3、JVM运行时参数
3.0 相关问题
- JVM的参数，你知道的说一下 (百度)
- 说说你知道的几种主要的JVM参数（京东）
- JVM调优调的哪些参数？在哪里写这些参数？ （亚信）
- 内存调优参数都有什么？（顺丰）
- JVM调优调的哪些参数？问这样有什么好处？在哪里写这些参数（浪潮）
3.1 JVM参数选项类型
官网说明： docs.oracle.com/javase/8/do…
3.1.1 类型一：标准参数选项
3.1.1.1 特点
- 比较稳定，后续版本基本不会变化
- 以-开头
3.1.1.2 各种选项
选项包括:
-d32 使用 32 位数据模型 (如果可用)
-d64 使用 64 位数据模型 (如果可用)
-server 选择 "server" VM
默认 VM 是 server.
-cp <目录和 zip/jar 文件的类搜索路径>
-classpath <目录和 zip/jar 文件的类搜索路径>
用 ; 分隔的目录, JAR 档案
和 ZIP 档案列表, 用于搜索类文件。
-D<名称>=<值>
设置系统属性
-verbose:[class|gc|jni]
启用详细输出
-version 输出产品版本并退出
-version:<值>
警告: 此功能已过时, 将在
未来发行版中删除。
需要指定的版本才能运行
-showversion 输出产品版本并继续
-jre-restrict-search | -no-jre-restrict-search
警告: 此功能已过时, 将在
未来发行版中删除。
在版本搜索中包括/排除用户专用 JRE
-? -help 输出此帮助消息
-X 输出非标准选项的帮助
-ea[:<packagename>...|:<classname>]
-enableassertions[:<packagename>...|:<classname>]
按指定的粒度启用断言
-da[:<packagename>...|:<classname>]
-disableassertions[:<packagename>...|:<classname>]
禁用具有指定粒度的断言
-esa | -enablesystemassertions
启用系统断言
-dsa | -disablesystemassertions
禁用系统断言
-agentlib:<libname>[=<选项>]
加载本机代理库 <libname>, 例如 -agentlib:hprof
另请参阅 -agentlib:jdwp=help 和 -agentlib:hprof=help
-agentpath:<pathname>[=<选项>]
按完整路径名加载本机代理库
-javaagent:<jarpath>[=<选项>]
加载 Java 编程语言代理, 请参阅 java.lang.instrument
-splash:<imagepath>
使用指定的图像显示启动屏幕
有关详细信息, 请参阅 www.oracle.com/technetwork…。
运行java或者java -help可以看到所有的标准选项
3.1.1.3 补充内容：-server与-client
Hotspot JVM有两种模式，分别是server和client，分别通过-server和-client模式设置
- 在32位Windows系统上，默认使用Client类型的JVM。要想使用Server模式，则机器配置至少有2个以上的CPU和2G以上的物理内存。 client模式适用于对内存要求较小的桌面应用程序，默认使用Serial串行垃圾收集器
- 64位机器上只支持server模式的JVM，适用于需要大内存的应用程序，默认使用并行垃圾收集器
关于server和client的官网介绍为：docs.oracle.com/javase/8/do…
3.1.2 类型二：-X参数选项
3.1.2.1 特点
- 非标准化参数
- 功能还是比较稳定的。但官方说后续版本可能会变更
以-X开头
3.1.2.2 各种选项
-Xmixed 混合模式执行 (默认)
-Xint 仅解释模式执行
-Xcomp 仅采用即时编译器模式
-Xbootclasspath:<用 ; 分隔的目录和 zip/jar 文件>
设置搜索路径以引导类和资源
-Xbootclasspath/a:<用 ; 分隔的目录和 zip/jar 文件>
附加在引导类路径末尾
-Xbootclasspath/p:<用 ; 分隔的目录和 zip/jar 文件>
置于引导类路径之前
-Xdiag 显示附加诊断消息
-Xnoclassgc 禁用类垃圾收集
-Xincgc 启用增量垃圾收集
-Xloggc:<file> 将 GC 状态记录在文件中 (带时间戳)
-Xbatch 禁用后台编译
-Xms<size> 设置初始 Java 堆大小
-Xmx<size> 设置最大 Java 堆大小
-Xss<size> 设置 Java 线程堆栈大小
-Xprof 输出 cpu 配置文件数据
-Xfuture 启用最严格的检查, 预期将来的默认值
-Xrs 减少 Java/VM 对操作系统信号的使用 (请参阅文档)
-Xcheck:jni 对 JNI 函数执行其他检查
-Xshare:off 不尝试使用共享类数据
-Xshare:auto 在可能的情况下使用共享类数据 (默认)
-Xshare:on 要求使用共享类数据, 否则将失败。
-XshowSettings 显示所有设置并继续
-XshowSettings:all 显示所有设置并继续
-XshowSettings:vm 显示所有与 vm 相关的设置并继续
-XshowSettings:properties 显示所有属性设置并继续
-XshowSettings:locale 显示所有与区域设置相关的设置并继续
-X 选项是非标准选项, 如有更改, 恕不另行通知。
运行java -X命令可以看到所有的X选项
3.1.2.3 JVM的JIT编译模式相关的选项
3.1.2.1.1 -Xint
- 混合模式，默认模式，让JIT根据程序运行的情况，有选择地将某些代码编译成本地代码
