java -showversion -helpjava version "1.8.0_66"Java(TM) SE Runtime Environment (build 1.8.0_66-b17)Java HotSpot(TM) 64-Bit Server VM (build 25.66-b17, mixed mode)Usage: java [-options] class [args...] (to execute a class) or java [-options] -jar jarfile [args...] (to execute a jar file)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 <class search path of directories and zip/jar files> -classpath <class search path of directories and zip/jar files> A : separated list of directories, JAR archives, and ZIP archives to search for class files. -D<name>=<value> set a system property -verbose:[class|gc|jni] enable verbose output -version print product version and exit -version:<value> Warning: this feature is deprecated and will be removed in a future release. require the specified version to run -showversion print product version and continue -jre-restrict-search | -no-jre-restrict-search Warning: this feature is deprecated and will be removed in a future release. include/exclude user private JREs in the version search -? -help print this help message -X print help on non-standard options -ea[:<packagename>...|:<classname>] -enableassertions[:<packagename>...|:<classname>] enable assertions with specified granularity -da[:<packagename>...|:<classname>] -disableassertions[:<packagename>...|:<classname>] disable assertions with specified granularity -esa | -enablesystemassertions enable system assertions -dsa | -disablesystemassertions disable system assertions -agentlib:<libname>[=<options>] load native agent library <libname>, e.g. -agentlib:hprof see also, -agentlib:jdwp=help and -agentlib:hprof=help -agentpath:<pathname>[=<options>] load native agent library by full pathname -javaagent:<jarpath>[=<options>] load Java programming language agent, see java.lang.instrument -splash:<imagepath> show splash screen with specified imageSee http://www.oracle.com/technetwork/java/javase/documentation/index.html for more details. |
常用命令行部分选项说明
-cp、-classpath：目录和压缩的或.jar文件通过:（在 Windows 上通过;）来分隔。设置应用程序类和资源的搜索路径。如果不使用-classpath和-cp，也不设置CLASSPATH环境变量，那么缺省情况下，用户类路径是当前目录.。-help、-?：打印使用消息。-fullversion：印出 JVM 的构建和版本信息。-showversion：打印产品版本并继续。-verbose:<option>[,<option>...]：启用详细输出。使用逗号分隔多个选项。可用选项为：class：为装入的每个类的stderr写入一个条目。gc：提供详细的垃圾回收信息。jni：向stderr写入信息，描述应用程序和 JVM 所调用的JNI服务。
-version：印出 JVM 的完全构建和版本信息。
java -showversion -Xjava version "1.8.0_66"Java(TM) SE Runtime Environment (build 1.8.0_66-b17)Java HotSpot(TM) 64-Bit Server VM (build 25.66-b17, mixed mode) -Xmixed mixed mode execution (default) -Xint interpreted mode execution only -Xbootclasspath:<directories and zip/jar files separated by :> set search path for bootstrap classes and resources -Xbootclasspath/a:<directories and zip/jar files separated by :> append to end of bootstrap class path -Xbootclasspath/p:<directories and zip/jar files separated by :> prepend in front of bootstrap class path -Xdiag show additional diagnostic messages -Xnoclassgc disable class garbage collection -Xincgc enable incremental garbage collection -Xloggc:<file> log GC status to a file with time stamps -Xbatch disable background compilation -Xms<size> set initial Java heap size -Xmx<size> set maximum Java heap size -Xss<size> 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 continueThe -X options are non-standard and subject to change without notice.The following options are Mac OS X specific: -XstartOnFirstThread run the main() method on the first (AppKit) thread -Xdock:name=<application name>" override default application name displayed in dock -Xdock:icon=<path to icon file> override default icon displayed in dock |
java -XX:+PrintFlagsFinal -version |
输出如下 700 多个可设置参数及相应的值，表格的每一行包括五列，来表示一个XX参数。第一列表示参数的数据类型，第二列是名称，第四列为值，第五列是参数的类别。第三列=表示第四列是参数的默认值，而:=表明了参数被用户或者 JVM 赋值了。
可以设置的参数默认是不包括diagnostic或experimental系的。要在-XX:+PrintFlagsFinal的输出里看到这两种参数的信息，分别需要显式指定-XX:+UnlockDiagnosticVMOptions和-XX:+UnlockExperimentalVMOptions。
如果我们只想看下所有 XX 参数的默认值，可以使用-XX:+PrintFlagsInitial，只是展示了第三列为=的数据（也包括那些被设置其他值的参数），如果加上-XX:+UnlockDiagnosticVMOptions参数会有 800 多个。
