测试堆空间常用jvm参数

古城微笑少年丶 2021-09-24 15:40 426阅读 0赞

1.查看所有参数的初始值，没有手动修改jvm参数的情况  -XX:+PrintFlagsInitial  
![20200905125841412.png][]

"D:\Program Files\Java\jdk1.8.0_181\bin\java.exe" -XX:+PrintFlagsInitial "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.6\lib\idea_rt.jar=59328:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.6\bin" -Dfile.encoding=UTF-8 -classpath "D:\Program Files\Java\jdk1.8.0_181\jre\lib\charsets.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\deploy.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\access-bridge-64.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\cldrdata.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\dnsns.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jaccess.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\jfxrt.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\localedata.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\nashorn.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunec.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunjce_provider.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunmscapi.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\sunpkcs11.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\ext\zipfs.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\javaws.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\jce.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\jfr.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\jfxswt.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\jsse.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\management-agent.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\plugin.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\resources.jar;D:\Program Files\Java\jdk1.8.0_181\jre\lib\rt.jar;E:\workplace5\test\target\classes" com.xqc.ExTest
    [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                               = true                                {C2 product}
         intx AllocateInstancePrefetchLines             = 1                                   {product}
         intx AllocatePrefetchDistance                  = -1                                  {product}
         intx AllocatePrefetchInstr                     = 0                                   {product}
         intx AllocatePrefetchLines                     = 3                                   {product}
         intx AllocatePrefetchStepSize                  = 16                                  {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                           = 2                                   {product}
         bool CICompilerCountPerCPU                     = false                               {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                   = 0                                   {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 CrashOnOutOfMemoryError                   = 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 EnableResourceManagementTLABCache         = 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 ExitOnOutOfMemoryError                    = false                               {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                           = 0                                   {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                           = 1000                                {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                        = 5                                   {product}
         intx MaxBCEAEstimateLevel                      = 5                                   {product}
         intx MaxBCEAEstimateSize                       = 150                                 {product}
        uintx MaxDirectMemorySize                       = 0                                   {product}
         bool MaxFDLimit                                = true                                {product}
        uintx MaxGCMinorPauseMillis                     = 4294967295                          {product}
        uintx MaxGCPauseMillis                          = 4294967295                          {product}
        uintx MaxHeapFreeRatio                          = 70                                  {manageable}
        uintx MaxHeapSize                               = 130862280                           {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                                = 15                                  {C2 product}
        uintx MaxMetaspaceExpansion                     = 5452592                             {product}
        uintx MaxMetaspaceFreeRatio                     = 70                                  {product}
        uintx MaxMetaspaceSize                          = 4294967295                          {product}
        uintx MaxNewSize                                = 4294967295                          {product}
         intx MaxNodeLimit                              = 80000                               {C2 product}
     uint64_t MaxRAM                                    = 0                                   {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                             = 21810376                            {pd product}
         bool MethodFlushing                            = true                                {product}
        uintx MinHeapDeltaBytes                         = 170392                              {product}
        uintx MinHeapFreeRatio                          = 40                                  {manageable}
         intx MinInliningThreshold                      = 250                                 {product}
         intx MinJumpTableSize                          = 10                                  {C2 pd product}
        uintx MinMetaspaceExpansion                     = 340784                              {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                                   = 1363144                             {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                                   = 5452592                             {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                         = 0                                   {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               = -1                                  {product}
         intx PrefetchFieldsAhead                       = -1                                  {product}
         intx PrefetchScanIntervalInBytes               = -1                                  {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                           = false                               {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                     = 50331648                            {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                         = 0                                   {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                          = 6                                   {pd product}
         bool StackTraceInThrowable                     = true                                {product}
         intx StackYellowPages                          = 3                                   {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                           = 0                                   {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                                    = false                               {product}
         bool UseAESIntrinsics                          = false                               {product}
         intx UseAVX                                    = 99                                  {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                             = false                               {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 UseCLMUL                                  = false                               {ARCH product}
         bool UseCMSBestFit                             = true                                {product}
         bool UseCMSCollectionPassing                   = true                                {product}
         bool UseCMSCompactAtFullCollection             = true                                {product}
         bool UseCMSInitiatingOccupancyOnly             = false                               {product}
         bool UseCRC32Intrinsics                        = false                               {product}
         bool UseCodeCacheFlushing                      = true                                {product}
         bool UseCompiler                               = true                                {product}
         bool UseCompilerSafepoints                     = true                                {product}
         bool UseCompressedClassPointers                = false                               {lp64_product}
         bool UseCompressedOops                         = false                               {lp64_product}
         bool UseConcMarkSweepGC                        = false                               {product}
         bool UseCondCardMark                           = false                               {C2 product}
         bool UseCountLeadingZerosInstruction           = false                               {ARCH product}
         bool UseCountTrailingZerosInstruction          = false                               {ARCH product}
         bool UseCountedLoopSafepoints                  = false                               {C2 product}
         bool UseCounterDecay                           = true                                {product}
         bool UseDivMod                                 = true                                {C2 product}
         bool UseDynamicNumberOfGCThreads               = false                               {product}
         bool UseFPUForSpilling                         = false                               {C2 product}
         bool UseFastAccessorMethods                    = true                                {product}
         bool UseFastEmptyMethods                       = true                                {product}
         bool UseFastJNIAccessors                       = true                                {product}
         bool UseFastStosb                              = false                               {ARCH product}
         bool UseG1GC                                   = false                               {product}
         bool UseGCLogFileRotation                      = false                               {product}
         bool UseGCOverheadLimit                        = true                                {product}
         bool UseGCTaskAffinity                         = false                               {product}
         bool UseHeavyMonitors                          = 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                                 = false                               {pd product}
         bool UseMontgomeryMultiplyIntrinsic            = false                               {C2 product}
         bool UseMontgomerySquareIntrinsic              = false                               {C2 product}
         bool UseMulAddIntrinsic                        = false                               {C2 product}
         bool UseMultiplyToLenIntrinsic                 = false                               {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 UseOptoBiasInlining                       = true                                {C2 product}
         bool UsePSAdaptiveSurvivorSizePolicy           = true                                {product}
         bool UseParNewGC                               = false                               {product}
         bool UseParallelGC                             = false                               {product}
         bool UseParallelOldGC                          = false                               {product}
         bool UsePerfData                               = true                                {product}
         bool UsePopCountInstruction                    = false                               {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}
         intx UseSSE                                    = 99                                  {product}
         bool UseSSE42Intrinsics                        = false                               {product}
         bool UseSerialGC                               = false                               {product}
         bool UseSharedSpaces                           = true                                {product}
         bool UseSignalChaining                         = true                                {product}
         bool UseSquareToLenIntrinsic                   = false                               {C2 product}
         bool UseStoreImmI16                            = true                                {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 UseUTCFileTimestamp                       = true                                {product}
         bool UseUnalignedLoadStores                    = false                               {ARCH product}
         bool UseVMInterruptibleIO                      = false                               {product}
         bool UseXMMForArrayCopy                        = false                               {product}
         bool UseXmmI2D                                 = false                               {ARCH product}
         bool UseXmmI2F                                 = false                               {ARCH product}
         bool UseXmmLoadAndClearUpper                   = true                                {ARCH product}
         bool UseXmmRegToRegMoveAll                     = false                               {ARCH product}
         bool VMThreadHintNoPreempt                     = false                               {product}
         intx VMThreadPriority                          = -1                                  {product}
         intx VMThreadStackSize                         = 0                                   {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}
    