3.1.2.1.2 -Xcomp
- 禁用JIT，所有字节码都被解释执行，这个模式的速度最慢的
3.1.2.1.3 -Xmixed
- 所有字节码第一次使用就都被编译成本地代码，然后再执行
3.1.2.4 特别地
-
-Xmx -Xms -Xss属于 XX 参数？
- -Xms 设置初始 Java 堆大小，等价于-XX:InitialHeapSize
- -Xmx 设置最大 Java 堆大小，等价于-XX:MaxHeapSize
- -Xss 设置 Java 线程堆栈大小，-XX:ThreadStackSize
3.1.3 类型三：-XX参数选项
3.1.3.1 特点
- 非标准化参数
- 使用的最多的参数类型
- 这类选项属于实验性，不稳定
以-XX开头
3.1.3.2 作用
用于开发和调试JVM
3.1.3.3 分类
3.1.3.3.1 Boolean类型格式
-
-XX:+ 表示启用 option 属性
-
-XX:- 表示禁用 option 属性
-
举例
- -XX:-UseParallelGC 不选择垃圾收集器为并行收集器
- -XX:+UseG1GC 表示启用G1收集器
- -XX:+UseAdaptiveSizePolicy 自动选择年轻代区大小和相应的Survivor区比例
-
说明：因为有的指令默认是开启的，所以可以使用-关闭
3.1.3.3.2 非Boolean类型格式（key-value类型）
3.1.3.3.2.1 子类型1：数值型格式-XX:=
number表示数值，number可以带上单位，比如：'m' 、'M' 表示兆， 'k' 、'K' 表示Kb， 'g' 、 'G' 表示 g（例如 32k跟32768是一样的效果）
例如： -XX:NewSize=1024m 表示设置新生代初始大小为1024兆 -XX:MaxGCPauseMillis=500 表示设置GC停顿时间：500毫秒 -XX:GCTimeRatio=19 表示设置吞吐量 -XX:NewRatio=2 表示新生代与老年代的比例
3.1.3.3.2.2 子类型2：非数值型格式-XX:=
例如： -XX:HeapDumpPath=/usr/local/heapdump.hprof 用来指定heap转存文件的存储路径。
3.1.3.4 特别地
-
-XX:+PrintFlagsFinal
- 输出所有参数的名称和默认值
- 默认不包括Diagnostic和Experimental的参数
- 可以配合-XX:+UnlockDiagnosticVMOptions和-XX:UnlockExperimentalVMOptions使用
-
各种参数默认值（参考）
[Global flags]
intx ActiveProcessorCount = -1 {product}
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 AggressiveHeap = false {product}
bool AggressiveOpts = false {product}
intx AliasLevel = 3 {C2 product}
bool AlignVector = true {C2 product}
intx AllocateInstancePrefetchLines = 1 {product}
intx AllocatePrefetchDistance = 256 {product}
intx AllocatePrefetchInstr = 3 {product}
intx AllocatePrefetchLines = 3 {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 := 12 {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 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 := 526385152 {product}
uintx InitialRAMFraction = 64 {product}
double InitialRAMPercentage = 1.562500 {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 LoadExecStackDllInVMThread = true {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 := 8417968128 {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 := 2805989376 {product}
intx MaxNodeLimit = 75000 {C2 product}
uint64_t MaxRAM = 137438953472 {pd product}
uintx MaxRAMFraction = 4 {product}
double MaxRAMPercentage = 25.000000 {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}
double MinRAMPercentage = 50.000000 {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 := 175112192 {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 := 351272960 {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 = 13 {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 PreferContainerQuotaForCPUCount = true {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 = 2 {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 = true {ARCH product}
