Java Options

Java 命令使用介绍

$ info java

Common parameter

理论上来说,虚拟机的堆大小只会受到虚拟内存地址空间大小(比如32位最大是4G)的限制。那么,什么时候操作系统才会真的分配物理内存给虚拟机呢?答案就是,在内存第一次被使用的时候。这个使用并不是说我新建了一个对象,然后操作系统就唰的把所有物理内存分配好了,它只是按照虚拟机的需求,分配了一点点。(实际上是,只是把使用到的这部分内存按照页映射到了物理内存上)

# 操作系统在虚拟机启动的时候就直接完成物理内存的绑定
-XX:+AlwaysPreTouch

Usage And Description

File: *manpages*,  Node: java,  Up: (dir)

java(1)                           Basic Tools                          java(1)



NAME
       java - Launches a Java application.

SYNOPSIS
           java [options] classname [args]

           java [options] -jar filename [args]

       options
           Command-line options separated by spaces. See Options.

       classname
           The name of the class to be launched.

       filename
           The name of the Java Archive (JAR) file to be called. Used only
           with the -jar option.

       args
           The arguments passed to the main() method separated by spaces.

DESCRIPTION
       The java command starts a Java application. It does this by starting
       the Java Runtime Environment (JRE), loading the specified class, and
       calling that class's main() method. The method must be declared public
       and static, it must not return any value, and it must accept a String
       array as a parameter. The method declaration has the following form:

           public static void main(String[] args)


       The java command can be used to launch a JavaFX application by loading
       a class that either has a main() method or that extends
       javafx.application.Application. In the latter case, the launcher
       constructs an instance of the Application class, calls its init()
       method, and then calls the start(javafx.stage.Stage) method.

       By default, the first argument that is not an option of the java
       command is the fully qualified name of the class to be called. If the
       -jar 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 Main-Class manifest header in its source
       code.

       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’s class path.

       Arguments after the class file name or the JAR file name are passed to
       the main() method.

OPTIONS

OPTIONS
       The java command supports a wide range of options that can be divided
       into the following categories:

       ·   Standard Options

       ·   Non-Standard Options

       ·   Advanced Runtime Options

       ·   Advanced JIT Compiler Options

       ·   Advanced Serviceability Options

       ·   Advanced Garbage Collection Options

       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.

       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 -X.

       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
       -XX.

       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.

       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 -XX options are enabled using the
       plus sign (-XX:+OptionName) and disabled using the minus sign
       (-XX:-OptionName).

       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 k or K for kilobytes (KB), m or M
       for megabytes (MB), g or G for gigabytes (GB). For example, to set the
       size to 8 GB, you can specify either 8g, 8192m, 8388608k, or 8589934592
       as the argument. If you are expected to specify the percentage, use a
       number from 0 to 1 (for example, specify 0.25 for 25%).

Standard Options

   Standard Options
       These are the most commonly used options that are supported by all
       implementations of the JVM.

       -agentlib:libname[=options]
           Loads the specified native agent library. After the library name, a
           comma-separated list of options specific to the library can be
           used.

           If the option -agentlib:foo is specified, then the JVM attempts to
           load the library named libfoo.so in the location specified by the
           LD_LIBRARY_PATH system variable (on OS X this variable is
           DYLD_LIBRARY_PATH).

           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:

               -agentlib:hprof=cpu=samples,interval=20,depth=3

           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:

               -agentlib:jdwp=transport=dt_socket,server=y,address=8000

           For more information about the native agent libraries, refer to the
           following:

           ·   The java.lang.instrument package description at
               http://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html

           ·   Agent Command Line Options in the JVM Tools Interface guide at
               http://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#starting

       -agentpath:pathname[=options]
           Loads the native agent library specified by the absolute path name.
           This option is equivalent to -agentlib but uses the full path and
           file name of the library.

       -client
           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.

           For default JVM selection, see Server-Class Machine Detection at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/server-class.html

       -Dproperty=value
           Sets a system property value. The property variable is a string
           with no spaces that represents the name of the property. The value
           variable is a string that represents the value of the property. If
           value is a string with spaces, then enclose it in quotation marks
           (for example -Dfoo="foo bar").

       -d32
           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.

       -d64
           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.

           Currently only the Java HotSpot Server VM supports 64-bit
           operation, and the -server option is implicit with the use of -d64.
           The -client option is ignored with the use of -d64. This is subject
           to change in a future release.

       -disableassertions[:[packagename]...|:classname]
       -da[:[packagename]...|:classname]
           Disables assertions. By default, assertions are disabled in all
           packages and classes.

           With no arguments, -disableassertions (-da) disables assertions in
           all packages and classes. With the packagename argument ending in
           ..., the switch disables assertions in the specified package and
           any subpackages. If the argument is simply ..., then the switch
           disables assertions in the unnamed package in the current working
           directory. With the classname argument, the switch disables
           assertions in the specified class.

           The -disableassertions (-da) 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 -disablesystemassertions option enables you to disable
           assertions in all system classes.

           To explicitly enable assertions in specific packages or classes,
           use the -enableassertions (-ea) option. Both options can be used at
           the same time. For example, to run the MyClass application with
           assertions enabled in package com.wombat.fruitbat (and any
           subpackages) but disabled in class com.wombat.fruitbat.Brickbat,
           use the following command:

               java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat MyClass


       -disablesystemassertions
       -dsa
           Disables assertions in all system classes.

       -enableassertions[:[packagename]...|:classname]
       -ea[:[packagename]...|:classname]
           Enables assertions. By default, assertions are disabled in all
           packages and classes.

           With no arguments, -enableassertions (-ea) enables assertions in
           all packages and classes. With the packagename argument ending in
           ..., the switch enables assertions in the specified package and any
           subpackages. If the argument is simply ..., then the switch enables
           assertions in the unnamed package in the current working directory.
           With the classname argument, the switch enables assertions in the
           specified class.

           The -enableassertions (-ea) 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 -enablesystemassertions option provides a separate switch to
           enable assertions in all system classes.

           To explicitly disable assertions in specific packages or classes,
           use the -disableassertions (-da) 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 MyClass application with assertions enabled only in package
           com.wombat.fruitbat (and any subpackages) but disabled in class
           com.wombat.fruitbat.Brickbat, use the following command:

               java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat MyClass


       -enablesystemassertions
       -esa
           Enables assertions in all system classes.

       -help
       -?
           Displays usage information for the java command without actually
           running the JVM.

       -jar filename
           Executes a program encapsulated in a JAR file. The filename
           argument is the name of a JAR file with a manifest that contains a
           line in the form Main-Class:classname that defines the class with
           the public static void main(String[] args) method that serves as
           your application's starting point.

           When you use the -jar option, the specified JAR file is the source
           of all user classes, and other class path settings are ignored.

           For more information about JAR files, see the following resources:

           ·   jar(1)

           ·   The Java Archive (JAR) Files guide at
               http://docs.oracle.com/javase/8/docs/technotes/guides/jar/index.html

           ·   Lesson: Packaging Programs in JAR Files at

               http://docs.oracle.com/javase/tutorial/deployment/jar/index.html

       -javaagent:jarpath[=options]
           Loads the specified Java programming language agent. For more
           information about instrumenting Java applications, see the
           java.lang.instrument package description in the Java API
           documentation at
           http://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html

       -jre-restrict-search
           Includes user-private JREs in the version search.

       -no-jre-restrict-search
           Excludes user-private JREs from the version search.

       -server
           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.

           For default JVM selection, see Server-Class Machine Detection at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/server-class.html

       -showversion
           Displays version information and continues execution of the
           application. This option is equivalent to the -version option
           except that the latter instructs the JVM to exit after displaying
           version information.

       -splash:imgname
           Shows the splash screen with the image specified by imgname. For
           example, to show the splash.gif file from the images directory when
           starting your application, use the following option:

               -splash:images/splash.gif


       -verbose:class
           Displays information about each loaded class.

       -verbose:gc
           Displays information about each garbage collection (GC) event.

       -verbose:jni
           Displays information about the use of native methods and other Java
           Native Interface (JNI) activity.

       -version
           Displays version information and then exits. This option is
           equivalent to the -showversion option except that the latter does
           not instruct the JVM to exit after displaying version information.

       -version:release
           Specifies the release version to be used for running the
           application. If the version of the java command called does not
           meet this specification and an appropriate implementation is found
           on the system, then the appropriate implementation will be used.

           The release argument specifies either the exact version string, or
           a list of version strings and ranges separated by spaces. A version
           string is the developer designation of the version number in the
           following form: 1.x.0_u (where x is the major version number, and u
           is the update version number). A version range is made up of a
           version string followed by a plus sign (+) to designate this
           version or later, or a part of a version string followed by an
           asterisk (*) to designate any version string with a matching
           prefix. Version strings and ranges can be combined using a space
           for a logical OR combination, or an ampersand (&) for a logical AND
           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:

               -version:"1.6.0_13 1.6* & 1.6.0_10+"

           Quotation marks are necessary only if there are spaces in the
           release parameter.

