SUN JVM 参数权威指南

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<div class="d7"><div class="d7v9"><div class="cornerBL"><div class="cornerBR"><!--StartFragment-->This document provides information on typical command-line options and environment variables that can affect the performance characteristics of the Java HotSpot Virtual Machine. Unless otherwise noted, all information in this document pertains to both the Java HotSpot Client VM and the Java HotSpot Server VM. Users of JDKs older than 1.3.0 who wish to port to a Java HotSpot VM, should see Java HotSpot Equivalents of Exact VM flags.   Categories of Java HotSpot VM Options   Standard options recognized by the Java HotSpot VM are described on the Java Application Launcher reference pages for Windows, Solaris and Linux. This document deals exclusively with non-standard options recognized by the Java HotSpot VM: Options that begin with -X are non-standard (not guaranteed to be supported on all VM implementations), and are subject to change without notice in subsequent releases of the JDK. Options that are specified with -XX are not stable and are not recommended for casual use. These options are subject to change without notice.   Some Useful -XX Options   Default values are listed for Java SE 6 for Solaris Sparc with -server. Some options may vary per architecture/OS/JVM version. Platforms with a differing default value are listed in the description. Boolean options are turned on with -XX:+<option> and turned off with -XX:-<option>. Numeric options are set with -XX:<option>=<number>. Numbers can include 'm' or 'M' for megabytes, 'k' or 'K' for kilobytes, and 'g' or 'G' for gigabytes (for example, 32k is the same as 32768). String options are set with -XX:<option>=<string>, are usually used to specify a file, a path, or a list of commands Flags marked as manageable are dynamically writeable through the JDK management interface (com.sun.management.HotSpotDiagnosticMXBean API) and also through JConsole. In Monitoring and Managing Java SE 6 Platform Applications, Figure 3 shows an example. The manageable flags can also be set through jinfo -flag. The options below are loosely grouped into three categories. Behavioral options change the basic behavior of the VM. Performance tuning options are knobs which can be used to tune VM performance. Debugging options generally enable tracing, printing, or output of VM information.   Behavioral Options [table=98%][tr]Option and Default Value Description[/tr]
-XX:-AllowUserSignalHandlers	Do not complain if the application installs signal handlers. (Relevant to Solaris and Linux only.)
-XX:AltStackSize=16384	Alternate signal stack size (in Kbytes). (Relevant to Solaris only, removed from 5.0.)
-XX:-DisableExplicitGC	Disable calls to System.gc(), JVM still performs garbage collection when necessary.
-XX:+FailOverToOldVerifier	Fail over to old verifier when the new type checker fails. (Introduced in 6.)
-XX:+HandlePromotionFailure	The youngest generation collection does not require a guarantee of full promotion of all live objects. (Introduced in 1.4.2 update 11) [5.0 and earlier: false.]
-XX:+MaxFDLimit	Bump the number of file descriptors to max. (Relevant  to Solaris only.)
-XX:PreBlockSpin=10	Spin count variable for use with -XX:+UseSpinning. Controls the maximum spin iterations allowed before entering operating system thread synchronization code. (Introduced in 1.4.2.)
-XX:-RelaxAccessControlCheck	Relax the access control checks in the verifier. (Introduced in 6.)
-XX:+ScavengeBeforeFullGC	Do young generation GC prior to a full GC. (Introduced in 1.4.1.)
-XX:+UseAltSigs	Use alternate signals instead of SIGUSR1 and SIGUSR2 for VM internal signals. (Introduced in 1.3.1 update 9, 1.4.1. Relevant to Solaris only.)
-XX:+UseBoundThreads	Bind user level threads to kernel threads. (Relevant to Solaris only.)
-XX:-UseConcMarkSweepGC	Use concurrent mark-sweep collection for the old generation. (Introduced in 1.4.1)
-XX:+UseGCOverheadLimit	Use a policy that limits the proportion of the VM's time that is spent in GC before an OutOfMemory error is thrown. (Introduced in 6.)
-XX:+UseLWPSynchronization	Use LWP-based instead of thread based synchronization. (Introduced in 1.4.0. Relevant to Solaris only.)
-XX:-UseParallelGC	Use parallel garbage collection for scavenges. (Introduced in 1.4.1)
-XX:-UseParallelOldGC	Use parallel garbage collection for the full collections. Enabling this option automatically sets -XX:+UseParallelGC. (Introduced in 5.0 update 6.)
-XX:-UseSerialGC	Use serial garbage collection. (Introduced in 5.0.)
-XX:-UseSpinning	Enable naive spinning on Java monitor before entering operating system thread synchronizaton code. (Relevant to 1.4.2 and 5.0 only.) [1.4.2, multi-processor Windows platforms: true]
-XX:+UseTLAB	Use thread-local object allocation (Introduced in 1.4.0, known as UseTLE prior to that.) [1.4.2 and earlier, x86 or with -client: false]
-XX:+UseSplitVerifier	Use the new type checker with StackMapTable attributes. (Introduced in 5.0.)[5.0: false]
-XX:+UseThreadPriorities	Use native thread priorities.
-XX:+UseVMInterruptibleIO	Thread interrupt before or with EINTR for I/O operations results in OS_INTRPT. (Introduced in 6. Relevant to Solaris only.)

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Performance Options


Option and Default Value
Description-XX:+AggressiveOptsTurn on point performance compiler optimizations that are expected to be default in upcoming releases. (Introduced in 5.0 update 6.)

-XX:CompileThreshold=10000Number of method invocations/branches before compiling [-client: 1,500]

-XX:LargePageSizeInBytes=4mSets the large page size used for the Java heap. (Introduced in 1.4.0 update 1.) [amd64: 2m.]