bool UseBMI2Instructions = true {ARCH product}
bool UseBiasedLocking = true {product}
bool UseBimorphicInlining = true {C2 product}
bool UseBoundThreads = 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 UseContainerSupport = true {product}
bool UseCountLeadingZerosInstruction = true {ARCH product}
bool UseCountTrailingZerosInstruction = true {ARCH product}
bool UseCountedLoopSafepoints = false {C2 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 UseLinuxPosixThreadCPUClocks = true {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 = true {C2 product}
bool UseMontgomerySquareIntrinsic = true {C2 product}
bool UseMulAddIntrinsic = true {C2 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 UseSquareToLenIntrinsic = true {C2 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 UseTransparentHugePages = false {product}
bool UseTypeProfile = true {product}
bool UseTypeSpeculation = true {C2 product}
bool UseUnalignedLoadStores = false {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}
3.2 添加JVM参数选项
3.2.1 Eclipse
3.2.2 IDEA
3.2.3 运行jar包
java -Xms50m -Xmx50m -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -jar demo.jar
3.2.4 通过Tomcat运行war包
- Linux系统下可以在tomcat/bin/catalina.sh中添加类似如下配置： JAVA_OPTS="-Xms512M -Xmx1024M"
- Windows系统下在catalina.bat中添加类似如下配置： set "JAVA_OPTS=-Xms512M -Xmx1024M"
3.2.5 程序运行过程中
- 使用jinfo -flag = 设置非Boolean类型参数
- 使用 jinfo -flag [+|-] 设置Boolean类型参数
3.3 常用的JVM参数选项
3.3.1 打印设置的XX选项及值
3.3.1.1 -XX:+PrintCommandLineFlags
可以让在程序运行前打印出用户手动设置或者JVM自动设置的XX选项
3.3.1.2 -XX:+PrintFlagsInitial
表示打印出所有XX选项的默认值
3.3.1.3 -XX:+PrintFlagsFinal
表示打印出XX选项在运行程序时生效的值
3.3.1.4 -XX:+PrintVMOptions
打印JVM的参数
3.3.2 堆、栈、方法区等内存大小设置
3.3.2.1 栈
-
-Xss128k
- 设置每个线程的栈大小为128k
- 等价于 -XX:ThreadStackSize=128k
3.3.2.2 堆内存
3.3.2.2.1 -Xms3550m
等价于-XX:InitialHeapSize，设置JVM初始堆内存为3550M
3.3.2.2.2 -Xmx3550m
等价于-XX:MaxHeapSize，设置JVM最大堆内存为3550M
3.3.2.2.3 -Xmn2g
- 设置年轻代大小为2G
- 官方推荐配置为整个堆大小的3/8
3.3.2.2.4 -XX:NewSize=1024m
设置年轻代初始值为1024M
3.3.2.2.5 -XX:MaxNewSize=1024m
设置年轻代最大值为1024M
3.3.2.2.6 -XX:SurvivorRatio=8
设置年轻代中Eden区与一个Survivor区的比值，默认为8
3.3.2.2.7 -XX:+UseAdaptiveSizePolicy
自动选择各区大小比例
3.3.2.2.8 -XX:NewRatio=4
设置老年代与年轻代（包括1个Eden和2个Survivor区）的比值
3.3.2.2.9 -XX:PretenureSizeThreadshold=1024
- 设置让大于此阈值的对象直接分配在老年代，单位为字节
- 只对Serial、ParNew收集器有效
3.3.2.2.10 -XX:MaxTenuringThreshold=15
- 默认值为15
- 新生代每次MinorGC后，还存活的对象年龄+1，当对象的年龄大于设置的这个值时就进入老年代
3.3.2.2.11 -XX:+PrintTenuringDistribution
让JVM在每次MinorGC后打印出当前使用的Survivor中对象的年龄分布