[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 = false {product} intx AutoBoxCacheMax = 128 {C2 product} uintx AutoGCSelectPauseMillis = 5000 {product} intx BCEATraceLevel = 0 {product} intx BackEdgeThreshold = 100000 {pd product} bool BackgroundCompilation = true {pd product} uintx BaseFootPrintEstimate = 268435456 {product} intx BiasedLockingBulkRebiasThreshold = 20 {product} intx BiasedLockingBulkRevokeThreshold = 40 {product} intx BiasedLockingDecayTime = 25000 {product} intx BiasedLockingStartupDelay = 4000 {product} bool BindGCTaskThreadsToCPUs = false {product} bool BlockLayoutByFrequency = true {C2 product} intx BlockLayoutMinDiamondPercentage = 20 {C2 product} bool BlockLayoutRotateLoops = true {C2 product} bool BranchOnRegister = false {C2 product} bool BytecodeVerificationLocal = false {product} bool BytecodeVerificationRemote = true {product} bool C1OptimizeVirtualCallProfiling = true {C1 product} bool C1ProfileBranches = true {C1 product} bool C1ProfileCalls = true {C1 product} bool C1ProfileCheckcasts = true {C1 product} bool C1ProfileInlinedCalls = true {C1 product} bool C1ProfileVirtualCalls = true {C1 product} bool C1UpdateMethodData = true {C1 product} intx CICompilerCount := 3 {product} bool CICompilerCountPerCPU = true {product} bool CITime = false {product} bool CMSAbortSemantics = false {product} uintx CMSAbortablePrecleanMinWorkPerIteration = 100 {product} intx CMSAbortablePrecleanWaitMillis = 100 {manageable} uintx CMSBitMapYieldQuantum = 10485760 {product} uintx CMSBootstrapOccupancy = 50 {product} bool CMSClassUnloadingEnabled = true {product} uintx CMSClassUnloadingMaxInterval = 0 {product} bool CMSCleanOnEnter = true {product} bool CMSCompactWhenClearAllSoftRefs = true {product} uintx CMSConcMarkMultiple = 32 {product} bool CMSConcurrentMTEnabled = true {product} uintx CMSCoordinatorYieldSleepCount = 10 {product} bool CMSDumpAtPromotionFailure = false {product} bool CMSEdenChunksRecordAlways = true {product} uintx CMSExpAvgFactor = 50 {product} bool CMSExtrapolateSweep = false {product} uintx CMSFullGCsBeforeCompaction = 0 {product} uintx CMSIncrementalDutyCycle = 10 {product} uintx CMSIncrementalDutyCycleMin = 0 {product} bool CMSIncrementalMode = false {product} uintx CMSIncrementalOffset = 0 {product} bool CMSIncrementalPacing = true {product} uintx CMSIncrementalSafetyFactor = 10 {product} uintx CMSIndexedFreeListReplenish = 4 {product} intx CMSInitiatingOccupancyFraction = -1 {product} uintx CMSIsTooFullPercentage = 98 {product} double CMSLargeCoalSurplusPercent = 0.950000 {product} double CMSLargeSplitSurplusPercent = 1.000000 {product} bool CMSLoopWarn = false {product} uintx CMSMaxAbortablePrecleanLoops = 0 {product} intx CMSMaxAbortablePrecleanTime = 5000 {product} uintx CMSOldPLABMax = 1024 {product} uintx CMSOldPLABMin = 16 {product} uintx CMSOldPLABNumRefills = 4 {product} uintx CMSOldPLABReactivityFactor = 2 {product} bool CMSOldPLABResizeQuicker = false {product} uintx CMSOldPLABToleranceFactor = 4 {product} bool CMSPLABRecordAlways = true {product} uintx CMSParPromoteBlocksToClaim = 16 {product} bool CMSParallelInitialMarkEnabled = true {product} bool CMSParallelRemarkEnabled = true {product} bool CMSParallelSurvivorRemarkEnabled = true {product} uintx CMSPrecleanDenominator = 3 {product} uintx CMSPrecleanIter = 3 {product} uintx CMSPrecleanNumerator = 2 {product} bool CMSPrecleanRefLists1 = true {product} bool CMSPrecleanRefLists2 = false {product} bool CMSPrecleanSurvivors1 = false {product} bool CMSPrecleanSurvivors2 = true {product} uintx CMSPrecleanThreshold = 1000 {product} bool CMSPrecleaningEnabled = true {product} bool CMSPrintChunksInDump = false {product} bool CMSPrintEdenSurvivorChunks = false {product} bool CMSPrintObjectsInDump = false {product} uintx CMSRemarkVerifyVariant = 1 {product} bool CMSReplenishIntermediate = true {product} uintx CMSRescanMultiple = 32 {product} uintx CMSSamplingGrain = 16384 {product} bool CMSScavengeBeforeRemark = false {product} uintx CMSScheduleRemarkEdenPenetration = 50 {product} uintx CMSScheduleRemarkEdenSizeThreshold = 2097152 {product} uintx CMSScheduleRemarkSamplingRatio = 5 {product} double CMSSmallCoalSurplusPercent = 1.050000 {product} double CMSSmallSplitSurplusPercent = 1.100000 {product} bool CMSSplitIndexedFreeListBlocks = true {product} intx CMSTriggerInterval = -1 {manageable} uintx CMSTriggerRatio = 80 {product} intx CMSWaitDuration = 2000 {manageable} uintx CMSWorkQueueDrainThreshold = 10 {product} bool CMSYield = true {product} uintx CMSYieldSleepCount = 0 {product} uintx CMSYoungGenPerWorker = 67108864 {pd product} uintx CMS_FLSPadding = 1 {product} uintx CMS_FLSWeight = 75 {product} uintx CMS_SweepPadding = 1 {product} uintx CMS_SweepTimerThresholdMillis = 10 {product} uintx CMS_SweepWeight = 75 {product} bool