           For JAR files, the preference is to specify version requirements in
           the JAR file manifest rather than on the command line.

Non-Standard Options

Non-Standard Options
       These options are general purpose options that are specific to the Java
       HotSpot Virtual Machine.

       -X
           Displays help for all available -X options.

       -Xbatch
           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 -Xbatch flag
           disables background compilation so that compilation of all methods
           proceeds as a foreground task until completed.

           This option is equivalent to -XX:-BackgroundCompilation.

       -Xbootclasspath:path
           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.

           Do not deploy applications that use this option to override a class
           in rt.jar, because this violates the JRE binary code license.

       -Xbootclasspath/a:path
           Specifies a list of directories, JAR files, and ZIP archives
           separated by colons (:) to append to the end of the default
           bootstrap class path.

           Do not deploy applications that use this option to override a class
           in rt.jar, because this violates the JRE binary code license.

       -Xbootclasspath/p:path
           Specifies a list of directories, JAR files, and ZIP archives
           separated by colons (:) to prepend to the front of the default
           bootstrap class path.

           Do not deploy applications that use this option to override a class
           in rt.jar, because this violates the JRE binary code license.

       -Xcheck:jni
           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.

       -Xcomp
           Forces compilation of methods on first invocation. By default, the
           Client VM (-client) performs 1,000 interpreted method invocations
           and the Server VM (-server) performs 10,000 interpreted method
           invocations to gather information for efficient compilation.
           Specifying the -Xcomp option disables interpreted method
           invocations to increase compilation performance at the expense of
           efficiency.

           You can also change the number of interpreted method invocations
           before compilation using the -XX:CompileThreshold option.

       -Xdebug
           Does nothing. Provided for backward compatibility.

       -Xdiag
           Shows additional diagnostic messages.

       -Xfuture
           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.

       -Xint
           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.

       -Xinternalversion
           Displays more detailed JVM version information than the -version
           option, and then exits.

       -Xloggc:filename
           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 -verbose:gc with the time elapsed since
           the first GC event preceding each logged event. The -Xloggc option
           overrides -verbose:gc if both are given with the same java command.

           Example:

               -Xloggc:garbage-collection.log


       -Xmaxjitcodesize=size
           Specifies the maximum code cache size (in bytes) for JIT-compiled
           code. Append the letter k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. The default
           maximum code cache size is 240 MB; if you disable tiered
           compilation with the option -XX:-TieredCompilation, then the
           default size is 48 MB:

               -Xmaxjitcodesize=240m

           This option is equivalent to -XX:ReservedCodeCacheSize.

       -Xmixed
           Executes all bytecode by the interpreter except for hot methods,
           which are compiled to native code.

       -Xmnsize
           Sets the initial and maximum size (in bytes) of the heap for the
           young generation (nursery). Append the letter k or K to indicate
           kilobytes, m or M to indicate megabytes, g or G to indicate
           gigabytes.

           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.

           The following examples show how to set the initial and maximum size
           of young generation to 256 MB using various units:

               -Xmn256m
               -Xmn262144k
               -Xmn268435456

           Instead of the -Xmn option to set both the initial and maximum size
           of the heap for the young generation, you can use -XX:NewSize to
           set the initial size and -XX:MaxNewSize to set the maximum size.

       -Xmssize
           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 k or K to
           indicate kilobytes, m or M to indicate megabytes, g or G to
           indicate gigabytes.

           The following examples show how to set the size of allocated memory
           to 6 MB using various units:

               -Xms6291456
               -Xms6144k
               -Xms6m

           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 -Xmn option or the -XX:NewSize option.

       -Xmxsize
           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 k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. The default value
           is chosen at runtime based on system configuration. For server
           deployments, -Xms and -Xmx are often set to the same value. See the
           section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage
           Collection Tuning Guide at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

           The following examples show how to set the maximum allowed size of
           allocated memory to 80 MB using various units:

               -Xmx83886080
               -Xmx81920k
               -Xmx80m

           The -Xmx option is equivalent to -XX:MaxHeapSize.

       -Xnoclassgc
           Disables garbage collection (GC) of classes. This can save some GC
           time, which shortens interruptions during the application run.

           When you specify -Xnoclassgc 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.

       -Xprof
           Profiles the running program and sends profiling data to standard
           output. This option is provided as a utility that is useful in
           program development and is not intended to be used in production
           systems.

       -Xrs
           Reduces the use of operating system signals by the JVM.

           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.

           The JVM catches signals to implement shutdown hooks for unexpected
           termination. The JVM uses SIGHUP, SIGINT, and SIGTERM to initiate
           the running of shutdown hooks.

           The JVM uses a similar mechanism to implement the feature of
           dumping thread stacks for debugging purposes. The JVM uses SIGQUIT
           to perform thread dumps.

           Applications embedding the JVM frequently need to trap signals such
           as SIGINT or SIGTERM, which can lead to interference with the JVM
           signal handlers. The -Xrs option is available to address this
           issue. When -Xrs is used, the signal masks for SIGINT, SIGTERM,
           SIGHUP, and SIGQUIT are not changed by the JVM, and signal handlers
           for these signals are not installed.

           There are two consequences of specifying -Xrs:

           ·   SIGQUIT thread dumps are not available.

           ·   User code is responsible for causing shutdown hooks to run, for
               example, by calling System.exit() when the JVM is to be
               terminated.

       -Xshare:mode
           Sets the class data sharing (CDS) mode. Possible mode arguments for
           this option include the following:

           auto
               Use CDS if possible. This is the default value for Java HotSpot
               32-Bit Client VM.

           on
               Require the use of CDS. Print an error message and exit if
               class data sharing cannot be used.

           off
               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.

           dump
               Manually generate the CDS archive. Specify the application
               class path as described in "Setting the Class Path ".

               You should regenerate the CDS archive with each new JDK
               release.

       -XshowSettings:category
           Shows settings and continues. Possible category arguments for this
           option include the following:

           all
               Shows all categories of settings. This is the default value.

           locale
               Shows settings related to locale.

           properties
               Shows settings related to system properties.

           vm
               Shows the settings of the JVM.

       -Xsssize
           Sets the thread stack size (in bytes). Append the letter k or K to
           indicate KB, m or M to indicate MB, g or G to indicate GB. The
           default value depends on the platform:

           ·   Linux/ARM (32-bit): 320 KB

           ·   Linux/i386 (32-bit): 320 KB

           ·   Linux/x64 (64-bit): 1024 KB

           ·   OS X (64-bit): 1024 KB

           ·   Oracle Solaris/i386 (32-bit): 320 KB

           ·   Oracle Solaris/x64 (64-bit): 1024 KB

           The following examples set the thread stack size to 1024 KB in
           different units:

               -Xss1m
               -Xss1024k
               -Xss1048576

           This option is equivalent to -XX:ThreadStackSize.

       -Xusealtsigs
           Use alternative signals instead of SIGUSR1 and SIGUSR2 for JVM
           internal signals. This option is equivalent to -XX:+UseAltSigs.


       -Xverify:mode
           Sets the mode of the bytecode verifier. Bytecode verification
           ensures that class files are properly formed and satisfy the
           constraints listed in section 4.10, "Verification of class Files"
           in the The Java Virtual Machine Specification:

           https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.10

           Do not turn off verification as this reduces the protection
           provided by Java and could cause problems due to ill-formed class
           files.

           Possible mode arguments for this option include the following:

           remote
               Verifies all bytecodes not loaded by the bootstrap class
               loader. This is the default behavior if you do not specify the
               -Xverify option.

           all
               Enables verification of all bytecodes.

           none
               Disables verification of all bytecodes. Use of -Xverify:none is
               unsupported.

Advanced Runtime Options

   Advanced Runtime Options
       These options control the runtime behavior of the Java HotSpot VM.

       -XX:+CheckEndorsedAndExtDirs
           Enables the option to prevent the java command from running a Java
           application if it uses the endorsed-standards override mechanism or
           the extension mechanism. This option checks if an application is
           using one of these mechanisms by checking the following:

           ·   The java.ext.dirs or java.endorsed.dirs system property is set.

           ·   The lib/endorsed directory exists and is not empty.

           ·   The lib/ext directory contains any JAR files other than those
               of the JDK.

           ·   The system-wide platform-specific extension directory contains
               any JAR files.

       -XX:+DisableAttachMechanism
           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
           jcmd, jstack, jmap, and jinfo.

       -XX:ErrorFile=filename
           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
           hs_err_pidpid.log where pid 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 %p):

               -XX:ErrorFile=./hs_err_pid%p.log

           The following example shows how to set the error log to
           /var/log/java/java_error.log:

               -XX:ErrorFile=/var/log/java/java_error.log

           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 /tmp.

       -XX:+FailOverToOldVerifier
           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.