-XX:MaxHeapFreeRatio=70Maximum percentage of heap free after GC to avoid shrinking.

-XX:MaxNewSize=sizeMaximum size of new generation (in bytes). Since 1.4, MaxNewSize is computed as a function of NewRatio. [1.3.1 Sparc: 32m; 1.3.1 x86: 2.5m.]

-XX:MaxPermSize=64mSize of the Permanent Generation.  [5.0 and newer: 64 bit VMs are scaled 30% larger; 1.4 amd64: 96m; 1.3.1 -client: 32m.]

-XX:MinHeapFreeRatio=40Minimum percentage of heap free after GC to avoid expansion.

-XX:NewRatio=2Ratio of new/old generation sizes. [Sparc -client: 8; x86 -server: 8; x86 -client: 12.]-client: 4 (1.3) 8 (1.3.1+), x86: 12]

-XX:NewSize=2.125mDefault size of new generation (in bytes) [5.0 and newer: 64 bit VMs are scaled 30% larger; x86: 1m; x86, 5.0 and older: 640k]

-XX:ReservedCodeCacheSize=32mReserved code cache size (in bytes) - maximum code cache size. [Solaris 64-bit, amd64, and -server x86: 48m; in 1.5.0_06 and earlier, Solaris 64-bit and and64: 1024m.]

-XX:SurvivorRatio=8Ratio of eden/survivor space size [Solaris amd64: 6; Sparc in 1.3.1: 25; other Solaris platforms in 5.0 and earlier: 32]

-XX:TargetSurvivorRatio=50Desired percentage of survivor space used after scavenge.

-XX:ThreadStackSize=512Thread Stack Size (in Kbytes). (0 means use default stack size) [Sparc: 512; Solaris x86: 320 (was 256 prior in 5.0 and earlier); Sparc 64 bit: 1024; Linux amd64: 1024 (was 0 in 5.0 and earlier); all others 0.]

-XX:+UseBiasedLockingEnable biased locking. For more details, see this tuning example. (Introduced in 5.0 update 6.) [5.0: false]

-XX:+UseFastAccessorMethodsUse optimized versions of Get<Primitive>Field.

-XX:-UseISMUse Intimate Shared Memory. [Not accepted for non-Solaris platforms.] For details, see Intimate Shared Memory.

-XX:+UseLargePagesUse large page memory. (Introduced in 5.0 update 5.) For details, see Java Support for Large Memory Pages.

-XX:+UseMPSSUse Multiple Page Size Support w/4mb pages for the heap. Do not use with ISM as this replaces the need for ISM. (Introduced in 1.4.0 update 1, Relevant to Solaris 9 and newer.) [1.4.1 and earlier: false]

-XX:+StringCacheEnables caching of commonly allocated strings.

-XX:AllocatePrefetchLines=1Number of cache lines to load after the last object allocation using prefetch instructions generated in JIT compiled code. Default values are 1 if the last allocated object was an instance and 3 if it was an array.

-XX:AllocatePrefetchStyle=1Generated code style for prefetch instructions.
0 - no prefetch instructions are generate*d*,
1 - execute prefetch instructions after each allocation,
2 - use TLAB allocation watermark pointer to gate when prefetch instructions are executed.


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Debugging Options


Option and Default Value
Description-XX:-CITimePrints time spent in JIT Compiler. (Introduced in 1.4.0.)

-XX:ErrorFile=./hs_err_pid<pid>.logIf an error occurs, save the error data to this file. (Introduced in 6.)

-XX:-ExtendedDTraceProbesEnable performance-impacting dtrace probes. (Introduced in 6. Relevant to Solaris only.)

-XX:HeapDumpPath=./java_pid<pid>.hprofPath to directory or filename for heap dump. Manageable. (Introduced in 1.4.2 update 12, 5.0 update 7.)

-XX:-HeapDumpOnOutOfMemoryErrorDump heap to file when java.lang.OutOfMemoryError is thrown. Manageable. (Introduced in 1.4.2 update 12, 5.0 update 7.)

-XX:OnError="<cmd args>;<cmd args>"Run user-defined commands on fatal error. (Introduced in 1.4.2 update 9.)

-XX:OnOutOfMemoryError="<cmd args>;
<cmd args>"Run user-defined commands when an OutOfMemoryError is first thrown. (Introduced in 1.4.2 update 12, 6)

-XX:-PrintClassHistogramPrint a histogram of class instances on Ctrl-Break. Manageable. (Introduced in 1.4.2.) The jmap -histo command provides equivalent functionality.

-XX:-PrintConcurrentLocksPrint java.util.concurrent locks in Ctrl-Break thread dump. Manageable. (Introduced in 6.) The jstack -l command provides equivalent functionality.

-XX:-PrintCommandLineFlagsPrint flags that appeared on the command line. (Introduced in 5.0.)

-XX:-PrintCompilationPrint message when a method is compiled.

-XX:-PrintGCPrint messages at garbage collection. Manageable.

-XX:-PrintGCDetailsPrint more details at garbage collection. Manageable. (Introduced in 1.4.0.)

-XX:-PrintGCTimeStampsPrint timestamps at garbage collection. Manageable (Introduced in 1.4.0.)

-XX:-PrintTenuringDistributionPrint tenuring age information.

-XX:-TraceClassLoadingTrace loading of classes.

-XX:-TraceClassLoadingPreorderTrace all classes loaded in order referenced (not loaded). (Introduced in 1.4.2.)

-XX:-TraceClassResolutionTrace constant pool resolutions. (Introduced in 1.4.2.)

-XX:-TraceClassUnloadingTrace unloading of classes.

-XX:-TraceLoaderConstraintsTrace recording of loader constraints. (Introduced in 6.)

-XX:+PerfSaveDataToFileSaves jvmstat binary data on exit.

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