CheckEndorsedAndExtDirs = false {product} bool CheckJNICalls = false {product} bool ClassUnloading = true {product} bool ClassUnloadingWithConcurrentMark = true {product} intx ClearFPUAtPark = 0 {product} bool ClipInlining = true {product} uintx CodeCacheExpansionSize = 65536 {pd product} uintx CodeCacheMinimumFreeSpace = 512000 {product} bool CollectGen0First = false {product} bool CompactFields = true {product} intx CompilationPolicyChoice = 3 {product}ccstrlist CompileCommand = {product} ccstr CompileCommandFile = {product}ccstrlist CompileOnly = {product} intx CompileThreshold = 10000 {pd product} bool CompilerThreadHintNoPreempt = true {product} intx CompilerThreadPriority = -1 {product} intx CompilerThreadStackSize = 0 {pd product} uintx CompressedClassSpaceSize = 1073741824 {product} uintx ConcGCThreads = 0 {product} intx ConditionalMoveLimit = 3 {C2 pd product} intx ContendedPaddingWidth = 128 {product} bool ConvertSleepToYield = true {pd product} bool ConvertYieldToSleep = false {product} bool CreateMinidumpOnCrash = false {product} bool CriticalJNINatives = true {product} bool DTraceAllocProbes = false {product} bool DTraceMethodProbes = false {product} bool DTraceMonitorProbes = false {product} bool Debugging = false {product} uintx DefaultMaxRAMFraction = 4 {product} intx DefaultThreadPriority = -1 {product} intx DeferPollingPageLoopCount = -1 {product} intx DeferThrSuspendLoopCount = 4000 {product} bool DeoptimizeRandom = false {product} bool DisableAttachMechanism = false {product} bool DisableExplicitGC = false {product} bool DisplayVMOutputToStderr = false {product} bool DisplayVMOutputToStdout = false {product} bool DoEscapeAnalysis = true {C2 product} bool DontCompileHugeMethods = true {product} bool DontYieldALot = false {pd product} ccstr DumpLoadedClassList = {product} bool DumpReplayDataOnError = true {product} bool DumpSharedSpaces = false {product} bool EagerXrunInit = false {product} intx EliminateAllocationArraySizeLimit = 64 {C2 product} bool EliminateAllocations = true {C2 product} bool EliminateAutoBox = true {C2 product} bool EliminateLocks = true {C2 product} bool EliminateNestedLocks = true {C2 product} intx EmitSync = 0 {product} bool EnableContended = true {product} bool EnableSharedLookupCache = true {product} bool EnableTracing = false {product} uintx ErgoHeapSizeLimit = 0 {product} ccstr ErrorFile = {product} ccstr ErrorReportServer = {product} double EscapeAnalysisTimeout = 20.000000 {C2 product} bool EstimateArgEscape = true {product} bool ExplicitGCInvokesConcurrent = false {product} bool ExplicitGCInvokesConcurrentAndUnloadsClasses = false {product} bool ExtendedDTraceProbes = false {product} ccstr ExtraSharedClassListFile = {product} bool FLSAlwaysCoalesceLarge = false {product} uintx FLSCoalescePolicy = 2 {product} double FLSLargestBlockCoalesceProximity = 0.990000 {product} bool FailOverToOldVerifier = true {product} bool FastTLABRefill = true {product} intx FenceInstruction = 0 {ARCH product} intx FieldsAllocationStyle = 1 {product} bool FilterSpuriousWakeups = true {product} ccstr FlightRecorderOptions = {product} bool ForceNUMA = false {product} bool ForceTimeHighResolution = false {product} intx FreqInlineSize = 325 {pd product} double G1ConcMarkStepDurationMillis = 10.000000 {product} uintx G1ConcRSHotCardLimit = 4 {product} uintx G1ConcRSLogCacheSize = 10 {product} intx G1ConcRefinementGreenZone = 0 {product} intx G1ConcRefinementRedZone = 0 {product} intx G1ConcRefinementServiceIntervalMillis = 300 {product} uintx G1ConcRefinementThreads = 0 {product} intx G1ConcRefinementThresholdStep = 0 {product} intx G1ConcRefinementYellowZone = 0 {product} uintx G1ConfidencePercent = 50 {product} uintx G1HeapRegionSize = 0 {product} uintx G1HeapWastePercent = 5 {product} uintx G1MixedGCCountTarget = 8 {product} intx G1RSetRegionEntries = 0 {product} uintx G1RSetScanBlockSize = 64 {product} intx G1RSetSparseRegionEntries = 0 {product} intx G1RSetUpdatingPauseTimePercent = 10 {product} intx G1RefProcDrainInterval = 10 {product} uintx G1ReservePercent = 10 {product} uintx G1SATBBufferEnqueueingThresholdPercent = 60 {product} intx G1SATBBufferSize = 1024 {product} intx G1UpdateBufferSize = 256 {product} bool G1UseAdaptiveConcRefinement = true {product} uintx GCDrainStackTargetSize = 64 {product} uintx GCHeapFreeLimit = 2 {product} uintx GCLockerEdenExpansionPercent = 5 {product} bool GCLockerInvokesConcurrent = false {product} uintx GCLogFileSize = 8192 {product} uintx GCPauseIntervalMillis = 0 {product} uintx GCTaskTimeStampEntries = 200 {product} uintx GCTimeLimit = 98 {product} uintx GCTimeRatio = 99 {product} uintx HeapBaseMinAddress = 2147483648 {pd product} bool HeapDumpAfterFullGC = false {manageable} bool HeapDumpBeforeFullGC = false {manageable} bool HeapDumpOnOutOfMemoryError = false {manageable} ccstr HeapDumpPath = {manageable} uintx HeapFirstMaximumCompactionCount = 3 {product} uintx HeapMaximumCompactionInterval = 20 {product} uintx HeapSizePerGCThread = 87241520 {product} bool IgnoreEmptyClassPaths = false {product} bool IgnoreUnrecognizedVMOptions = false {product} uintx IncreaseFirstTierCompileThresholdAt = 50 {product} bool IncrementalInline = true {C2 product} uintx InitialBootClassLoaderMetaspaceSize = 4194304 {product} uintx InitialCodeCacheSize = 2555904 {pd product} uintx InitialHeapSize := 134217728 {product} uintx InitialRAMFraction = 64 {product} uintx InitialSurvivorRatio = 8 {product} uintx InitialTenuringThreshold = 7 {product} uintx InitiatingHeapOccupancyPercent = 45 {product} bool Inline = true {product} ccstr InlineDataFile = {product} intx InlineSmallCode = 2000 {pd product} bool InlineSynchronizedMethods = true {C1 product} bool InsertMemBarAfterArraycopy = true {C2 product} intx InteriorEntryAlignment = 16 {C2 pd product} intx InterpreterProfilePercentage = 33 {product} bool JNIDetachReleasesMonitors = true {product} bool JavaMonitorsInStackTrace = true {product} intx JavaPriority10_To_OSPriority = -1 {product} intx JavaPriority1_To_OSPriority = -1 {product} intx JavaPriority2_To_OSPriority = -1 {product} intx JavaPriority3_To_OSPriority = -1 {product} intx JavaPriority4_To_OSPriority = -1 {product} intx JavaPriority5_To_OSPriority = -1 {product} intx JavaPriority6_To_OSPriority = -1 {product} intx JavaPriority7_To_OSPriority = -1 {product} intx JavaPriority8_To_OSPriority = -1 {product} intx JavaPriority9_To_OSPriority = -1 {product} bool LIRFillDelaySlots = false {C1 pd product} uintx LargePageHeapSizeThreshold = 134217728 {product} uintx LargePageSizeInBytes = 0 {product} bool LazyBootClassLoader = true {product} intx LiveNodeCountInliningCutoff = 40000 {C2 product} bool LogCommercialFeatures = false {product} intx LoopMaxUnroll = 16 {C2 product} intx LoopOptsCount = 43 {C2 product} intx LoopUnrollLimit = 60 {C2 pd product} intx LoopUnrollMin = 4 {C2 product} bool LoopUnswitching = true {C2 product} bool ManagementServer = false {product} uintx MarkStackSize = 4194304 {product} uintx MarkStackSizeMax = 536870912 {product} uintx MarkSweepAlwaysCompactCount = 4 {product} uintx MarkSweepDeadRatio = 1 {product} intx MaxBCEAEstimateLevel = 5 {product} intx MaxBCEAEstimateSize = 150 {product} uintx MaxDirectMemorySize = 0 {product} bool MaxFDLimit = true {product} uintx MaxGCMinorPauseMillis = 18446744073709551615 {product} uintx MaxGCPauseMillis = 18446744073709551615 {product} uintx MaxHeapFreeRatio = 100 {manageable} uintx MaxHeapSize := 2147483648 {product} intx MaxInlineLevel = 9 {product} intx MaxInlineSize = 35 {product} intx MaxJNILocalCapacity = 65536 {product} intx MaxJavaStackTraceDepth = 1024 {product} intx MaxJumpTableSize = 65000 {C2 product} intx MaxJumpTableSparseness = 5 {C2 product} intx MaxLabelRootDepth = 1100 {C2 product} intx MaxLoopPad = 11 {C2 product} uintx MaxMetaspaceExpansion = 5451776 {product} uintx MaxMetaspaceFreeRatio = 70 {product} uintx MaxMetaspaceSize = 18446744073709547520 {product} uintx MaxNewSize := 715653120 {product} intx MaxNodeLimit = 75000 {C2 product} uint64_t MaxRAM = 137438953472 {pd product} uintx MaxRAMFraction = 4 {product} intx MaxRecursiveInlineLevel = 1 {product} uintx MaxTenuringThreshold = 15 {product} intx MaxTrivialSize = 6 {product} intx MaxVectorSize = 32 {C2 product} uintx MetaspaceSize = 21807104 {pd product} bool MethodFlushing = true {product} uintx MinHeapDeltaBytes := 524288 {product} uintx MinHeapFreeRatio = 0 {manageable} intx MinInliningThreshold = 250 {product} intx MinJumpTableSize = 10 {C2 pd product} uintx MinMetaspaceExpansion = 339968 {product} uintx MinMetaspaceFreeRatio = 40 {product} uintx MinRAMFraction = 2 {product} uintx MinSurvivorRatio = 3 {product} uintx MinTLABSize = 2048 {product} intx MonitorBound = 0 {product} bool MonitorInUseLists = false {product} intx MultiArrayExpandLimit = 6 {C2 product} bool MustCallLoadClassInternal = false {product} uintx NUMAChunkResizeWeight = 20 {product} uintx NUMAInterleaveGranularity = 2097152 {product} uintx NUMAPageScanRate = 256 {product} uintx NUMASpaceResizeRate = 1073741824 {product} bool NUMAStats = false {product} ccstr NativeMemoryTracking = off {product} bool NeedsDeoptSuspend = false {pd product} bool NeverActAsServerClassMachine = false {pd product} bool NeverTenure = false {product} uintx NewRatio = 2 {product} uintx NewSize := 44564480 {product} uintx NewSizeThreadIncrease = 5320 {pd product} intx NmethodSweepActivity = 10 {product} intx NmethodSweepCheckInterval = 5 {product} intx NmethodSweepFraction = 16 {product} intx NodeLimitFudgeFactor = 2000 {C2 product} uintx NumberOfGCLogFiles = 0 {product} intx NumberOfLoopInstrToAlign = 4 {C2 product} intx ObjectAlignmentInBytes = 8 {lp64_product} uintx OldPLABSize = 1024 {product} uintx OldPLABWeight = 50 {product} uintx OldSize := 89653248 {product} bool OmitStackTraceInFastThrow = true {product}ccstrlist OnError = {product}ccstrlist OnOutOfMemoryError = {product} intx OnStackReplacePercentage = 140 {pd product} bool OptimizeFill = true {C2 product} bool OptimizePtrCompare = true {C2 product} bool OptimizeStringConcat = true {C2 product} bool OptoBundling = false {C2 pd product} intx OptoLoopAlignment = 16 {pd product} bool OptoScheduling = false {C2 pd product} uintx PLABWeight = 75 {product} bool PSChunkLargeArrays = true {product} intx ParGCArrayScanChunk = 50 {product} uintx ParGCDesiredObjsFromOverflowList = 20 {product} bool ParGCTrimOverflow = true {product} bool ParGCUseLocalOverflow = false {product} uintx ParallelGCBufferWastePct = 10 {product} uintx ParallelGCThreads = 4 {product} bool ParallelGCVerbose = false {product} uintx ParallelOldDeadWoodLimiterMean = 50 {product} uintx ParallelOldDeadWoodLimiterStdDev = 80 {product} bool ParallelRefProcBalancingEnabled = true {product} bool ParallelRefProcEnabled = false {product} bool PartialPeelAtUnsignedTests = true {C2 product} bool PartialPeelLoop = true {C2 product} intx PartialPeelNewPhiDelta = 0 {C2 product} uintx PausePadding = 1 {product} intx PerBytecodeRecompilationCutoff = 200 {product} intx PerBytecodeTrapLimit = 4 {product} intx PerMethodRecompilationCutoff = 400 {product} intx PerMethodTrapLimit = 100 {product} bool PerfAllowAtExitRegistration = false {product} bool PerfBypassFileSystemCheck = false {product} intx PerfDataMemorySize = 32768 {product} intx PerfDataSamplingInterval = 50 {product} ccstr PerfDataSaveFile = {product} bool PerfDataSaveToFile = false {product} bool PerfDisableSharedMem = false {product} intx PerfMaxStringConstLength = 1024 {product} intx PreInflateSpin = 10 {pd product} bool PreferInterpreterNativeStubs = false {pd product} intx PrefetchCopyIntervalInBytes = 576 {product} intx PrefetchFieldsAhead = 1 {product} intx PrefetchScanIntervalInBytes = 576 {product} bool PreserveAllAnnotations = false {product} bool PreserveFramePointer = false {pd product} uintx PretenureSizeThreshold = 0 {product} bool PrintAdaptiveSizePolicy = false {product} bool PrintCMSInitiationStatistics = false {product} intx PrintCMSStatistics = 0 {product} bool PrintClassHistogram = false {manageable} bool PrintClassHistogramAfterFullGC = false {manageable} bool PrintClassHistogramBeforeFullGC = false {manageable} bool PrintCodeCache = false {product} bool PrintCodeCacheOnCompilation = false {product} bool PrintCommandLineFlags = false {product} bool PrintCompilation = false {product} bool PrintConcurrentLocks = false {manageable} intx PrintFLSCensus = 0 {product} intx PrintFLSStatistics = 0 {product} bool PrintFlagsFinal := true {product} bool PrintFlagsInitial = false {product} bool PrintGC = false {manageable} bool PrintGCApplicationConcurrentTime = false {product} bool PrintGCApplicationStoppedTime = false {product} bool PrintGCCause = true {product} bool PrintGCDateStamps = false {manageable} bool PrintGCDetails = false {manageable} bool PrintGCID = false {manageable} bool PrintGCTaskTimeStamps = false {product} bool PrintGCTimeStamps = false {manageable} bool PrintHeapAtGC = false {product rw} bool PrintHeapAtGCExtended = false {product rw} bool PrintHeapAtSIGBREAK = true {product} bool PrintJNIGCStalls = false {product} bool PrintJNIResolving = false {product} bool PrintOldPLAB = false {product} bool PrintOopAddress = false {product} bool PrintPLAB = false {product} bool PrintParallelOldGCPhaseTimes = false {product} bool PrintPromotionFailure = false {product} bool PrintReferenceGC = false {product} bool PrintSafepointStatistics = false {product} intx PrintSafepointStatisticsCount = 300 {product} intx PrintSafepointStatisticsTimeout = -1 {product} bool PrintSharedArchiveAndExit = false {product} bool PrintSharedDictionary = false {product} bool PrintSharedSpaces = false {product} bool PrintStringDeduplicationStatistics = false {product} bool PrintStringTableStatistics = false {product} bool PrintTLAB = false {product} bool PrintTenuringDistribution = false {product} bool PrintTieredEvents = false {product} bool PrintVMOptions = false {product} bool PrintVMQWaitTime = false {product} bool PrintWarnings = true {product} uintx ProcessDistributionStride = 4 {product} bool ProfileInterpreter = true {pd product} bool ProfileIntervals = false {product} intx ProfileIntervalsTicks = 100 {product} intx ProfileMaturityPercentage = 20 {product} bool ProfileVM = false {product} bool ProfilerPrintByteCodeStatistics = false {product} bool ProfilerRecordPC = false {product} uintx PromotedPadding = 3 {product} uintx QueuedAllocationWarningCount = 0 {product} uintx RTMRetryCount = 5 {ARCH product} bool RangeCheckElimination = true {product} intx ReadPrefetchInstr = 0 {ARCH product} bool ReassociateInvariants = true {C2 product} bool ReduceBulkZeroing = true {C2 product} bool ReduceFieldZeroing = true {C2 product} bool ReduceInitialCardMarks = true {C2 product} bool ReduceSignalUsage = false {product} intx RefDiscoveryPolicy = 0 {product} bool ReflectionWrapResolutionErrors = true {product} bool RegisterFinalizersAtInit = true {product} bool RelaxAccessControlCheck = false {product} ccstr ReplayDataFile = {product} bool RequireSharedSpaces = false {product} uintx ReservedCodeCacheSize = 251658240 {pd product} bool ResizeOldPLAB = true {product} bool ResizePLAB = true {product} bool ResizeTLAB = true {pd product} bool RestoreMXCSROnJNICalls = false {product} bool RestrictContended = true {product} bool RewriteBytecodes = true {pd product} bool RewriteFrequentPairs = true {pd product} intx SafepointPollOffset = 256 {C1 pd product} intx SafepointSpinBeforeYield = 2000 {product} bool SafepointTimeout = false {product} intx SafepointTimeoutDelay = 10000 {product} bool ScavengeBeforeFullGC = true {product} intx SelfDestructTimer = 0 {product} uintx SharedBaseAddress = 34359738368 {product} ccstr SharedClassListFile = {product} uintx SharedMiscCodeSize = 122880 {product} uintx SharedMiscDataSize = 4194304 {product} uintx SharedReadOnlySize = 16777216 {product} uintx SharedReadWriteSize = 16777216 {product} bool ShowMessageBoxOnError = false {product} intx SoftRefLRUPolicyMSPerMB = 1000 {product} bool SpecialEncodeISOArray = true {C2 product} bool SplitIfBlocks = true {C2 product} intx StackRedPages = 1 {pd product} intx StackShadowPages = 20 {pd product} bool StackTraceInThrowable = true {product} intx StackYellowPages = 2 {pd product} bool StartAttachListener = false {product} intx StarvationMonitorInterval = 200 {product} bool StressLdcRewrite = false {product} uintx StringDeduplicationAgeThreshold = 3 {product} uintx StringTableSize = 60013 {product} bool SuppressFatalErrorMessage = false {product} uintx SurvivorPadding = 3 {product} uintx SurvivorRatio = 8 {product} intx SuspendRetryCount = 50 {product} intx SuspendRetryDelay = 5 {product} intx SyncFlags = 0 {product} ccstr SyncKnobs = {product} intx SyncVerbose = 0 {product} uintx TLABAllocationWeight = 35 {product} uintx TLABRefillWasteFraction = 64 {product} uintx TLABSize = 0 {product} bool TLABStats = true {product} uintx TLABWasteIncrement = 4 {product} uintx TLABWasteTargetPercent = 1 {product} uintx TargetPLABWastePct = 10 {product} uintx TargetSurvivorRatio = 50 {product} uintx TenuredGenerationSizeIncrement = 20 {product} uintx TenuredGenerationSizeSupplement = 80 {product} uintx TenuredGenerationSizeSupplementDecay = 2 {product} intx ThreadPriorityPolicy = 0 {product} bool ThreadPriorityVerbose = false {product} uintx ThreadSafetyMargin = 52428800 {product} intx ThreadStackSize = 1024 {pd product} uintx ThresholdTolerance = 10 {product} intx Tier0BackedgeNotifyFreqLog = 10 {product} intx Tier0InvokeNotifyFreqLog = 7 {product} intx Tier0ProfilingStartPercentage = 200 {product} intx Tier23InlineeNotifyFreqLog = 20 {product} intx Tier2BackEdgeThreshold = 0 {product} intx Tier2BackedgeNotifyFreqLog = 14 {product} intx