       -XX:+FlightRecorder
           Enables the use of the Java Flight Recorder (JFR) during the
           runtime of the application. This is a commercial feature that works
           in conjunction with the -XX:+UnlockCommercialFeatures option as
           follows:

               java -XX:+UnlockCommercialFeatures -XX:+FlightRecorder

           If this option is not provided, Java Flight Recorder can still be
           enabled in a running JVM by providing the appropriate jcmd
           diagnostic commands.

       -XX:-FlightRecorder
           Disables the use of the Java Flight Recorder (JFR) during the
           runtime of the application. This is a commercial feature that works
           in conjunction with the -XX:+UnlockCommercialFeatures option as
           follows:

               java -XX:+UnlockCommercialFeatures -XX:-FlightRecorder

           If this option is provided, Java Flight Recorder cannot be enabled
           in a running JVM.

       -XX:FlightRecorderOptions=parameter=value
           Sets the parameters that control the behavior of JFR. This is a
           commercial feature that works in conjunction with the
           -XX:+UnlockCommercialFeatures option. This option can be used only
           when JFR is enabled (that is, the -XX:+FlightRecorder option is
           specified).

           The following list contains all available JFR parameters:

           defaultrecording={true|false}
               Specifies whether the recording is a continuous background
               recording or if it runs for a limited time. By default, this
               parameter is set to false (recording runs for a limited time).
               To make the recording run continuously, set the parameter to
               true.

           disk={true|false}
               Specifies whether JFR should write a continuous recording to
               disk. By default, this parameter is set to false (continuous
               recording to disk is disabled). To enable it, set the parameter
               to true, and also set defaultrecording=true.

           dumponexit={true|false}
               Specifies whether a dump file of JFR data should be generated
               when the JVM terminates in a controlled manner. By default,
               this parameter is set to false (dump file on exit is not
               generated). To enable it, set the parameter to true, and also
               set defaultrecording=true.

               The dump file is written to the location defined by the
               dumponexitpath parameter.

           dumponexitpath=path
               Specifies the path and name of the dump file with JFR data that
               is created when the JVM exits in a controlled manner if you set
               the dumponexit=true parameter. Setting the path makes sense
               only if you also set defaultrecording=true.

               If the specified path is a directory, the JVM assigns a file
               name that shows the creation date and time. If the specified
               path includes a file name and if that file already exists, the
               JVM creates a new file by appending the date and time stamp to
               the specified file name.

           globalbuffersize=size
               Specifies the total amount of primary memory (in bytes) used
               for data retention. Append k or K, to specify the size in KB, m
               or M to specify the size in MB, g or G to specify the size in
               GB. By default, the size is set to 462848 bytes.

           loglevel={quiet|error|warning|info|debug|trace}
               Specify the amount of data written to the log file by JFR. By
               default, it is set to info.

           maxage=time
               Specifies the maximum age of disk data to keep for the default
               recording. Append s to specify the time in seconds, m for
               minutes, h for hours, or d for days (for example, specifying
               30s means 30 seconds). By default, the maximum age is set to 15
               minutes (15m).

               This parameter is valid only if you set the disk=true
               parameter.

           maxchunksize=size
               Specifies the maximum size (in bytes) of the data chunks in a
               recording. Append k or K, to specify the size in KB, m or M to
               specify the size in MB, g or G to specify the size in GB. By
               default, the maximum size of data chunks is set to 12 MB.

           maxsize=size
               Specifies the maximum size (in bytes) of disk data to keep for
               the default recording. Append k or K, to specify the size in
               KB, m or M to specify the size in MB, g or G to specify the
               size in GB. By default, the maximum size of disk data is not
               limited, and this parameter is set to 0.

               This parameter is valid only if you set the disk=true
               parameter.

           repository=path
               Specifies the repository (a directory) for temporary disk
               storage. By default, the system’s temporary directory is used.

           samplethreads={true|false}
               Specifies whether thread sampling is enabled. Thread sampling
               occurs only if the sampling event is enabled along with this
               parameter. By default, this parameter is enabled.

           settings=path
               Specifies the path and name of the event settings file (of type
               JFC). By default, the default.jfc file is used, which is
               located in JAVA_HOME/jre/lib/jfr.

           stackdepth=depth
               Stack depth for stack traces by JFR. By default, the depth is
               set to 64 method calls. The maximum is 2048, minimum is 1.

           threadbuffersize=size
               Specifies the per-thread local buffer size (in bytes). Append k
               or K, to specify the size in KB, m or M to specify the size in
               MB, g or G to specify the size in GB. Higher values for this
               parameter allow more data gathering without contention to flush
               it to the global storage. It can increase application footprint
               in a thread-rich environment. By default, the local buffer size
               is set to 5 KB.

           You can specify values for multiple parameters by separating them
           with a comma. For example, to instruct JFR to write a continuous
           recording to disk, and set the maximum size of data chunks to 10
           MB, specify the following:

               -XX:FlightRecorderOptions=defaultrecording=true,disk=true,maxchunksize=10M


       -XX:LargePageSizeInBytes=size
           On Solaris, sets the maximum size (in bytes) for large pages used
           for Java heap. The size argument must be a power of 2 (2, 4, 8, 16,
           ...). Append the letter k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. By default, the
           size is set to 0, meaning that the JVM chooses the size for large
           pages automatically.

           The following example illustrates how to set the large page size to
           4 megabytes (MB):

               -XX:LargePageSizeInBytes=4m


       -XX:MaxDirectMemorySize=size
           Sets the maximum total size (in bytes) of the New I/O (the java.nio
           package) direct-buffer allocations. Append the letter k or K to
           indicate kilobytes, m or M to indicate megabytes, g or G to
           indicate gigabytes. By default, the size is set to 0, meaning that
           the JVM chooses the size for NIO direct-buffer allocations
           automatically.

           The following examples illustrate how to set the NIO size to 1024
           KB in different units:

               -XX:MaxDirectMemorySize=1m
               -XX:MaxDirectMemorySize=1024k
               -XX:MaxDirectMemorySize=1048576


       -XX:NativeMemoryTracking=mode
           Specifies the mode for tracking JVM native memory usage. Possible
           mode arguments for this option include the following:

           off
               Do not track JVM native memory usage. This is the default
               behavior if you do not specify the -XX:NativeMemoryTracking
               option.

           summary
               Only track memory usage by JVM subsystems, such as Java heap,
               class, code, and thread.

           detail
               In addition to tracking memory usage by JVM subsystems, track
               memory usage by individual CallSite, individual virtual memory
               region and its committed regions.

       -XX:ObjectAlignmentInBytes=alignment
           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.

           The heap size limit in bytes is calculated as:

           4GB * ObjectAlignmentInBytes

           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.

       -XX:OnError=string
           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.

           The following example shows how the -XX:OnError option can be used
           to run the gcore command to create the core image, and the debugger
           is started to attach to the process in case of an irrecoverable
           error (the %p designates the current process):

               -XX:OnError="gcore %p;dbx - %p"


       -XX:OnOutOfMemoryError=string
           Sets a custom command or a series of semicolon-separated commands
           to run when an OutOfMemoryError 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 -XX:OnError option.

       -XX:+PerfDataSaveToFile
           If enabled, saves jstat(1) binary data when the Java application
           exits. This binary data is saved in a file named hsperfdata_<pid>,
           where <pid> is the process identifier of the Java application you
           ran. Use jstat to display the performance data contained in this
           file as follows:

               jstat -class file:///<path>/hsperfdata_<pid>
               jstat -gc file:///<path>/hsperfdata_<pid>

       -XX:+PrintCommandLineFlags
           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.

       -XX:+PrintNMTStatistics
           Enables printing of collected native memory tracking data at JVM
           exit when native memory tracking is enabled (see
           -XX:NativeMemoryTracking). By default, this option is disabled and
           native memory tracking data is not printed.

       -XX:+RelaxAccessControlCheck
           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.

       -XX:+ResourceManagement
           Enables the use of Resource Management during the runtime of the
           application.

           This is a commercial feature that requires you to also specify the
           -XX:+UnlockCommercialFeatures option as follows:

           java -XX:+UnlockCommercialFeatures -XX:+ResourceManagement

       -XX:ResourceManagementSampleInterval=value (milliseconds)
           Sets the parameter that controls the sampling interval for Resource
           Management measurements, in milliseconds.

           This option can be used only when Resource Management is enabled
           (that is, the -XX:+ResourceManagement option is specified).

       -XX:SharedArchiveFile=path
           Specifies the path and name of the class data sharing (CDS) archive
           file

       -XX:SharedClassListFile=file_name
           Specifies the text file that contains the names of the class files
           to store in the class data sharing (CDS) archive. This file
           contains the full name of one class file per line, except slashes
           (/) replace dots (.). For example, to specify the classes
           java.lang.Object and hello.Main, create a text file that contains
           the following two lines:

               java/lang/Object
               hello/Main

           The class files that you specify in this text file should include
           the classes that are commonly used by the application. They may
           include any classes from the application, extension, or bootstrap
           class paths.

