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如何查看jvm中的各种参数以及默认值

java water 196℃ 0评论

1 标准参数
标准参数(-),所有的JVM实现都必须实现这些参数的功能,而且向后兼容;
通过命令 java即可查看
如下

where options include:
-d32 use a 32-bit data model if available
-d64 use a 64-bit data model if available
-server to select the "server" VM
The default VM is server,
because you are running on a server-class machine.

-cp 
-classpath 
              A : separated list of directories, JAR archives,
              and ZIP archives to search for class files.
-D=
              set a system property
-verbose:[class|gc|jni]
              enable verbose output
-version      print product version and exit

2 非标准参数(-X)
非标准参数(-X),默认jvm实现这些参数的功能,但是并不保证所有jvm实现都满足,且不保证向后兼容;
通过命令 java -X,如下

-Xmixed           mixed mode execution (default)
-Xint             interpreted mode execution only
-Xbootclasspath:
                  set search path for bootstrap classes and resources
-Xbootclasspath/a:
                  append to end of bootstrap class path
-Xbootclasspath/p:
                  prepend in front of bootstrap class path
-Xdiag            show additional diagnostic messages
-Xnoclassgc       disable class garbage collection
-Xincgc           enable incremental garbage collection
-Xloggc:    log GC status to a file with time stamps
-Xbatch           disable background compilation
-Xms        set initial Java heap size
-Xmx        set maximum Java heap size
-Xss        set java thread stack size
-Xprof            output cpu profiling data
-Xfuture          enable strictest checks, anticipating future default
-Xrs              reduce use of OS signals by Java/VM (see documentation)
-Xcheck:jni       perform additional checks for JNI functions
-Xshare:off       do not attempt to use shared class data
-Xshare:auto      use shared class data if possible (default)
-Xshare:on        require using shared class data, otherwise fail.
-XshowSettings    show all settings and continue
-XshowSettings:all
                  show all settings and continue
-XshowSettings:vm show all vm related settings and continue
-XshowSettings:properties
                  show all property settings and continue
-XshowSettings:locale
                  show all locale related settings and continue

3 非Stable参数(-XX)
非Stable参数(-XX),此类参数各个jvm实现会有所不同,将来可能会随时取消,需要慎重使用(但是,这些参数往往是非常有用的). 通过命令java -XX:+PrintFlagsFinal

[Global flags]
uintx AdaptiveSizeDecrementScaleFactor = 4 {product}
uintx AdaptiveSizeMajorGCDecayTimeScale = 10 {product}
uintx AdaptiveSizePausePolicy = 0 {product}
uintx AdaptiveSizePolicyCollectionCostMargin = 50 {product}
uintx AdaptiveSizePolicyInitializingSteps = 20 {product}
uintx AdaptiveSizePolicyOutputInterval = 0 {product}
uintx AdaptiveSizePolicyWeight = 10 {product}
uintx AdaptiveSizeThroughPutPolicy = 0 {product}
uintx AdaptiveTimeWeight = 25 {product}
bool AdjustConcurrency = false {product}
bool AggressiveOpts = false {product}
intx AliasLevel = 3 {C2 product}
bool AlignVector = false {C2 product}
intx AllocateInstancePrefetchLines = 1 {product}
intx AllocatePrefetchDistance = 192 {product}
intx AllocatePrefetchInstr = 0 {product}
intx AllocatePrefetchLines = 4 {product}
intx AllocatePrefetchStepSize = 64 {product}
intx AllocatePrefetchStyle = 1 {product}
bool AllowJNIEnvProxy = false {product}
bool AllowNonVirtualCalls = false {product}
bool AllowParallelDefineClass = false {product}
bool AllowUserSignalHandlers = false {product}
bool AlwaysActAsServerClassMachine = false {product}
bool AlwaysCompileLoopMethods = false {product}
bool AlwaysLockClassLoader = false {product}
bool AlwaysPreTouch = false {product}
bool AlwaysRestoreFPU = false {product}
bool AlwaysTenure = false {product}
bool AssertOnSuspendWaitFailure = false {product}
bool AssumeMP = true {product}
intx AutoBoxCacheMax = 128 {C2 product}
uintx AutoGCSelectPauseMillis = 5000 {product}
intx BCEATraceLevel = 0 {product}
intx BackEdgeThreshold = 100000 {pd product}

也可以通过-XX:+PrintCommandLineFlags 。这个参数的作用是显示出VM初始化完毕后所有跟最初的默认值不同的参数及它们的值。
这个参数至少在Sun JDK 5上已经开始支持,Oracle/Sun JDK 6以及Oracle JDK 7上也可以使用。

再下来,-XX:+PrintFlagsInitial 。这个参数显示在处理参数之前所有可设置的参数及它们的值,然后直接退出程序。

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