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
Do not complain if the application installs signal handlers. (Relevant to Solaris and Linux only.)
Alternate signal stack size (in Kbytes). (Relevant to Solaris only, removed from 5.0.)
Disable calls to System.gc(), JVM still performs garbage collection when necessary.
Fail over to old verifier when the new type checker fails. (Introduced in 6.)
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.]
Bump the number of file descriptors to max. (Relevant  to Solaris only.)
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.)
Relax the access control checks in the verifier. (Introduced in 6.)
Do young generation GC prior to a full GC. (Introduced in 1.4.1.)
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.)
Bind user level threads to kernel threads. (Relevant to Solaris only.)
Use concurrent mark-sweep collection for the old generation. (Introduced in 1.4.1)
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.)
Use LWP-based instead of thread based synchronization. (Introduced in 1.4.0. Relevant to Solaris only.)
Use parallel garbage collection for scavenges. (Introduced in 1.4.1)
Use parallel garbage collection for the full collections. Enabling this option automatically sets -XX:+UseParallelGC. (Introduced in 5.0 update 6.)
Use serial garbage collection. (Introduced in 5.0.)
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]
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]
Use the new type checker with StackMapTable attributes. (Introduced in 5.0.)[5.0: false]
Use native thread priorities.
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
Turn on point performance compiler optimizations that are expected to be default in upcoming releases. (Introduced in 5.0 update 6.)
Number of method invocations/branches before compiling [-client: 1,500]
Sets the large page size used for the Java heap. (Introduced in 1.4.0 update 1.) [amd64: 2m.]
Maximum percentage of heap free after GC to avoid shrinking.
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.]
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.]
Minimum percentage of heap free after GC to avoid expansion.
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]
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]
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.]
Ratio of eden/survivor space size [Solaris amd64: 6; Sparc in 1.3.1: 25; other Solaris platforms in 5.0 and earlier: 32]
Desired percentage of survivor space used after scavenge.
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.]
Enable biased locking. For more details, see thistuning example. (Introduced in 5.0 update 6.) [5.0: false]
Use optimized versions of Get<Primitive>Field.
Use Intimate Shared Memory. [Not accepted for non-Solaris platforms.] For details, see Intimate Shared Memory.
Use large page memory. (Introduced in 5.0 update 5.) For details, see Java Support for Large Memory Pages.
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]
Enables caching of commonly allocated strings.
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.
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
Prints time spent in JIT Compiler. (Introduced in 1.4.0.)
If an error occurs, save the error data to this file. (Introduced in 6.)
Enable performance-impacting dtrace probes. (Introduced in 6. Relevant to Solaris only.)
Path to directory or filename for heap dump.Manageable. (Introduced in 1.4.2 update 12, 5.0 update 7.)
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)
Print a histogram of class instances on Ctrl-Break.Manageable. (Introduced in 1.4.2.) The jmap -histocommand provides equivalent functionality.
Print java.util.concurrent locks in Ctrl-Break thread dump. Manageable. (Introduced in 6.) The jstack -lcommand provides equivalent functionality.
Print flags that appeared on the command line. (Introduced in 5.0.)
Print message when a method is compiled.
Print messages at garbage collection. Manageable.
Print more details at garbage collection. Manageable. (Introduced in 1.4.0.)
Print timestamps at garbage collection. Manageable(Introduced in 1.4.0.)
Print tenuring age information.
Trace loading of classes.
Trace all classes loaded in order referenced (not loaded). (Introduced in 1.4.2.)
Trace constant pool resolutions. (Introduced in 1.4.2.)
Trace unloading of classes.
Trace recording of loader constraints. (Introduced in 6.)
Saves jvmstat binary data on exit.

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