3.3.2.2.12 -XX:TargetSurvivorRatio
表示MinorGC结束后Survivor区域中占用空间的期望比例
3.3.2.3 方法区
3.3.2.3.1 永久代
- -XX:PermSize=256m
设置永久代初始值为256M
-
-XX:MaxPermSize=256m
设置永久代最大值为256M
3.3.2.3.2 元空间
-
-XX:MetaspaceSize
初始空间大小
-
-XX:MaxMetaspaceSize
最大空间，默认没有限制
-
-XX:+UseCompressedOops
压缩对象指针
-
-XX:+UseCompressedClassPointers
压缩类指针
-
-XX:CompressedClassSpaceSize
设置Klass Metaspace的大小，默认1G
3.3.2.4 直接内存
-
-XX:MaxDirectMemorySize
指定DirectMemory容量，若未指定，则默认与Java堆最大值一样
3.3.3 OutofMemory相关的选项
3.3.3.1 -XX:+HeapDumpOnOutOfMemoryError
表示在内存出现OOM的时候，把Heap转存(Dump)到文件以便后续分析
3.3.3.2 -XX:+HeapDumpBeforeFullGC
表示在出现FullGC之前，生成Heap转储文件
3.3.3.3 -XX:HeapDumpPath=
指定heap转存文件的存储路径
3.3.3.4 -XX:OnOutOfMemoryError
对OnOutOfMemoryError的运维处理 以部署在linux系统/opt/Server目录下的Server.jar为例 1.在run.sh启动脚本中添加jvm参数：
-XX:OnOutOfMemoryError=/opt/Server/restart.sh
2.restart.sh脚本 linux环境：
!/bin/bash
pid=$(ps -ef|grep Server.jar|awk '{if($8=="java") {print $2}}')
kill -9 $pid
cd /opt/Server/;sh run.sh
Windows环境：
echo off
wmic process where Name='java.exe' delete
cd D:\Server
start run.bat
指定一个可行性程序或者脚本的路径，当发生OOM的时候，去执行这个脚本
3.3.4 垃圾收集器相关选项
-
7款经典收集器与垃圾分代之间的关系
-
垃圾收集器的组合关系
- 两个收集器间有连线，表明它们可以搭配使用： Serial/Serial Old、Serial/CMS、ParNew/Serial Old、ParNew/CMS、Parallel Scavenge/Serial Old、Parallel Scavenge/Parallel Old、G1；
- 其中Serial Old作为CMS出现"Concurrent Mode Failure"失败的后备预案。
- (红色虚线)由于维护和兼容性测试的成本，在JDK 8时将Serial+CMS、ParNew+Serial Old这两个组合声明为废弃（JEP 173），并在JDK 9中完全取消了这些组合的支持（JEP214），即：移除。
- (绿色虚线)JDK 14中：弃用Parallel Scavenge和SerialOld GC组合 （JEP 366）
- (青色虚线)JDK 14中：删除CMS垃圾回收器 （JEP 363）
3.3.5 GC日志相关选项
3.3.5.1 常用参数
-
-verbose:gc
- 输出gc日志信息，默认输出到标准输出
- 可以独立使用
-
-XX:+PrintGC
- 等同于-verbose:gc 表示打开简化的GC日志
- 可以独立使用
-
-XX:+PrintGCDetails
- 在发生垃圾回收时打印内存回收详细的日志， 并在进程退出时输出当前内存各区域分配情况
- 可以独立使用
-
-XX:+PrintGCTimeStamps
- 输出GC发生时的时间戳
- 不可以独立使用，需要配合-XX:+PrintGCDetails使用
-
-XX:+PrintGCDateStamps
- 输出GC发生时的时间戳（以日期的形式，如 2013-05-04T21:53:59.234+0800）
- 不可以独立使用，需要配合-XX:+PrintGCDetails使用
-
-XX:+PrintHeapAtGC
- 每一次GC前和GC后，都打印堆信息
- 可以独立使用
-
-Xloggc:
- 把GC日志写入到一个文件中去，而不是打印到标准输出中
3.3.5.2 其他参数
-
-XX:+TraceClassLoading
- 监控类的加载
-
-XX:+PrintGCApplicationStoppedTime
- 打印GC时线程的停顿时间
-
-XX:+PrintGCApplicationConcurrentTime
- 垃圾收集之前打印出应用未中断的执行时间
-
-XX:+PrintReferenceGC
- 记录回收了多少种不同引用类型的引用
-
-XX:+PrintTenuringDistribution
- 让JVM在每次MinorGC后打印出当前使用的Survivor中对象的年龄分布
-
-XX:+UseGCLogFileRotation
- 启用GC日志文件的自动转储
-
-XX:NumberOfGClogFiles=1
- GC日志文件的循环数目
-
-XX:GCLogFileSize=1M
- 控制GC日志文件的大小
3.3.6 其他参数
-
-XX:+DisableExplicitGC
- 禁止hotspot执行System.gc()，默认禁用
-
-XX:ReservedCodeCacheSize=[g|m|k]、-XX:InitialCodeCacheSize=[g|m|k]
- 指定代码缓存的大小
-