       -XX:+ShowMessageBoxOnError
           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.

       -XX:StartFlightRecording=parameter=value
           Starts a JFR recording for the Java application. This is a
           commercial feature that works in conjunction with the
           -XX:+UnlockCommercialFeatures option. This option is equivalent to
           the JFR.start diagnostic command that starts a recording during
           runtime. You can set the following parameters when starting a JFR
           recording:

           compress={true|false}
               Specifies whether to compress the JFR recording log file (of
               type JFR) on the disk using the gzip file compression utility.
               This parameter is valid only if the filename parameter is
               specified. By default it is set to false (recording is not
               compressed). To enable compression, set the parameter to true.

           defaultrecording={true|false}
               Specifies whether the recording is a continuous background
               recording or if it runs for a limited time. By default, this
               parameter is set to false (recording runs for a limited time).
               To make the recording run continuously, set the parameter to
               true.

           delay=time
               Specifies the delay between the Java application launch time
               and the start of the recording. Append s to specify the time in
               seconds, m for minutes, h for hours, or d for days (for
               example, specifying 10m means 10 minutes). By default, there is
               no delay, and this parameter is set to 0.

           dumponexit={true|false}
               Specifies whether a dump file of JFR data should be generated
               when the JVM terminates in a controlled manner. By default,
               this parameter is set to false (dump file on exit is not
               generated). To enable it, set the parameter to true.

               The dump file is written to the location defined by the
               filename parameter.

               Example:

                   -XX:StartFlightRecording=name=test,filename=D:\test.jfr,dumponexit=true

           duration=time
               Specifies the duration of the recording. Append s to specify
               the time in seconds, m for minutes, h for hours, or d for days
               (for example, specifying 5h means 5 hours). By default, the
               duration is not limited, and this parameter is set to 0.

           filename=path
               Specifies the path and name of the JFR recording log file.

           name=identifier
               Specifies the identifier for the JFR recording. By default, it
               is set to Recording x.

           maxage=time
               Specifies the maximum age of disk data to keep for the default
               recording. Append s to specify the time in seconds, m for
               minutes, h for hours, or d for days (for example, specifying
               30s means 30 seconds). By default, the maximum age is set to 15
               minutes (15m).

           maxsize=size
               Specifies the maximum size (in bytes) of disk data to keep for
               the default recording. Append k or K, to specify the size in
               KB, m or M to specify the size in MB, g or G to specify the
               size in GB. By default, the maximum size of disk data is not
               limited, and this parameter is set to 0.

           settings=path
               Specifies the path and name of the event settings file (of type
               JFC). By default, the default.jfc file is used, which is
               located in JAVA_HOME/jre/lib/jfr.

           You can specify values for multiple parameters by separating them
           with a comma. For example, to save the recording to test.jfr in the
           current working directory, and instruct JFR to compress the log
           file, specify the following:

               -XX:StartFlightRecording=filename=test.jfr,compress=true


       -XX:ThreadStackSize=size
           Sets the thread stack size (in bytes). Append the letter k or K to
           indicate kilobytes, m or M to indicate megabytes, g or G to
           indicate gigabytes. The default value depends on the platform:

           ·   Linux/ARM (32-bit): 320 KB

           ·   Linux/i386 (32-bit): 320 KB

           ·   Linux/x64 (64-bit): 1024 KB

           ·   OS X (64-bit): 1024 KB

           ·   Oracle Solaris/i386 (32-bit): 320 KB

           ·   Oracle Solaris/x64 (64-bit): 1024 KB

           The following examples show how to set the thread stack size to
           1024 KB in different units:

               -XX:ThreadStackSize=1m
               -XX:ThreadStackSize=1024k
               -XX:ThreadStackSize=1048576

           This option is equivalent to -Xss.

       -XX:+TraceClassLoading
           Enables tracing of classes as they are loaded. By default, this
           option is disabled and classes are not traced.

       -XX:+TraceClassLoadingPreorder
           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.

       -XX:+TraceClassResolution
           Enables tracing of constant pool resolutions. By default, this
           option is disabled and constant pool resolutions are not traced.

       -XX:+TraceClassUnloading
           Enables tracing of classes as they are unloaded. By default, this
           option is disabled and classes are not traced.

       -XX:+TraceLoaderConstraints
           Enables tracing of the loader constraints recording. By default,
           this option is disabled and loader constraints recording is not
           traced.

       -XX:+UnlockCommercialFeatures
           Enables the use of commercial features. Commercial features are
           included with Oracle Java SE Advanced or Oracle Java SE Suite
           packages, as defined on the Java SE Products page at
           http://www.oracle.com/technetwork/java/javase/terms/products/index.html

           By default, this option is disabled and the JVM runs without the
           commercial features. Once they were enabled for a JVM process, it
           is not possible to disable their use for that process.

           If this option is not provided, commercial features can still be
           unlocked in a running JVM by using the appropriate jcmd diagnostic
           commands.

       -XX:+UseAltSigs
           Enables the use of alternative signals instead of SIGUSR1 and
           SIGUSR2 for JVM internal signals. By default, this option is
           disabled and alternative signals are not used. This option is
           equivalent to -Xusealtsigs.

       -XX:+UseAppCDS
           Enables application class data sharing (AppCDS). To use AppCDS, you
           must also specify values for the options -XX:SharedClassListFile
           and -XX:SharedArchiveFile during both CDS dump time (see the option
           -Xshare:dump) and application run time.

           This is a commercial feature that requires you to also specify the
           -XX:+UnlockCommercialFeatures option. This is also an experimental
           feature; it may change in future releases.

           See "Application Class Data Sharing".

       -XX:-UseBiasedLocking
           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

           By default, this option is enabled.

       -XX:-UseCompressedOops
           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.

           It is also possible to use compressed pointers when Java heap sizes
           are greater than 32GB. See the -XX:ObjectAlignmentInBytes option.

       -XX:+UseHugeTLBFS
           This option for Linux is the equivalent of specifying
           -XX:+UseLargePages. 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 -XX:UseTransparentHugePages if you want this
           behavior.

           For more information, see "Large Pages".

       -XX:+UseLargePages
           Enables the use of large page memory. By default, this option is
           disabled and large page memory is not used.

           For more information, see "Large Pages".

       -XX:+UseMembar
           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.)

       -XX:+UsePerfData
           Enables the perfdata feature. This option is enabled by default to
           allow JVM monitoring and performance testing. Disabling it
           suppresses the creation of the hsperfdata_userid directories. To
           disable the perfdata feature, specify -XX:-UsePerfData.

       -XX:+UseTransparentHugePages
           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.

           For more information, see "Large Pages".

       -XX:+AllowUserSignalHandlers
           Enables installation of signal handlers by the application. By
           default, this option is disabled and the application is not allowed
           to install signal handlers.

Advanced JIT Compiler Options

   Advanced JIT Compiler Options
       These options control the dynamic just-in-time (JIT) compilation
       performed by the Java HotSpot VM.

       -XX:+AggressiveOpts
           Enables the use of aggressive performance optimization features,
           which are expected to become default in upcoming releases. By
           default, this option is disabled and experimental performance
           features are not used.

       -XX:AllocateInstancePrefetchLines=lines
           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:

               -XX:AllocateInstancePrefetchLines=1

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchDistance=size
           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.

           Negative values denote that prefetch distance is chosen based on
           the platform. Positive values are bytes to prefetch. Append the
           letter k or K to indicate kilobytes, m or M to indicate megabytes,
           g or G to indicate gigabytes. The default value is set to -1.

           The following example shows how to set the prefetch distance to
           1024 bytes:

               -XX:AllocatePrefetchDistance=1024

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchInstr=instruction
           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:

               -XX:AllocatePrefetchInstr=0

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchLines=lines
           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.

           The following example shows how to set the number of loaded cache
           lines to 5:

               -XX:AllocatePrefetchLines=5

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchStepSize=size
           Sets the step size (in bytes) for sequential prefetch instructions.
           Append the letter k or K to indicate kilobytes, m or M to indicate
           megabytes, g or G to indicate gigabytes. By default, the step size
           is set to 16 bytes:

               -XX:AllocatePrefetchStepSize=16

           Only the Java HotSpot Server VM supports this option.

       -XX:AllocatePrefetchStyle=style
           Sets the generated code style for prefetch instructions. The style
           argument is an integer from 0 to 3:

           0
               Do not generate prefetch instructions.

           1
               Execute prefetch instructions after each allocation. This is
               the default parameter.

           2
               Use the thread-local allocation block (TLAB) watermark pointer
               to determine when prefetch instructions are executed.

           3
               Use BIS instruction on SPARC for allocation prefetch.

           Only the Java HotSpot Server VM supports this option.

       -XX:+BackgroundCompilation
           Enables background compilation. This option is enabled by default.
           To disable background compilation, specify
           -XX:-BackgroundCompilation (this is equivalent to specifying
           -Xbatch).

