Thursday, November 18, 2010

Java HotSpot VM Options


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
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.)

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
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]
-XX:NewSize=2.125m
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]
-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
Ratio 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=50
Desired percentage of survivor space used after scavenge.
-XX:ThreadStackSize=512
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.]
-XX:+UseBiasedLocking
Enable biased locking. For more details, see thistuning 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:+StringCache
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.

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 -histocommand provides equivalent functionality.
-XX:-PrintConcurrentLocks
Print java.util.concurrent locks in Ctrl-Break thread dump. Manageable. (Introduced in 6.) The jstack -lcommand provides equivalent functionality.
-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.


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