    Process finished with exit code 0

2.查看所有参数的最终值，手动修改了jvm参数的情况  -XX:+PrintFlagsFinal  ，例如手动修改了堆的初始值和最大值  
![20200905130039617.png][]  
![20200905131011289.png][]  
![20200905131120364.png][]  
可以看到堆得初始大小和最大值已经是我们修改之后的了，50\*1024\*1024=52428800，不再是默认的**-Xms默认为物理内存的“1/64”，****-Xmx默认为物理内存的“1/4”**  
  
3.手动设置堆的初始值和最大值，-Xms50m -Xmx50m，上面的结果可以看到  
  
4.打印gc的详细过程-XX:+PrintGCDetails  
![20200905131624669.png][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70][]  
  
5.开启逃逸分析 -XX:+DoEscapeAnalysis,逃逸分析的好处是可以在栈上分配对象，而不是在堆上分配，提升速度、节省空间，方法已出栈，空间就释放了，jdk6u25版本之后的默认已开启了逃逸分析。**（也证明了堆不是分配对象的唯一空间）**

6.开启标量替换 -XX:+EliminateAllocations，对象通过逃逸分析之后，发现没有逃逸，可以将对象拆分成标量，Java虚拟机中的原始数据类型（int，long等数值类型以及reference类型等）都不能再进一步分解，它们就可以称为标量。这样就可以不用在堆中分配空间，速度也会提升，默认也是开启的。  
比如一个方法中使用了User对象，User对象里有id和name字段，这个对象实体没有逃逸的话，可以把聚合量拆解成两个局部变量，int id和String name,这样就不用在堆中分配了。  
  
7.开启同步省略（锁消除）-XX:+EliminateLocks：锁消除基于分析逃逸基础之上，开启锁消除必须开启逃逸分析，如果确定一个对象不会逃逸出线程，即对象被发现只能被一个线程访问到，无法被其它线程访问到，那该对象的读写就不会存在竞争，对这个变量的同步措施就可以消除掉。  
  
8.虚拟机为每一个线程预先在 Eden 区分配一块内存。JVM 在给线程中的对象分配内存时，首先在各个线程的TLAB 分配，当对象大于TLAB 中的剩余内存或 TLAB 的内存已用尽时，再采用上述的 CAS 进行内存分配。虚拟机是否启用TLAB，可以通过-XX:+/-UseTLAB参数来设定。  
![20200912145334896.png][]

[20200905125841412.png]: /images/20210923/8779538f7a3f43a6959f64a459ebcc82.png
[20200905130039617.png]: /images/20210923/2042e5be772142ee92ccf2d8a5ebb79e.png
[20200905131011289.png]: /images/20210923/6ba5955f3fd74eb49a98fe7813f6a6af.png
[20200905131120364.png]: /images/20210923/1b6db5f68e8c4a26b5f73dc4df7f0536.png
[20200905131624669.png]: /images/20210923/aeb90063ab054df880ed4c94c8924e12.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70]: /images/20210923/665de38b322d4491b0d632a5d2e3bf94.png
[20200912145334896.png]: /images/20210923/14f7b56203144873a77574f29a92e0cc.png