       -XX:CICompilerCount=threads
           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:

               -XX:CICompilerCount=2


       -XX:CodeCacheMinimumFreeSpace=size
           Sets the minimum free space (in bytes) required for compilation.
           Append the letter k or K to indicate kilobytes, m or M to indicate
           megabytes, g or G 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:

               -XX:CodeCacheMinimumFreeSpace=1024m


       -XX:CompileCommand=command,method[,option]
           Specifies a command to perform on a method. For example, to exclude
           the indexOf() method of the String class from being compiled, use
           the following:

               -XX:CompileCommand=exclude,java/lang/String.indexOf

           Note that the full class name is specified, including all packages
           and subpackages separated by a slash (/). For easier cut and paste
           operations, it is also possible to use the method name format
           produced by the -XX:+PrintCompilation and -XX:+LogCompilation
           options:

               -XX:CompileCommand=exclude,java.lang.String::indexOf

           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 indexOf(String) method
           of the String class from being compiled, use the following:

               -XX:CompileCommand="exclude,java/lang/String.indexOf,(Ljava/lang/String;)I"

           You can also use the asterisk (*) as a wildcard for class and
           method names. For example, to exclude all indexOf() methods in all
           classes from being compiled, use the following:

               -XX:CompileCommand=exclude,*.indexOf

           The commas and periods are aliases for spaces, making it easier to
           pass compiler commands through a shell. You can pass arguments to
           -XX:CompileCommand using spaces as separators by enclosing the
           argument in quotation marks:

               -XX:CompileCommand="exclude java/lang/String indexOf"

           Note that after parsing the commands passed on the command line
           using the -XX:CompileCommand options, the JIT compiler then reads
           commands from the .hotspot_compiler file. You can add commands to
           this file or specify a different file using the
           -XX:CompileCommandFile option.

           To add several commands, either specify the -XX:CompileCommand
           option multiple times, or separate each argument with the newline
           separator (\n). The following commands are available:

           break
               Set a breakpoint when debugging the JVM to stop at the
               beginning of compilation of the specified method.

           compileonly
               Exclude all methods from compilation except for the specified
               method. As an alternative, you can use the -XX:CompileOnly
               option, which allows to specify several methods.

           dontinline
               Prevent inlining of the specified method.

           exclude
               Exclude the specified method from compilation.

           help
               Print a help message for the -XX:CompileCommand option.

           inline
               Attempt to inline the specified method.

           log
               Exclude compilation logging (with the -XX:+LogCompilation
               option) for all methods except for the specified method. By
               default, logging is performed for all compiled methods.

           option
               This command can be used to pass a JIT compilation option to
               the specified method in place of the last argument (option).
               The compilation option is set at the end, after the method
               name. For example, to enable the BlockLayoutByFrequency option
               for the append() method of the StringBuffer class, use the
               following:

                   -XX:CompileCommand=option,java/lang/StringBuffer.append,BlockLayoutByFrequency

               You can specify multiple compilation options, separated by
               commas or spaces.

           print
               Print generated assembler code after compilation of the
               specified method.

           quiet
               Do not print the compile commands. By default, the commands
               that you specify with the -XX:CompileCommand option are
               printed; for example, if you exclude from compilation the
               indexOf() method of the String class, then the following will
               be printed to standard output:

                   CompilerOracle: exclude java/lang/String.indexOf

               You can suppress this by specifying the
               -XX:CompileCommand=quiet option before other -XX:CompileCommand
               options.

       -XX:CompileCommandFile=filename
           Sets the file from which JIT compiler commands are read. By
           default, the .hotspot_compiler file is used to store commands
           performed by the JIT compiler.

           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 toString() method of the String
           class:

               print java/lang/String toString

           For more information about specifying the commands for the JIT
           compiler to perform on methods, see the -XX:CompileCommand option.

       -XX:CompileOnly=methods
           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
           length() method of the String class and the size() method of the
           List class, use the following:

               -XX:CompileOnly=java/lang/String.length,java/util/List.size

           Note that the full class name is specified, including all packages
           and subpackages separated by a slash (/). For easier cut and paste
           operations, it is also possible to use the method name format
           produced by the -XX:+PrintCompilation and -XX:+LogCompilation
           options:

               -XX:CompileOnly=java.lang.String::length,java.util.List::size

           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:

               -XX:CompileOnly=java/lang/String
               -XX:CompileOnly=java/lang
               -XX:CompileOnly=.length


       -XX:CompileThreshold=invocations
           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
           -XX:+TieredCompilation. The following example shows how to set the
           number of interpreted method invocations to 5,000:

               -XX:CompileThreshold=5000

           You can completely disable interpretation of Java methods before
           compilation by specifying the -Xcomp option.

       -XX:+DoEscapeAnalysis
           Enables the use of escape analysis. This option is enabled by
           default. To disable the use of escape analysis, specify
           -XX:-DoEscapeAnalysis. Only the Java HotSpot Server VM supports
           this option.

       -XX:InitialCodeCacheSize=size
           Sets the initial code cache size (in bytes). Append the letter k or
           K to indicate kilobytes, m or M to indicate megabytes, g or G to
           indicate gigabytes. The default value is set to 500 KB. The initial
           code cache size should be not less than the system's minimal memory
           page size. The following example shows how to set the initial code
           cache size to 32 KB:

               -XX:InitialCodeCacheSize=32k


       -XX:+Inline
           Enables method inlining. This option is enabled by default to
           increase performance. To disable method inlining, specify
           -XX:-Inline.

       -XX:InlineSmallCode=size
           Sets the maximum code size (in bytes) for compiled methods that
           should be inlined. Append the letter k or K to indicate kilobytes,
           m or M to indicate megabytes, g or G 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:

               -XX:InlineSmallCode=1000


       -XX:+LogCompilation
           Enables logging of compilation activity to a file named hotspot.log
           in the current working directory. You can specify a different log
           file path and name using the -XX:LogFile option.

           By default, this option is disabled and compilation activity is not
           logged. The -XX:+LogCompilation option has to be used together with
           the -XX:UnlockDiagnosticVMOptions option that unlocks diagnostic
           JVM options.

           You can enable verbose diagnostic output with a message printed to
           the console every time a method is compiled by using the
           -XX:+PrintCompilation option.

       -XX:MaxInlineSize=size
           Sets the maximum bytecode size (in bytes) of a method to be
           inlined. Append the letter k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. By default, the
           maximum bytecode size is set to 35 bytes:

               -XX:MaxInlineSize=35


       -XX:MaxNodeLimit=nodes
           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:

               -XX:MaxNodeLimit=65000


       -XX:MaxTrivialSize=size
           Sets the maximum bytecode size (in bytes) of a trivial method to be
           inlined. Append the letter k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. By default, the
           maximum bytecode size of a trivial method is set to 6 bytes:

               -XX:MaxTrivialSize=6


       -XX:+OptimizeStringConcat
           Enables the optimization of String concatenation operations. This
           option is enabled by default. To disable the optimization of String
           concatenation operations, specify -XX:-OptimizeStringConcat. Only
           the Java HotSpot Server VM supports this option.

       -XX:+PrintAssembly
           Enables printing of assembly code for bytecoded and native methods
           by using the external disassembler.so library. This enables you to
           see the generated code, which may help you to diagnose performance
           issues.

           By default, this option is disabled and assembly code is not
           printed. The -XX:+PrintAssembly option has to be used together with
           the -XX:UnlockDiagnosticVMOptions option that unlocks diagnostic
           JVM options.

       -XX:+PrintCompilation
           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.

           You can also log compilation activity to a file by using the
           -XX:+LogCompilation option.

       -XX:+PrintInlining
           Enables printing of inlining decisions. This enables you to see
           which methods are getting inlined.

           By default, this option is disabled and inlining information is not
           printed. The -XX:+PrintInlining option has to be used together with
           the -XX:+UnlockDiagnosticVMOptions option that unlocks diagnostic
           JVM options.

       -XX:ReservedCodeCacheSize=size
           Sets the maximum code cache size (in bytes) for JIT-compiled code.
           Append the letter k or K to indicate kilobytes, m or M to indicate
           megabytes, g or G to indicate gigabytes. The default maximum code
           cache size is 240 MB; if you disable tiered compilation with the
           option -XX:-TieredCompilation, 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 -XX:InitialCodeCacheSize. This option is
           equivalent to -Xmaxjitcodesize.

       -XX:RTMAbortRatio=abort_ratio
           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 -XX:+UseRTMDeopt 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.

       -XX:RTMRetryCount=number_of_retries
           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 -XX:UseRTMLocking option must be enabled.

       -XX:-TieredCompilation
           Disables the use of tiered compilation. By default, this option is
           enabled. Only the Java HotSpot Server VM supports this option.

       -XX:+UseAES
           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.

