SS "Large Pages Support"
3467 .PP
3468 Solaris and Linux support large pages\&.
3469 .sp
3470 .it 1 an-trap
3471 .nr an-no-space-flag 1
3472 .nr an-break-flag 1
3473 .br
3474 .ps +1
3475 \fBSolaris\fR
3476 .RS 4
3477 .PP
3478 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\&.
3479 .RE
3480 .sp
3481 .it 1 an-trap
3482 .nr an-no-space-flag 1
3483 .nr an-break-flag 1
3484 .br
3485 .ps +1
3486 \fBLinux\fR
3487 .RS 4
3488 .PP
3489 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:
3490 .sp
3491 .if n \{\
3492 .RS 4
3493 .\}
3494 .nf
3495 \fB# cat /proc/meminfo | grep Huge\fR
3496 \fBHugePages_Total: 0\fR
3497 \fBHugePages_Free: 0\fR
3498 \fBHugepagesize: 2048 kB\fR
3499
3500 .fi
3501 .if n \{\
3502 .RE
3503 .\}
3504 .PP
3505 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
3506 \fBroot\fR, and then follow these steps:
3507 .sp
3508 .RS 4
3509 .ie n \{\
3510 \h'-04' 1.\h'+01'\c
3511 .\}
3512 .el \{\
3513 .sp -1
3514 .IP " 1." 4.2
3515 .\}
3516 If you are using the option
3517 \fB\-XX:+UseSHM\fR
3518 (instead of
3519 \fB\-XX:+UseHugeTLBFS\fR), then increase the
3520 \fBSHMMAX\fR
3521 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:
3522 .sp
3523 .if n \{\
3524 .RS 4
3525 .\}
3526 .nf
3527 \fB# echo 4294967295 > /proc/sys/kernel/shmmax\fR
3528
3529 .fi
3530 .if n \{\
3531 .RE
3532 .\}
3533 .RE
3534 .sp
3535 .RS 4
3536 .ie n \{\
3537 \h'-04' 2.\h'+01'\c
3538 .\}
3539 .el \{\
3540 .sp -1
3541 .IP " 2." 4.2
3542 .\}
3543 If you are using the option
3544 \fB\-XX:+UseSHM\fR
3545 or
3546 \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):
3547 .sp
3548 .if n \{\
3549 .RS 4
3550 .\}
3551 .nf
3552 \fB# echo 1536 > /proc/sys/vm/nr_hugepages\fR
3553
3554 .fi
3555 .if n \{\
3556 .RE
3557 .\}
3558 .RE
3559 .if n \{\
3560 .sp
3561 .\}
3562 .RS 4
3563 .it 1 an-trap
3564 .nr an-no-space-flag 1
3565 .nr an-break-flag 1
3566 .br
3567 .ps +1
3568 \fBNote\fR
3569 .ps -1
3570 .br
3571 .TS
3572 allbox tab(:);
3573 l.
3574 T{
3575 .sp
3576 .RS 4
3577 .ie n \{\
3578 \h'-04'\(bu\h'+03'\c
3579 .\}
3580 .el \{\
3581 .sp -1
3582 .IP \(bu 2.3
3583 .\}
3584 Note that the values contained in
3585 \fB/proc\fR
3586 will reset after you reboot your system, so may want to set them in an initialization script (for example,
3587 \fBrc\&.local\fR
3588 or
3589 \fBsysctl\&.conf\fR)\&.
3590 .RE
3591 .sp
3592 .RS 4
3593 .ie n \{\
3594 \h'-04'\(bu\h'+03'\c
3595 .\}
3596 .el \{\
3597 .sp -1
3598 .IP \(bu 2.3
3599 .\}
3600 If you configure (or resize) the OS kernel parameters
3601 \fB/proc/sys/kernel/shmmax\fR
3602 or
3603 \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:
3604 .sp
3605 .RS 4
3606 .ie n \{\
3607 \h'-04'\(bu\h'+03'\c
3608 .\}
3609 .el \{\
3610 .sp -1
3611 .IP \(bu 2.3
3612 .\}
3613 Java heap
3614 .RE
3615 .sp
3616 .RS 4
3617 .ie n \{\
3618 \h'-04'\(bu\h'+03'\c
3619 .\}
3620 .el \{\
3621 .sp -1
3622 .IP \(bu 2.3
3623 .\}
3624 Code cache
3625 .RE
3626 .sp
3627 .RS 4
3628 .ie n \{\
3629 \h'-04'\(bu\h'+03'\c
3630 .\}
3631 .el \{\
3632 .sp -1
3633 .IP \(bu 2.3
3634 .\}
3635 The marking bitmap data structure for the parallel GC
3636 .RE
3637 .sp
3638 Consequently, if you configure the
3639 \fBnr_hugepages\fR
3640 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\&.
3641 .RE
3642 T}
3643 .TE
3644 .sp 1
3645 .sp .5v
3646 .RE
3647 .RE
3648 .SH "EXIT STATUS"
3649 .PP
3650 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
3651 \fBSystem\&.exit(exitValue)\fR\&. The values are:
3652 .sp
3653 .RS 4
3654 .ie n \{\
3655 \h'-04'\(bu\h'+03'\c
3656 .\}
3657 .el \{\
3658 .sp -1
3659 .IP \(bu 2.3
3660 .\}
3661 \fB0\fR: Successful completion
3662 .RE
3663 .sp
3664 .RS 4
3665 .ie n \{\
3666 \h'-04'\(bu\h'+03'\c
3667 .\}
3668 .el \{\
3669 .sp -1
3670 .IP \(bu 2.3
3671 .\}
3672 \fB>0\fR: An error occurred
3673 .RE
3674 .SH "SEE ALSO"
3675 .sp
3676 .RS 4
3677 .ie n \{\
3678 \h'-04'\(bu\h'+03'\c
3679 .\}
3680 .el \{\
3681 .sp -1
3682 .IP \(bu 2.3
3683 .\}
3684 javac(1)
3685 .RE
3686 .sp
3687 .RS 4
3688 .ie n \{\
3689 \h'-04'\(bu\h'+03'\c
3690 .\}
3691 .el \{\
3692 .sp -1
3693 .IP \(bu 2.3
3694 .\}
3695 jdb(1)
3696 .RE
3697 .sp
3698 .RS 4
3699 .ie n \{\
3700 \h'-04'\(bu\h'+03'\c
3701 .\}
3702 .el \{\
3703 .sp -1
3704 .IP \(bu 2.3
3705 .\}
3706 jar(1)
3707 .RE
3708 .sp
3709 .RS 4
3710 .ie n \{\
3711 \h'-04'\(bu\h'+03'\c
3712 .\}
3713 .el \{\
3714 .sp -1
3715 .IP \(bu 2.3
3716 .\}
3717 jstat(1)
3718 .RE
3719 .br
3720 'pl 8.5i
3721 'bp