VM parameter
Behavioral OptionsOption 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 1.4.2 update 11) -XX:+MaxFDLimitBump the number of file descriptors to max. (Relevant to Solaris only.)-XX:PreBlockSpin=10Spin 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:-RelaxAccessControlCheckRelax the access control checks in the verifier. (Introduced in 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 VM internal signals. (Introduced in 1.3.1 update 9, 1.4.1. Relevant to Solaris only.)-XX:+UseBoundThreadsBind user level threads to kernel threads. (Relevant to Solaris 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 is spent 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. Enabling this option automatically sets -XX:+UseParallelGC. (Introduced in 5.0 update 6.)-XX:-UseSerialGCUse serial garbage collection. (Introduced in 5.0.)-XX:-UseSpinningEnable naive spinning on Java monitor before entering operating system thread synchronizaton code. (Relevant to 1.4.2 and 5.0 only.) -XX:+UseTLABUse thread-local object allocation (Introduced in 1.4.0, known as UseTLE prior to that.) -XX:+UseSplitVerifierUse the new type checker with StackMapTable attributes. (Introduced in 5.0.)-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 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.) -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. -XX:MaxPermSize=64mSize of the Permanent Generation. -XX:MinHeapFreeRatio=40Minimum percentage of heap free after GC to avoid expansion.-XX:NewRatio=2这个是指new gen 和 old gen 的比例 如果总的内存是20m 那么 new gen 是 20*1/3
-XX:NewSize=2.125m这个是指new gen 的大小，试用其可以覆盖 NewRatio参数
-XX:ReservedCodeCacheSize=32mReserved code cache size (in bytes) - maximum code cache size. -XX:SurvivorRatio=8enden 和每一个survivor的比例，以此为列，比例为8：1
-XX:TargetSurvivorRatio=50Desired percentage of survivor space used after scavenge.-XX:ThreadStackSize=512每个线程使用VM stack 的大小-XX:+UseBiasedLockingEnable biased locking. For more details, see this tuning example. (Introduced in 5.0 update 6.) -XX:+UseFastAccessorMethodsUse optimized versions of Get<Primitive>Field.-XX:-UseISMUse Intimate Shared Memory. 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.) -XX:+UseStringCacheEnables 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.
-XX:-XX:+UseCompressedStringsUse a byte[] for Strings which can be represented as pure ASCII. (Introduced in Java 6 Update 21 Performance Release)
-XX:+OptimizeStringConcatOptimize String concatenation operations where possible.(Introduced in Java 6 Update 20)
Back to Options
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.
使用concurrent包时可以用来查看线程死锁
-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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