       -XX:+UseAESIntrinsics
           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 -XX:-UseAES
           -XX:-UseAESIntrinsics. For example, to enable hardware AES, use the
           following flags:

               -XX:+UseAES -XX:+UseAESIntrinsics

           To support UseAES and UseAESIntrinsics flags for 32-bit and 64-bit
           use -server option to choose Java HotSpot Server VM. These flags
           are not supported on Client VM.

       -XX:+UseCodeCacheFlushing
           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
           -XX:-UseCodeCacheFlushing.

       -XX:+UseCondCardMark
           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.

       -XX:+UseRTMDeopt
           Auto-tunes RTM locking depending on the abort ratio. This ratio is
           specified by -XX:RTMAbortRatio 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
           -XX:+UseRTMLocking option must be enabled.

       -XX:+UseRTMLocking
           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).

           RTM is part of Intel's TSX, which is an x86 instruction set
           extension and facilitates the creation of multithreaded
           applications. RTM introduces the new instructions XBEGIN, XABORT,
           XEND, and XTEST. The XBEGIN and XEND 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 XEND instruction. The XABORT instruction
           can be used to explicitly abort a transaction and the XEND
           instruction to check if a set of instructions are being run in a
           transaction.

           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's system.

           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.

       -XX:+UseSHA
           Enables hardware-based intrinsics for SHA crypto hash functions for
           SPARC hardware.  UseSHA is used in conjunction with the
           UseSHA1Intrinsics, UseSHA256Intrinsics, and UseSHA512Intrinsics
           options.

           The UseSHA and UseSHA*Intrinsics flags are enabled by default, and
           are supported only for Java HotSpot Server VM 64-bit on SPARC T4
           and newer.

           This feature is only applicable when using the
           sun.security.provider.Sun provider for SHA operations.

           To disable all hardware-based SHA intrinsics, specify -XX:-UseSHA.
           To disable only a particular SHA intrinsic, use the appropriate
           corresponding option. For example: -XX:-UseSHA256Intrinsics.

       -XX:+UseSHA1Intrinsics
           Enables intrinsics for SHA-1 crypto hash function.

       -XX:+UseSHA256Intrinsics
           Enables intrinsics for SHA-224 and SHA-256 crypto hash functions.

       -XX:+UseSHA512Intrinsics
           Enables intrinsics for SHA-384 and SHA-512 crypto hash functions.

       -XX:+UseSuperWord
           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 -XX:-UseSuperWord. Only the Java HotSpot Server VM supports
           this option.

Advanced Serviceability Options

   Advanced Serviceability Options
       These options provide the ability to gather system information and
       perform extensive debugging.

       -XX:+ExtendedDTraceProbes
           Enables additional dtrace tool probes that impact the performance.
           By default, this option is disabled and dtrace performs only
           standard probes.

       -XX:+HeapDumpOnOutOfMemory
           Enables the dumping of the Java heap to a file in the current
           directory by using the heap profiler (HPROF) when a
           java.lang.OutOfMemoryError exception is thrown. You can explicitly
           set the heap dump file path and name using the -XX:HeapDumpPath
           option. By default, this option is disabled and the heap is not
           dumped when an OutOfMemoryError exception is thrown.

       -XX:HeapDumpPath=path
           Sets the path and file name for writing the heap dump provided by
           the heap profiler (HPROF) when the -XX:+HeapDumpOnOutOfMemoryError
           option is set. By default, the file is created in the current
           working directory, and it is named java_pidpid.hprof where pid is
           the identifier of the process that caused the error. The following
           example shows how to set the default file explicitly (%p represents
           the current process identificator):

               -XX:HeapDumpPath=./java_pid%p.hprof

           The following example shows how to set the heap dump file to
           /var/log/java/java_heapdump.hprof:

               -XX:HeapDumpPath=/var/log/java/java_heapdump.hprof


       -XX:LogFile=path
           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 hotspot.log.

           The following example shows how to set the log file to
           /var/log/java/hotspot.log:

               -XX:LogFile=/var/log/java/hotspot.log


       -XX:+PrintClassHistogram
           Enables printing of a class instance histogram after a Control+C
           event (SIGTERM). By default, this option is disabled.

           Setting this option is equivalent to running the jmap -histo
           command, or the jcmd pid GC.class_histogram command, where pid is
           the current Java process identifier.

       -XX:+PrintConcurrentLocks
           Enables printing of locks after a event. By default, this option is
           disabled.

           Enables printing of java.util.concurrent locks after a Control+C
           event (SIGTERM). By default, this option is disabled.

           Setting this option is equivalent to running the jstack -l command
           or the jcmd pid Thread.print -l command, where pid is the current
           Java process identifier.

       -XX:+UnlockDiagnosticVMOptions
           Unlocks the options intended for diagnosing the JVM. By default,
           this option is disabled and diagnostic options are not available.

Advanced Garbage Collection Options

   Advanced Garbage Collection Options
       These options control how garbage collection (GC) is performed by the
       Java HotSpot VM.

       -XX:+AggressiveHeap
           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.

       -XX:+AlwaysPreTouch
           Enables touching of every page on the Java heap during JVM
           initialization. This gets all pages into the memory before entering
           the main() 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.

       -XX:+CMSClassUnloadingEnabled
           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
           -XX:-CMSClassUnloadingEnabled.

       -XX:CMSExpAvgFactor=percent
           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%:

               -XX:CMSExpAvgFactor=15


       -XX:CMSInitiatingOccupancyFraction=percent
           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
           -XX:CMSTriggerRatio is used to define the value of the initiating
           occupancy fraction.

           The following example shows how to set the occupancy fraction to
           20%:

               -XX:CMSInitiatingOccupancyFraction=20


       -XX:+CMSScavengeBeforeRemark
           Enables scavenging attempts before the CMS remark step. By default,
           this option is disabled.

       -XX:CMSTriggerRatio=percent
           Sets the percentage (0 to 100) of the value specified by
           -XX:MinHeapFreeRatio that is allocated before a CMS collection
           cycle commences. The default value is set to 80%.

           The following example shows how to set the occupancy fraction to
           75%:

               -XX:CMSTriggerRatio=75


       -XX:ConcGCThreads=threads
           Sets the number of threads used for concurrent GC. The default
           value depends on the number of CPUs available to the JVM.

           For example, to set the number of threads for concurrent GC to 2,
           specify the following option:

               -XX:ConcGCThreads=2


       -XX:+DisableExplicitGC
           Enables the option that disables processing of calls to
           System.gc(). This option is disabled by default, meaning that calls
           to System.gc() are processed. If processing of calls to System.gc()
           is disabled, the JVM still performs GC when necessary.

       -XX:+ExplicitGCInvokesConcurrent
           Enables invoking of concurrent GC by using the System.gc() request.
           This option is disabled by default and can be enabled only together
           with the -XX:+UseConcMarkSweepGC option.

       -XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses
           Enables invoking of concurrent GC by using the System.gc() request
           and unloading of classes during the concurrent GC cycle. This
           option is disabled by default and can be enabled only together with
           the -XX:+UseConcMarkSweepGC option.

       -XX:G1HeapRegionSize=size
           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.

           The following example shows how to set the size of the subdivisions
           to 16 MB:

               -XX:G1HeapRegionSize=16m


       -XX:+G1PrintHeapRegions
           Enables the printing of information about which regions are
           allocated and which are reclaimed by the G1 collector. By default,
           this option is disabled.

       -XX:G1ReservePercent=percent
           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%.

           The following example shows how to set the reserved heap to 20%:

               -XX:G1ReservePercent=20


       -XX:InitialHeapSize=size
           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 k or K to indicate kilobytes, m or M to
           indicate megabytes, g or G to indicate gigabytes. The default value
           is chosen at runtime based on system configuration. See the section
           "Ergonomics" in Java SE HotSpot Virtual Machine Garbage Collection
           Tuning Guide at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

           The following examples show how to set the size of allocated memory
           to 6 MB using various units:

               -XX:InitialHeapSize=6291456
               -XX:InitialHeapSize=6144k
               -XX:InitialHeapSize=6m

           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 -XX:NewSize option.

       -XX:InitialSurvivorRatio=ratio
           Sets the initial survivor space ratio used by the throughput
           garbage collector (which is enabled by the -XX:+UseParallelGC
           and/or -XX:+UseParallelOldGC options). Adaptive sizing is enabled
           by default with the throughput garbage collector by using the
           -XX:+UseParallelGC and -XX:+UseParallelOldGC options, and survivor
           space is resized according to the application behavior, starting
           with the initial value. If adaptive sizing is disabled (using the
           -XX:-UseAdaptiveSizePolicy option), then the -XX:SurvivorRatio
           option should be used to set the size of the survivor space for the
           entire execution of the application.

           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):

               S=Y/(R+2)

           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.

           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.

           The following example shows how to set the initial survivor space
           ratio to 4:

               -XX:InitialSurvivorRatio=4


       -XX:InitiatingHeapOccupancyPercent=percent
           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).

