Some Useful -XX Options
- 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
Behavioral Options
Option and Default Value
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Description
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-XX:-AllowUserSignalHandlers
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Do not complain if the application installs signal handlers. (Relevant to Solaris and Linux only.)
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-XX:AltStackSize=16384
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Alternate signal stack size (in Kbytes). (Relevant to Solaris only, removed from 5.0.)
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-XX:-DisableExplicitGC
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Disable calls to System.gc(), JVM still performs garbage collection when necessary.
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-XX:+FailOverToOldVerifier
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Fail over to old verifier when the new type checker fails. (Introduced in 6.)
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-XX:+HandlePromotionFailure
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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.]
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-XX:+MaxFDLimit
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Bump the number of file descriptors to max. (Relevant to Solaris only.)
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-XX:PreBlockSpin=10
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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.)
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-XX:-RelaxAccessControlCheck
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Relax the access control checks in the verifier. (Introduced in 6.)
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-XX:+ScavengeBeforeFullGC
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Do young generation GC prior to a full GC. (Introduced in 1.4.1.)
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-XX:+UseAltSigs
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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.)
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-XX:+UseBoundThreads
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Bind user level threads to kernel threads. (Relevant to Solaris only.)
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-XX:-UseConcMarkSweepGC
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Use concurrent mark-sweep collection for the old generation. (Introduced in 1.4.1)
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-XX:+UseGCOverheadLimit
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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.)
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-XX:+UseLWPSynchronization
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Use LWP-based instead of thread based synchronization. (Introduced in 1.4.0. Relevant to Solaris only.)
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-XX:-UseParallelGC
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Use parallel garbage collection for scavenges. (Introduced in 1.4.1)
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-XX:-UseParallelOldGC
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Use parallel garbage collection for the full collections. Enabling this option automatically sets -XX:+UseParallelGC. (Introduced in 5.0 update 6.)
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-XX:-UseSerialGC
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Use serial garbage collection. (Introduced in 5.0.)
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-XX:-UseSpinning
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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]
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-XX:+UseTLAB
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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]
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-XX:+UseSplitVerifier
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Use the new type checker with StackMapTable attributes. (Introduced in 5.0.)[5.0: false]
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-XX:+UseThreadPriorities
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Use native thread priorities.
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-XX:+UseVMInterruptibleIO
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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
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Description
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-XX:+AggressiveOpts
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Turn on point performance compiler optimizations that are expected to be default in upcoming releases. (Introduced in 5.0 update 6.)
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-XX:CompileThreshold=10000
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Number of method invocations/branches before compiling [-client: 1,500]
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-XX:LargePageSizeInBytes=4m
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Sets the large page size used for the Java heap. (Introduced in 1.4.0 update 1.) [amd64: 2m.]
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-XX:MaxHeapFreeRatio=70
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Maximum percentage of heap free after GC to avoid shrinking.
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-XX:MaxNewSize=size
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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.]
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-XX:MaxPermSize=64m
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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.]
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-XX:MinHeapFreeRatio=40
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Minimum percentage of heap free after GC to avoid expansion.
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-XX:NewRatio=2
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Ratio of new/old generation sizes. [Sparc -client: 8; x86 -server: 8; x86 -client: 12.]-client: 4 (1.3) 8 (1.3.1+), x86: 12]
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-XX:NewSize=2.125m
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Default 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]
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-XX:ReservedCodeCacheSize=32m
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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.]
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-XX:SurvivorRatio=8
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Ratio of eden/survivor space size [Solaris amd64: 6; Sparc in 1.3.1: 25; other Solaris platforms in 5.0 and earlier: 32]
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-XX:TargetSurvivorRatio=50
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Desired percentage of survivor space used after scavenge.
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-XX:ThreadStackSize=512
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Thread 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.]
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-XX:+UseBiasedLocking
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Enable biased locking. For more details, see thistuning example. (Introduced in 5.0 update 6.) [5.0: false]
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-XX:+UseFastAccessorMethods
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Use optimized versions of Get<Primitive>Field.
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-XX:-UseISM
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Use Intimate Shared Memory. [Not accepted for non-Solaris platforms.] For details, see Intimate Shared Memory.
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-XX:+UseLargePages
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Use large page memory. (Introduced in 5.0 update 5.) For details, see Java Support for Large Memory Pages.
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-XX:+UseMPSS
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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]
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-XX:+StringCache
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Enables caching of commonly allocated strings.
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-XX:AllocatePrefetchLines=1
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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.
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-XX:AllocatePrefetchStyle=1
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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. |
Debugging Options
Option and Default Value
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Description
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-XX:-CITime
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Prints time spent in JIT Compiler. (Introduced in 1.4.0.)
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-XX:ErrorFile=./hs_err_pid<pid>.log
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If an error occurs, save the error data to this file. (Introduced in 6.)
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-XX:-ExtendedDTraceProbes
| |
-XX:HeapDumpPath=./java_pid<pid>.hprof
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Path to directory or filename for heap dump.Manageable. (Introduced in 1.4.2 update 12, 5.0 update 7.)
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-XX:-HeapDumpOnOutOfMemoryError
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Dump heap to file when java.lang.OutOfMemoryError is thrown. Manageable. (Introduced in 1.4.2 update 12, 5.0 update 7.)
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-XX:OnError="<cmd args>;<cmd args>"
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Run user-defined commands on fatal error. (Introduced in 1.4.2 update 9.)
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-XX:OnOutOfMemoryError="<cmd args>;
<cmd args>" |
Run user-defined commands when an OutOfMemoryError is first thrown. (Introduced in 1.4.2 update 12, 6)
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-XX:-PrintClassHistogram
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Print a histogram of class instances on Ctrl-Break.Manageable. (Introduced in 1.4.2.) The jmap -histocommand provides equivalent functionality.
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-XX:-PrintConcurrentLocks
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Print java.util.concurrent locks in Ctrl-Break thread dump. Manageable. (Introduced in 6.) The jstack -lcommand provides equivalent functionality.
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-XX:-PrintCommandLineFlags
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Print flags that appeared on the command line. (Introduced in 5.0.)
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-XX:-PrintCompilation
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Print message when a method is compiled.
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-XX:-PrintGC
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Print messages at garbage collection. Manageable.
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-XX:-PrintGCDetails
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Print more details at garbage collection. Manageable. (Introduced in 1.4.0.)
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-XX:-PrintGCTimeStamps
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Print timestamps at garbage collection. Manageable(Introduced in 1.4.0.)
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-XX:-PrintTenuringDistribution
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Print tenuring age information.
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-XX:-TraceClassLoading
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Trace loading of classes.
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-XX:-TraceClassLoadingPreorder
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Trace all classes loaded in order referenced (not loaded). (Introduced in 1.4.2.)
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-XX:-TraceClassResolution
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Trace constant pool resolutions. (Introduced in 1.4.2.)
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-XX:-TraceClassUnloading
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Trace unloading of classes.
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-XX:-TraceLoaderConstraints
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Trace recording of loader constraints. (Introduced in 6.)
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-XX:+PerfSaveDataToFile
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Saves jvmstat binary data on exit.
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