jvm参数设置

This document provides information on typical command-line options andenvironment variables that can affect the performance characteristicsof the Java HotSpot Virtual Machine. Unless otherwise noted, allinformation in this document pertains to both the Java HotSpot ClientVM 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 (notguaranteed to be supported on all VM implementations), and are subjectto 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 adiffering 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 writeablethrough the JDK management interface(com.sun.management.HotSpotDiagnosticMXBean API) and also throughJConsole. 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

 

Option and Default Value
Description-XX:-AllowUserSignalHandlersDo not complain if the application installs signal handlers. (Relevant to Solaris and Linux only.)

-XX:AltStackSize=16384Alternate signal stack size (in Kbytes). (Relevant to Solaris only, removed from 5.0.)

-XX:-DisableExplicitGCDisable calls to System.gc(), JVM still performs garbage collection when necessary.

-XX:+FailOverToOldVerifierFail over to old verifier when the new type checker fails. (Introduced in 6.)

-XX:+HandlePromotionFailureThe youngest generation collection does not require a guarantee of full promotion of all live objects. (Introduced in 1.4.2update 11) [5.0 and earlier: false.]

-XX:+MaxFDLimitBump the number of file descriptors to max. (Relevant to Solaris only.)

-XX:PreBlockSpin=10Spin count variable for use with -XX:+UseSpinning. Controls themaximum spin iterations allowed before entering operating system threadsynchronization code. (Introduced in 1.4.2.)

-XX:-RelaxAccessControlCheckRelax the access control checks in the verifier. (Introducedin 6.)

-XX:+ScavengeBeforeFullGCDo young generation GC prior to a full GC. (Introduced in 1.4.1.)

-XX:+UseAltSigsUse alternate signals instead of SIGUSR1 and SIGUSR2 for VMinternal signals. (Introduced in 1.3.1 update 9, 1.4.1. Relevant toSolaris only.)

-XX:+UseBoundThreadsBind user level threads to kernel threads. (Relevant toSolaris only.)

-XX:-UseConcMarkSweepGCUse concurrent mark-sweep collection for the old generation.(Introduced in 1.4.1)

-XX:+UseGCOverheadLimitUse a policy that limits the proportion of the VM's time that isspent in GC before an OutOfMemory error is thrown. (Introduced in 6.)

-XX:+UseLWPSynchronizationUse LWP-based instead of thread based synchronization. (Introduced in 1.4.0. Relevant to Solaris only.)

-XX:-UseParallelGCUse parallel garbage collection for scavenges. (Introduced in 1.4.1)

-XX:-UseParallelOldGCUse parallel garbage collection for the full collections. Enablingthis option automatically sets -XX:+UseParallelGC. (Introduced in 5.0update 6.)

-XX:-UseSerialGCUse serial garbage collection. (Introduced in 5.0.)

-XX:-UseSpinningEnable naive spinning on Java monitor before entering operatingsystem thread synchronizaton code. (Relevant to 1.4.2 and 5.0 only.)[1.4.2, multi-processor Windows platforms: true]

-XX:+UseTLABUse thread-local object allocation (Introduced in 1.4.0, known asUseTLE prior to that.) [1.4.2 and earlier, x86 or with -client: false]

-XX:+UseSplitVerifierUse the newtype checker with StackMapTable attributes. (Introduced in 5.0.)[5.0: false]

-XX:+UseThreadPrioritiesUse native thread priorities.

-XX:+UseVMInterruptibleIOThread interrupt before or with EINTR for I/O operations results in OS_INTRPT. (Introduced in 6. Relevant to Solaris only.)

---

Performance Options

 

Option and Default Value
Description-XX:+AggressiveOptsTurn on point performance compiler optimizations that are expectedto 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 iscomputed 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); Sparc64 bit: 1024; Linux amd64: 1024 (was 0 in 5.0 and earlier); allothers 0.]

-XX:+UseBiasedLockingEnable biased locking. For more details, see this tuningexample. (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-Solarisplatforms.] For details, see Intimate Shared Memory.

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

-XX:+UseMPSSUse Multiple Page Size Support w/4mb pages for the heap. Do not usewith ISM as this replaces the need for ISM. (Introduced in 1.4.0 update1, Relevant to Solaris 9 and newer.) [1.4.1and earlier: false]

-XX:+StringCacheEnables caching of commonly allocated strings.

-XX:AllocatePrefetchLines=1Number of cache lines to load after the last object allocationusing prefetch instructions generated in JIT compiled code. Defaultvalues are 1 if the last allocated object was an instance and 3 if itwas 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.

 

---

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 in1.4.2 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.