           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%:

               -XX:InitiatingHeapOccupancyPercent=75


       -XX:MaxGCPauseMillis=time
           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.

           The following example shows how to set the maximum target pause
           time to 500 ms:

               -XX:MaxGCPauseMillis=500


       -XX:MaxHeapSize=size
           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 k or K to indicate kilobytes, m or M to indicate megabytes,
           g or G to indicate gigabytes. The default value is chosen at
           runtime based on system configuration. For server deployments,
           -XX:InitialHeapSize and -XX:MaxHeapSize are often set to the same
           value. See the section "Ergonomics" in Java SE HotSpot Virtual
           Machine Garbage Collection Tuning Guide at
           http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

           The following examples show how to set the maximum allowed size of
           allocated memory to 80 MB using various units:

               -XX:MaxHeapSize=83886080
               -XX:MaxHeapSize=81920k
               -XX:MaxHeapSize=80m

           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.

           The -XX:MaxHeapSize option is equivalent to -Xmx.

       -XX:MaxHeapFreeRatio=percent
           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%.

           The following example shows how to set the maximum free heap ratio
           to 75%:

               -XX:MaxHeapFreeRatio=75


       -XX:MaxMetaspaceSize=size
           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.

           The following example shows how to set the maximum class metadata
           size to 256 MB:

               -XX:MaxMetaspaceSize=256m


       -XX:MaxNewSize=size
           Sets the maximum size (in bytes) of the heap for the young
           generation (nursery). The default value is set ergonomically.

       -XX:MaxTenuringThreshold=threshold
           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.

           The following example shows how to set the maximum tenuring
           threshold to 10:

               -XX:MaxTenuringThreshold=10


       -XX:MetaspaceSize=size
           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.

       -XX:MinHeapFreeRatio=percent
           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%.

           The following example shows how to set the minimum free heap ratio
           to 25%:

               -XX:MinHeapFreeRatio=25


       -XX:NewRatio=ratio
           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:

               -XX:NewRatio=1


       -XX:NewSize=size
           Sets the initial size (in bytes) of the heap for the young
           generation (nursery). Append the letter k or K to indicate
           kilobytes, m or M to indicate megabytes, g or G to indicate
           gigabytes.

           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.

           The following examples show how to set the initial size of young
           generation to 256 MB using various units:

               -XX:NewSize=256m
               -XX:NewSize=262144k
               -XX:NewSize=268435456

           The -XX:NewSize option is equivalent to -Xmn.

       -XX:ParallelGCThreads=threads
           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.

           For example, to set the number of threads for parallel GC to 2,
           specify the following option:

               -XX:ParallelGCThreads=2


       -XX:+ParallelRefProcEnabled
           Enables parallel reference processing. By default, this option is
           disabled.

       -XX:+PrintAdaptiveSizePolicy
           Enables printing of information about adaptive generation sizing.
           By default, this option is disabled.

       -XX:+PrintGC
           Enables printing of messages at every GC. By default, this option
           is disabled.

       -XX:+PrintGCApplicationConcurrentTime
           Enables printing of how much time elapsed since the last pause (for
           example, a GC pause). By default, this option is disabled.

       -XX:+PrintGCApplicationStoppedTime
           Enables printing of how much time the pause (for example, a GC
           pause) lasted. By default, this option is disabled.

       -XX:+PrintGCDateStamps
           Enables printing of a date stamp at every GC. By default, this
           option is disabled.

       -XX:+PrintGCDetails
           Enables printing of detailed messages at every GC. By default, this
           option is disabled.

       -XX:+PrintGCTaskTimeStamps
           Enables printing of time stamps for every individual GC worker
           thread task. By default, this option is disabled.

       -XX:+PrintGCTimeStamps
           Enables printing of time stamps at every GC. By default, this
           option is disabled.

       -XX:+PrintStringDeduplicationStatistics
           Prints detailed deduplication statistics. By default, this option
           is disabled. See the -XX:+UseStringDeduplication option.

       -XX:+PrintTenuringDistribution
           Enables printing of tenuring age information. The following is an
           example of the output:

               Desired survivor size 48286924 bytes, new threshold 10 (max 10)
               - age 1: 28992024 bytes, 28992024 total
               - age 2: 1366864 bytes, 30358888 total
               - age 3: 1425912 bytes, 31784800 total
               ...

           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.

           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.

           By default, this option is disabled.

       -XX:+ScavengeBeforeFullGC
           Enables GC of the young generation before each full GC. This option
           is enabled by default. Oracle recommends that you do not 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 -XX:-ScavengeBeforeFullGC.

       -XX:SoftRefLRUPolicyMSPerMB=time
           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 -XX:SoftRefLRUPolicyMSPerMB 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 -Xmx option has a
           significant effect on how quickly soft references are garbage
           collected.

           The following example shows how to set the value to 2.5 seconds:

               -XX:SoftRefLRUPolicyMSPerMB=2500


       -XX:StringDeduplicationAgeThreshold=threshold
           String objects reaching the specified age are considered candidates
           for deduplication. An object's age is a measure of how many times
           it has survived garbage collection. This is sometimes referred to
           as tenuring; see the -XX:+PrintTenuringDistribution option. Note
           that String 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 3. See the
           -XX:+UseStringDeduplication option.

       -XX:SurvivorRatio=ratio
           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:

               -XX:SurvivorRatio=4


       -XX:TargetSurvivorRatio=percent
           Sets the desired percentage of survivor space (0 to 100) used after
           young garbage collection. By default, this option is set to 50%.

           The following example shows how to set the target survivor space
           ratio to 30%:

               -XX:TargetSurvivorRatio=30


       -XX:TLABSize=size
           Sets the initial size (in bytes) of a thread-local allocation
           buffer (TLAB). Append the letter k or K to indicate kilobytes, m or
           M to indicate megabytes, g or G to indicate gigabytes. If this
           option is set to 0, then the JVM chooses the initial size
           automatically.

           The following example shows how to set the initial TLAB size to 512
           KB:

               -XX:TLABSize=512k


       -XX:+UseAdaptiveSizePolicy
           Enables the use of adaptive generation sizing. This option is
           enabled by default. To disable adaptive generation sizing, specify
           -XX:-UseAdaptiveSizePolicy and set the size of the memory
           allocation pool explicitly (see the -XX:SurvivorRatio option).

       -XX:+UseCMSInitiatingOccupancyOnly
           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.

       -XX:+UseConcMarkSweepGC
           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 (-XX:+UseParallelGC) garbage collector. The G1
           garbage collector (-XX:+UseG1GC) is another alternative.

           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 -XX:+UseParNewGC option
           is automatically set and you should not disable it, because the
           following combination of options has been deprecated in JDK 8:
           -XX:+UseConcMarkSweepGC -XX:-UseParNewGC.

       -XX:+UseG1GC
           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).

           By default, this option is disabled and the collector is chosen
           automatically based on the configuration of the machine and type of
           the JVM.

       -XX:+UseGCOverheadLimit
           Enables the use of a policy that limits the proportion of time
           spent by the JVM on GC before an OutOfMemoryError exception is
           thrown. This option is enabled, by default and the parallel GC will
           throw an OutOfMemoryError 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
           -XX:-UseGCOverheadLimit.

       -XX:+UseNUMA
           Enables performance optimization of an application on a machine
           with nonuniform memory architecture (NUMA) by increasing the
           application's 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
           (-XX:+UseParallelGC).

       -XX:+UseParallelGC
           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.

           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 -XX:+UseParallelOldGC option is
           automatically enabled, unless you explicitly disable it.

       -XX:+UseParallelOldGC
           Enables the use of the parallel garbage collector for full GCs. By
           default, this option is disabled. Enabling it automatically enables
           the -XX:+UseParallelGC option.

       -XX:+UseParNewGC
           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 -XX:+UseConcMarkSweepGC
           option. Using the -XX:+UseParNewGC option without the
           -XX:+UseConcMarkSweepGC option was deprecated in JDK 8.

       -XX:+UseSerialGC
           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.

       -XX:+UseSHM
           On Linux, enables the JVM to use shared memory to setup large
           pages.

           For more information, see "Large Pages".

       -XX:+UseStringDeduplication
           Enables string deduplication. By default, this option is disabled.
           To use this option, you must enable the garbage-first (G1) garbage
           collector. See the -XX:+UseG1GC option.

           String deduplication reduces the memory footprint of String objects
           on the Java heap by taking advantage of the fact that many String
           objects are identical. Instead of each String object pointing to
           its own character array, identical String objects can point to and
           share the same character array.

       -XX:+UseTLAB
           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 -XX:-UseTLAB.

Deprecated and Removed Options

   Deprecated and Removed Options
       These options were included in the previous release, but have since
       been considered unnecessary.

       -Xincgc
           Enables incremental garbage collection. This option was deprecated
           in JDK 8 with no replacement.

       -Xrunlibname
           Loads the specified debugging/profiling library. This option was
           superseded by the -agentlib option.