Tier2CompileThreshold = 0 {product} intx Tier2InvokeNotifyFreqLog = 11 {product} intx Tier3BackEdgeThreshold = 60000 {product} intx Tier3BackedgeNotifyFreqLog = 13 {product} intx Tier3CompileThreshold = 2000 {product} intx Tier3DelayOff = 2 {product} intx Tier3DelayOn = 5 {product} intx Tier3InvocationThreshold = 200 {product} intx Tier3InvokeNotifyFreqLog = 10 {product} intx Tier3LoadFeedback = 5 {product} intx Tier3MinInvocationThreshold = 100 {product} intx Tier4BackEdgeThreshold = 40000 {product} intx Tier4CompileThreshold = 15000 {product} intx Tier4InvocationThreshold = 5000 {product} intx Tier4LoadFeedback = 3 {product} intx Tier4MinInvocationThreshold = 600 {product} bool TieredCompilation = true {pd product} intx TieredCompileTaskTimeout = 50 {product} intx TieredRateUpdateMaxTime = 25 {product} intx TieredRateUpdateMinTime = 1 {product} intx TieredStopAtLevel = 4 {product} bool TimeLinearScan = false {C1 product} bool TraceBiasedLocking = false {product} bool TraceClassLoading = false {product rw} bool TraceClassLoadingPreorder = false {product} bool TraceClassPaths = false {product} bool TraceClassResolution = false {product} bool TraceClassUnloading = false {product rw} bool TraceDynamicGCThreads = false {product} bool TraceGen0Time = false {product} bool TraceGen1Time = false {product} ccstr TraceJVMTI = {product} bool TraceLoaderConstraints = false {product rw} bool TraceMetadataHumongousAllocation = false {product} bool TraceMonitorInflation = false {product} bool TraceParallelOldGCTasks = false {product} intx TraceRedefineClasses = 0 {product} bool TraceSafepointCleanupTime = false {product} bool TraceSharedLookupCache = false {product} bool TraceSuspendWaitFailures = false {product} intx TrackedInitializationLimit = 50 {C2 product} bool TransmitErrorReport = false {product} bool TrapBasedNullChecks = false {pd product} bool TrapBasedRangeChecks = false {C2 pd product} intx TypeProfileArgsLimit = 2 {product} uintx TypeProfileLevel = 111 {pd product} intx TypeProfileMajorReceiverPercent = 90 {C2 product} intx TypeProfileParmsLimit = 2 {product} intx TypeProfileWidth = 2 {product} intx UnguardOnExecutionViolation = 0 {product} bool UnlinkSymbolsALot = false {product} bool Use486InstrsOnly = false {ARCH product} bool UseAES = true {product} bool UseAESIntrinsics = true {product} intx UseAVX = 1 {ARCH product} bool UseAdaptiveGCBoundary = false {product} bool UseAdaptiveGenerationSizePolicyAtMajorCollection = true {product} bool UseAdaptiveGenerationSizePolicyAtMinorCollection = true {product} bool UseAdaptiveNUMAChunkSizing = true {product} bool UseAdaptiveSizeDecayMajorGCCost = true {product} bool UseAdaptiveSizePolicy = true {product} bool UseAdaptiveSizePolicyFootprintGoal = true {product} bool UseAdaptiveSizePolicyWithSystemGC = false {product} bool UseAddressNop = true {ARCH product} bool UseAltSigs = false {product} bool UseAutoGCSelectPolicy = false {product} bool UseBMI1Instructions = false {ARCH product} bool UseBMI2Instructions = false {ARCH product} bool UseBiasedLocking = true {product} bool UseBimorphicInlining = true {C2 product} bool UseBoundThreads = true {product} bool UseBsdPosixThreadCPUClocks = true {product} bool UseCLMUL = true {ARCH product} bool UseCMSBestFit = true {product} bool UseCMSCollectionPassing = true {product} bool UseCMSCompactAtFullCollection = true {product} bool UseCMSInitiatingOccupancyOnly = false {product} bool UseCRC32Intrinsics = true {product} bool UseCodeCacheFlushing = true {product} bool UseCompiler = true {product} bool UseCompilerSafepoints = true {product} bool UseCompressedClassPointers := true {lp64_product} bool UseCompressedOops := true {lp64_product} bool UseConcMarkSweepGC = false {product} bool UseCondCardMark = false {C2 product} bool UseCountLeadingZerosInstruction = false {ARCH product} bool UseCountTrailingZerosInstruction = false {ARCH product} bool UseCounterDecay = true {product} bool UseDivMod = true {C2 product} bool UseDynamicNumberOfGCThreads = false {product} bool UseFPUForSpilling = true {C2 product} bool UseFastAccessorMethods = false {product} bool UseFastEmptyMethods = false {product} bool UseFastJNIAccessors = true {product} bool UseFastStosb = true {ARCH product} bool UseG1GC = false {product} bool UseGCLogFileRotation = false {product} bool UseGCOverheadLimit = true {product} bool UseGCTaskAffinity = false {product} bool UseHeavyMonitors = false {product} bool