VM parameter

Behavioral Options

 

Option and Default Value	Description
-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:+AggressiveOpts	Turn on point performance compiler optimizations that are expected to be default in upcoming releases. (Introduced in 5.0 update 6.)
-XX:CompileThreshold=10000	Number of method invocations/branches before compiling [-client: 1,500]
-XX:LargePageSizeInBytes=4m	Sets the large page size used for the Java heap. (Introduced in 1.4.0 update 1.) [amd64: 2m.]
-XX:MaxHeapFreeRatio=70	Maximum percentage of heap free after GC to avoid shrinking.
-XX:MaxNewSize=size	Maximum 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=64m	Size 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=40	Minimum 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=32m	Reserved 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=8	enden 和每一个survivor的比例，以此为列，比例为8：1
-XX:TargetSurvivorRatio=50	Desired percentage of survivor space used after scavenge.
-XX:ThreadStackSize=512	每个线程使用VM stack 的大小
-XX:+UseBiasedLocking	Enable biased locking. For more details, see this tuning example . (Introduced in 5.0 update 6.) [5.0: false]
-XX:+UseFastAccessorMethods	Use optimized versions of Get<Primitive>Field.
-XX:-UseISM	Use Intimate Shared Memory. [Not accepted for non-Solaris platforms.] For details, see Intimate Shared Memory .
-XX:+UseLargePages	Use large page memory. (Introduced in 5.0 update 5.) For details, see Java Support for Large Memory Pages .
-XX:+UseMPSS	Use 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:+UseStringCache	Enables caching of commonly allocated strings.
-XX:AllocatePrefetchLines=1	Number 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=1	Generated 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:+UseCompressedStrings	Use a byte[] for Strings which can be represented as pure ASCII. (Introduced in Java 6 Update 21 Performance Release)
-XX:+OptimizeStringConcat	Optimize String concatenation operations where possible. (Introduced in Java 6 Update 20)

Back to Options
 

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Debugging Options

 

Option and Default Value	Description
-XX:-CITime	Prints time spent in JIT Compiler. (Introduced in 1.4.0.)
-XX:ErrorFile=./hs_err_pid<pid>.log	If an error occurs, save the error data to this file. (Introduced in 6.)
-XX:-ExtendedDTraceProbes	Enable performance-impacting dtrace probes. (Introduced in 6. Relevant to Solaris only.)
-XX:HeapDumpPath=./java_pid<pid>.hprof	Path to directory or filename for heap dump. Manageable . (Introduced in 1.4.2 update 12, 5.0 update 7.)
-XX:-HeapDumpOnOutOfMemoryError	Dump 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:-PrintClassHistogram	Print a histogram of class instances on Ctrl-Break. Manageable . (Introduced in 1.4.2.) The jmap -histo command provides equivalent functionality.
-XX:-PrintConcurrentLocks	Print 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:-PrintCommandLineFlags	Print flags that appeared on the command line. (Introduced in 5.0.)
-XX:-PrintCompilation	Print message when a method is compiled.
-XX:-PrintGC	Print messages at garbage collection. Manageable .
-XX:-PrintGCDetails	Print more details at garbage collection. Manageable . (Introduced in 1.4.0.)
-XX:-PrintGCTimeStamps	Print timestamps at garbage collection. Manageable (Introduced in 1.4.0.)
-XX:-PrintTenuringDistribution	Print tenuring age information.
-XX:-TraceClassLoading	Trace loading of classes.
-XX:-TraceClassLoadingPreorder	Trace all classes loaded in order referenced (not loaded). (Introduced in 1.4.2.)
-XX:-TraceClassResolution	Trace constant pool resolutions. (Introduced in 1.4.2.)
-XX:-TraceClassUnloading	Trace unloading of classes.
-XX:-TraceLoaderConstraints	Trace recording of loader constraints. (Introduced in 6.)
-XX:+PerfSaveDataToFile	Saves jvmstat binary data on exit.