       -XX:CMSIncrementalDutyCycle=percent
           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 -XX:+CMSIncrementalMode option.

       -XX:CMSIncrementalDutyCycleMin=percent
           Sets the percentage of time (0 to 100) between minor collections
           that is the lower bound for the duty cycle when
           -XX:+CMSIncrementalPacing is enabled. This option was deprecated in
           JDK 8 with no replacement, following the deprecation of the
           -XX:+CMSIncrementalMode option.

       -XX:+CMSIncrementalMode
           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 CMSIncremental.

       -XX:CMSIncrementalOffset=percent
           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
           -XX:+CMSIncrementalMode option.

       -XX:+CMSIncrementalPacing
           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 -XX:+CMSIncrementalMode option.

       -XX:CMSIncrementalSafetyFactor=percent
           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
           -XX:+CMSIncrementalMode option.

       -XX:CMSInitiatingPermOccupancyFraction=percent
           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.

       -XX:MaxPermSize=size
           Sets the maximum permanent generation space size (in bytes). This
           option was deprecated in JDK 8, and superseded by the
           -XX:MaxMetaspaceSize option.

       -XX:PermSize=size
           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 -XX:MetaspaceSize
           option.

       -XX:+UseSplitVerifier
           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.

       -XX:+UseStringCache
           Enables caching of commonly allocated strings. This option was
           removed from JDK 8 with no replacement.

PERFORMANCE TUNING EXAMPLES

PERFORMANCE TUNING EXAMPLES
       The following examples show how to use experimental tuning flags to
       either optimize throughput or to provide lower response time.

       Example 1 Tuning for Higher Throughput

               java -d64 -server -XX:+AggressiveOpts -XX:+UseLargePages -Xmn10g  -Xms26g -Xmx26g


       Example 2 Tuning for Lower Response Time

               java -d64 -XX:+UseG1GC -Xms26g Xmx26g -XX:MaxGCPauseMillis=500 -XX:+PrintGCTimeStamp

LARGE PAGES

LARGE PAGES
       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.

       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.

       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.

Large Pages Support

   Large Pages Support
       Solaris and Linux support large pages.

       Solaris
           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.

       Linux
           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:

               # cat /proc/meminfo | grep Huge
               HugePages_Total: 0
               HugePages_Free: 0
               Hugepagesize: 2048 kB


           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
           root, and then follow these steps:

            1. If you are using the option -XX:+UseSHM (instead of
               -XX:+UseHugeTLBFS), then increase the SHMMAX 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:

                   # echo 4294967295 > /proc/sys/kernel/shmmax


            2. If you are using the option -XX:+UseSHM or -XX:+UseHugeTLBFS,
               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):

                   # echo 1536 > /proc/sys/vm/nr_hugepages


               Note
               ┌──────────────────────────────────────────────┐
               │                                              │
               │               ·   Note that the values       │
               │                   contained in /proc         │
               │                   will reset after you       │
               │                   reboot your system,        │
               │                   so may want to set         │
               │                   them in an                 │
               │                   initialization             │
               │                   script (for example,       │
               │                   rc.local or                │
               │                   sysctl.conf).              │
               │                                              │
               │               ·   If you configure (or       │
               │                   resize) the OS             │
               │                   kernel parameters          │
               │                   /proc/sys/kernel/shmmax    │
               │                   or                         │
               │                   /proc/sys/vm/nr_hugepages, │
               │                   Java processes may         │
               │                   allocate large pages       │
               │                   for areas in               │
               │                   addition to the Java       │
               │                   heap. These steps          │
               │                   can allocate large         │
               │                   pages for the              │
               │                   following areas:           │
               │                                              │
               │                   ·   Java heap              │
               │                                              │
               │                   ·   Code cache             │
               │                                              │
               │                   ·   The marking            │
               │                       bitmap data            │
               │                       structure for          │
               │                       the parallel GC        │
               │                                              │
               │                   Consequently, if you       │
               │                   configure the              │
               │                   nr_hugepages               │
               │                   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.             │
               └──────────────────────────────────────────────┘

APPLICATION CLASS DATA SHARING

APPLICATION CLASS DATA SHARING
       Application Class Data Sharing (AppCDS) extends CDS (see
       https://docs.oracle.com/javase/8/docs/technotes/guides/vm/class-data-sharing.html)
       to enable classes from the standard extensions directories (specified
       by the system property java.ext.dirs; see
       https://docs.oracle.com/javase/8/docs/technotes/guides/extensions/spec.html)
       and the application class path (see "Setting the Class Path ") to be
       placed in the shared archive. AppCDS reduces the footprint and
       decreases start-up time of your applications provided that a
       substantial number of classes are loaded from the application class
       path.

       This is a commercial feature that requires you to also specify the
       -XX:+UnlockCommercialFeatures option. This is also an experimental
       feature; it may change in future releases.

   Creating a Shared Archive File, and Running an Application with It
       The following steps create a shared archive file that contains all the
       classes used by the test.Hello application. The last step runs the
       application with the shared archive file.

        1. Create a list of all classes used by the test.Hello application.
           The following command creates a file named hello.classlist that
           contains a list of all classes used by this application:

           java -Xshare:off -XX:+UnlockCommercialFeatures
           -XX:DumpLoadedClassList=hello.classlist -XX:+UseAppCDS -cp
           hello.jar test.Hello

           Note that the -cp parameter must contain only JAR files; the
           -XX:+UseAppCDS option does not support class paths that contain
           directory names.

        2. Create a shared archive, named hello.jsa, that contains all the
           classes in hello.classlist:

           java -XX:+UnlockCommercialFeatures -Xshare:dump -XX:+UseAppCDS
           -XX:SharedArchiveFile=hello.jsa
           -XX:SharedClassListFile=hello.classlist -cp hello.jar

           Note that the -cp parameter used at archive creation time must be
           the same as (or a prefix of) the -cp used at run time.

        3. Run the application test.Hello with the shared archive hello.jsa:

           java -XX:+UnlockCommercialFeatures -Xshare:on -XX:+UseAppCDS
           -XX:SharedArchiveFile=hello.jsa -cp hello.jar test.Hello

           Ensure that you have specified the option -Xshare:on or
           -Xshare:auto.

        4. Verify that the test.Hello application is using the class contained
           in the hello.jsa shared archive:

           java -XX:+UnlockCommercialFeatures -Xshare:on -XX:+UseAppCDS
           -XX:SharedArchiveFile=hello.jsa -cp hello.jar -verbose:class
           test.Hello

           The output of this command should contain the following text:

           Loaded test.Hello from shared objects file by
           sun/misc/Launcher$AppClassLoader

   Sharing a Shared Archive across Multiple Application Processes
       You can share the same archive file across multiple applications
       processes that have the exact same class path or share a common class
       path prefix. This reduces memory usage as the archive is memory-mapped
       into the address space of the processes. The operating system
       automatically shares the read-only pages across these processes.

       The following steps create a shared archive that both applications
       Hello and Hi can use.

        1. Create a list of all classes used by the Hello application and
           another list for the Hi application:

           java -XX:+UnlockCommercialFeatures
           -XX:DumpLoadedClassList=hello.classlist -XX:+UseAppCDS -cp
           common.jar:hello.jar Hello

           java -XX:+UnlockCommercialFeatures
           -XX:DumpLoadedClassList=hi.classlist -XX:+UseAppCDS -cp
           common.jar:hi.jar Hi

           Note that because the Hello and Hi applications share a common
           class path prefix (both of their class paths start with
           common.jar), these two applications can share a shared archive
           file.

        2. Create a single list of classes used by all the applications that
           will share the shared archive file.

           The following commands combine the files hello.classlist and
           hi.classlist to one file, common.classlist:

           cat hello.classlist hi.classlist > common.classlist

        3. Create a shared archive, named common.jsa, that contains all the
           classes in common.classlist:

           java -XX:+UnlockCommercialFeatures -Xshare:dump
           -XX:SharedArchiveFile=common.jsa -XX:+UseAppCDS
           -XX:SharedClassListFile=common.classlist -cp common.jar

           The value of the -cp parameter is the common class path prefix
           shared by the Hello and Hi applications.

        4. Run the Hello and Hi applications with the same shared archive:

           java -XX:+UnlockCommercialFeatures -Xshare:on
           -XX:SharedArchiveFile=common.jsa -XX:+UseAppCDS -cp
           common.jar:hello.jar Hello

           java -XX:+UnlockCommercialFeatures -Xshare:on
           -XX:SharedArchiveFile=common.jsa -XX:+UseAppCDS -cp
           common.jar:hi.jar Hi

EXIT STATUS
       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 System.exit(exitValue). The
       values are:

       ·   0: Successful completion

       ·   >0: An error occurred

SEE ALSO
       ·   javac(1)

       ·   jdb(1)

       ·   javah(1)

       ·   jar(1)

       ·   jstat(1)



JDK 8                            03 March 2015                         java(1)

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