Debugs of Sun JDK


JVM Debug Options for Sun JDK.


Debugging Option 


  • -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.
  • -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. 


Performance Option



  • -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 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:+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.


Behavioral Option




  • -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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