Java options-some useful-xx options

Document directory

• Categories of Java hotspot VM options
• Some useful-xx options

Http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp
Categories of Java hotspot VM options

 

Standard options recognized by the Java hotspot VM are described on the Java application launcher reference pages for Windows

, Solaris

And Linux

. This document deals exclusively with non-standard options recognized by the Java hotspot VM:

• Options that begin-X

  Are non-standard (not
  Guaranteed to be supported on All VM implementations), and are Subject
  To change without notice in subsequent releases of the JDK.

• Options that are specified-XX

  Are not stable and are not recommended for casual use. These options are subject to change without notice.

 

Some useful-xx options

 

Default values are listed for Java SE 6 for Solaris iSCSI with-server.
Some options may vary per architecture/OS/JVM version. Platforms with
Differing default value are listed in the description.

• Boolean options are turned on-XX:+<option>

  And turned off-XX:-<option>

  .

• Numeric options are set -XX:<option>=<number>

  .
  Numbers can include 'M' or 'M' for megabytes, 'K' or 'K' for kilobytes,
  And 'g' or 'G' for gigabytes (for example, 32 K is the same as 32768 ).

• String options are set-XX:<option>=<string>

  , Are usually used to specify a file, a path, or a list of commands

Flags markedManageable

Are dynamically writeable
Through the JDK Management Interface
(COM. Sun. Management. hotspotdiagnosticmxbean API) and also through
Jconsole. in monitoring and managing Java SE 6 platform applications

, Figure 3 shows an example. The manageable flags can also be set through jinfo-flag

.

The options below are loosely grouped into three categories.

• Behavioral options

  Change the basic behavior of the VM.

• Performance Tuning

  Options are knobs which can be used to tune VM performance.

• Debugging options

  Generally enable tracing, printing, or output of VM information.

 

Behavioral options

 

Option and default value	Description
-XX:-allowusersignalhandlers	Do not complain if the application instils 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 callto 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 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 Solaris only .)
-XX: + useboundthreads	Bind user level threads to kernel threads. (relevant 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 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 .)

Back to options

 

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 = 4 m	Sets the large page size used for the Java heap. (introduced in 1.4.0 update 1.) [amd64: 2 M.]
-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 iSCSI: 32 m; 1.3.1 x86: 2.5 m.]
-XX: maxpermsize = 64 m	Size of the permanent generation. [5.0 and newer: 64 bit VMS are scaled 30% larger; 1.4 amd64: 96 m; 1.3.1-Client: 32 M.]
-XX: minheapfreeratio = 40	Minimum Percentage of heap free after GC to avoid expansion.
-XX: newratio = 2	Ratio of new/old generation sizes. [iSCSI-Client: 8; x86-server: 8; x86-Client: 12.] -Client: 4 (1.3) 8 (1.3.1 +), x86: 12]
-XX: newsize = 2.125 m	Default size of New Generation (in bytes) [5.0 and newer: 64 bit VMS are scaled 30% larger; x86: 1 m; x86, 5.0 and older: 640 K]
-XX: reservedcodecachesize = 32 m	Reserved code cache size (in bytes)-maximum code cache size. [Solaris 64-bit, amd64, and-server x86: 48 m; In 1.5.0 _ 06 and earlier, Solaris 64-bit and and64: 1024 M.]
-XX: Required vorratio = 8	Ratio of Eden/mirror vor space size [Solaris amd64: 6; iSCSI in 1.3.1: 25; other Solaris platforms in 5.0 and earlier: 32]
-XX: target1_vorratio = 50	Desired percentage of specified vor space used after scavenge.
-XX: thread stacksize = 512	Thread stack size (in Kbytes). (0 means use default stack size) [ISCSI: 512; Solaris x86: 320 (was 256 prior in 5.0 and earlier ); 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/4 MB 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.

Back to options

 

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.
-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.