UseHugeTLBFS = false {product} bool UseInlineCaches = true {product} bool UseInterpreter = true {product} bool UseJumpTables = true {C2 product} bool UseLWPSynchronization = true {product} bool UseLargePages = false {pd product} bool UseLargePagesInMetaspace = false {product} bool UseLargePagesIndividualAllocation = false {pd product} bool UseLockedTracing = false {product} bool UseLoopCounter = true {product} bool UseLoopInvariantCodeMotion = true {C1 product} bool UseLoopPredicate = true {C2 product} bool UseMathExactIntrinsics = true {C2 product} bool UseMaximumCompactionOnSystemGC = true {product} bool UseMembar = true {pd product} bool UseMultiplyToLenIntrinsic = true {C2 product} bool UseNUMA = false {product} bool UseNUMAInterleaving = false {product} bool UseNewLongLShift = false {ARCH product} bool UseOSErrorReporting = false {pd product} bool UseOldInlining = true {C2 product} bool UseOnStackReplacement = true {pd product} bool UseOnlyInlinedBimorphic = true {C2 product} bool UseOprofile = false {product} bool UseOptoBiasInlining = true {C2 product} bool UsePSAdaptiveSurvivorSizePolicy = true {product} bool UseParNewGC = false {product} bool UseParallelGC := true {product} bool UseParallelOldGC = true {product} bool UsePerfData = true {product} bool UsePopCountInstruction = true {product} bool UseRDPCForConstantTableBase = false {C2 product} bool UseRTMDeopt = false {ARCH product} bool UseRTMLocking = false {ARCH product} bool UseSHA = false {product} bool UseSHA1Intrinsics = false {product} bool UseSHA256Intrinsics = false {product} bool UseSHA512Intrinsics = false {product} bool UseSHM = false {product} intx UseSSE = 4 {product} bool UseSSE42Intrinsics = true {product} bool UseSerialGC = false {product} bool UseSharedSpaces = false {product} bool UseSignalChaining = true {product} bool UseStoreImmI16 = false {ARCH product} bool UseStringDeduplication = false {product} bool UseSuperWord = true {C2 product} bool UseTLAB = true {pd product} bool UseThreadPriorities = true {pd product} bool UseTypeProfile = true {product} bool UseTypeSpeculation = true {C2 product} bool UseUnalignedLoadStores = true {ARCH product} bool UseVMInterruptibleIO = false {product} bool UseXMMForArrayCopy = true {product} bool UseXmmI2D = false {ARCH product} bool UseXmmI2F = false {ARCH product} bool UseXmmLoadAndClearUpper = true {ARCH product} bool UseXmmRegToRegMoveAll = true {ARCH product} bool VMThreadHintNoPreempt = false {product} intx VMThreadPriority = -1 {product} intx VMThreadStackSize = 1024 {pd product} intx ValueMapInitialSize = 11 {C1 product} intx ValueMapMaxLoopSize = 8 {C1 product} intx ValueSearchLimit = 1000 {C2 product} bool VerifyMergedCPBytecodes = true {product} bool VerifySharedSpaces = false {product} intx WorkAroundNPTLTimedWaitHang = 1 {product} uintx YoungGenerationSizeIncrement = 20 {product} uintx YoungGenerationSizeSupplement = 80 {product} uintx YoungGenerationSizeSupplementDecay = 8 {product} uintx YoungPLABSize = 4096 {product} bool ZeroTLAB = false {product} intx hashCode = 5 {product}java version "1.8.0_66"Java(TM) SE Runtime Environment (build 1.8.0_66-b17)Java HotSpot(TM) 64-Bit Server VM (build 25.66-b17, mixed mode) |
-XX:+PrintCommandLineFlags这个参数让 JVM 打印出那些已经被用户或者 JVM 设置过的详细的XX参数的名称和值。
它列举出-XX:+PrintFlagsFinal的结果中第三列有:=的参数。以这种方式，我们可以用-XX:+PrintCommandLineFlags作为快捷方式来查看修改过的参数。
java -XX:+PrintCommandLineFlags -version-XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2147483648 -XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseParallelGCjava version "1.8.0_66"Java(TM) SE Runtime Environment (build 1.8.0_66-b17)Java HotSpot(TM) 64-Bit Server VM (build 25.66-b17, mixed mode) |
输出如上，JVM 堆的初始值为系统内存的1/64，最大值为系统内存的1/4：
JDK11 默认使用 G1 垃圾回收算法
/usr/lib/jvm/jdk-11.0.1/bin/java -XX:+PrintCommandLineFlags -version-XX:G1ConcRefinementThreads=4 -XX:GCDrainStackTargetSize=64 -XX:InitialHeapSize=261987008 -XX:MaxHeapSize=4191792128 -XX:+PrintCommandLineFlags -XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GCjava version "11.0.1" 2018-10-16 LTSJava(TM) SE Runtime Environment 18.9 (build 11.0.1+13-LTS)Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.1+13-LTS, mixed mode) |
Java 垃圾回收器常用的命令行选项
对于采用<size>参数的选项，在数字后面加上k或K来表示千字节，加上m或M来表示兆字节，或者加上g或G来表示千兆字节。对于采用<percentage>参数的选项，使用从0到1的数字，例如，50%即0.5。
-Xmn：将新区域的初始和最大大小设置为指定的值。-Xmns：将新区域的初始大小设置为指定的值。-Xmnx：将新区域的最大大小设置为指定的值。-Xms：设置初始 Java 堆大小。-Xmx：设置应用程序的最大内存大小(-Xmx >= -Xms)。