-XX:+UseCodeCacheFlushing
- 使用该参数让jvm放弃一些被编译的代码， 避免代码缓存被占满时JVM切换到interpreted-only的情况
-
-XX:+DoEscapeAnalysis
- 开启逃逸分析
-
-XX:+UseBiasedLocking
- 开启偏向锁
-
-XX:+UseLargePages
- 开启使用大页面
-
-XX:+UseTLAB
- 使用TLAB，默认打开
-
-XX:+PrintTLAB
- 打印TLAB的使用情况
-
-XX:TLABSize
- 设置TLAB大小
3.4 按功能性质区分JVM参数选项
Java HotSpot VM中-XX:的可配置参数列表进行描述；
这些参数可以被松散的聚合成三类：
- 行为参数（Behavioral Options）：用于改变jvm的一些基础行为；
- 性能调优（Performance Tuning）：用于jvm的性能调优；
- 调试参数（Debugging Options）：一般用于打开跟踪、打印、输出等jvm参数，用于显示jvm更加详细的信息；
行为参数(功能开关)
-XX:-DisableExplicitGC 禁止调用System.gc()；但jvm的gc仍然有效
-XX:+MaxFDLimit 最大化文件描述符的数量限制
-XX:+ScavengeBeforeFullGC 新生代GC优先于Full GC执行
-XX:+UseGCOverheadLimit 在抛出OOM之前限制jvm耗费在GC上的时间比例
-XX:-UseConcMarkSweepGC 对老生代采用并发标记交换算法进行GC
-XX:-UseParallelGC 启用并行GC
-XX:-UseParallelOldGC 对Full GC启用并行，当-XX:-UseParallelGC启用时该项自动启用
-XX:-UseSerialGC 启用串行GC
-XX:+UseThreadPriorities 启用本地线程优先级
``
性能调优
```java
-XX:LargePageSizeInBytes=4m 设置用于Java堆的大页面尺寸
-XX:MaxHeapFreeRatio=70 GC后java堆中空闲量占的最大比例
-XX:MaxNewSize=size 新生成对象能占用内存的最大值
-XX:MaxPermSize=64m 老生代对象能占用内存的最大值
-XX:MinHeapFreeRatio=40 GC后java堆中空闲量占的最小比例
-XX:NewRatio=2 新生代内存容量与老生代内存容量的比例
-XX:NewSize=2.125m 新生代对象生成时占用内存的默认值
-XX:ReservedCodeCacheSize=32m 保留代码占用的内存容量
-XX:ThreadStackSize=512 设置线程栈大小，若为0则使用系统默认值
-XX:+UseLargePages 使用大页面内存
调试参数
-XX:-CITime 打印消耗在JIT编译的时间
-XX:ErrorFile=./hs_err_pid<pid>.log 保存错误日志或者数据到文件中
-XX:-ExtendedDTraceProbes 开启solaris特有的dtrace探针
-XX:HeapDumpPath=./java_pid<pid>.hprof 指定导出堆信息时的路径或文件名
-XX:-HeapDumpOnOutOfMemoryError 当首次遭遇OOM时导出此时堆中相关信息
-XX:OnError="<cmd args>;<cmd args>" 出现致命ERROR之后运行自定义命令
-XX:OnOutOfMemoryError="<cmd args>;<cmd args>" 当首次遭遇OOM时执行自定义命令
-XX:-PrintClassHistogram 遇到Ctrl-Break后打印类实例的柱状信息，与jmap -histo功能相同
-XX:-PrintConcurrentLocks 遇到Ctrl-Break后打印并发锁的相关信息，与jstack -l功能相同
-XX:-PrintCommandLineFlags 打印在命令行中出现过的标记
-XX:-PrintCompilation 当一个方法被编译时打印相关信息
-XX:-PrintGC 每次GC时打印相关信息
-XX:-PrintGC Details 每次GC时打印详细信息
-XX:-PrintGCTimeStamps 打印每次GC的时间戳
-XX:-TraceClassLoading 跟踪类的加载信息
-XX:-TraceClassLoadingPreorder 跟踪被引用到的所有类的加载信息
-XX:-TraceClassResolution 跟踪常量池
-XX:-TraceClassUnloading 跟踪类的卸载信息
-XX:-TraceLoaderConstraints 跟踪类加载器约束的相关信息
3.5 通过Java代码获取JVM参数
Java提供了java.lang.management包用于监视和管理Java虚拟机和Java运行时中的其他组件，它允许本地和远程监控和管理运行的Java虚拟机。其中ManagementFactory这个类还是挺常用的。另外还有Runtime类也可以获取一些内存、CPU核数等相关的数据。
通过这些api可以监控我们的应用服务器的堆内存使用情况，设置一些阈值进行报警等处理。
/**
*
* 监控我们的应用服务器的堆内存使用情况，设置一些阈值进行报警等处理
*
* @author shkstart
* @create 15:23
*/
public class MemoryMonitor {
public static void main(String[] args) {
MemoryMXBean memorymbean = ManagementFactory.getMemoryMXBean();
MemoryUsage usage = memorymbean.getHeapMemoryUsage();
System.out.println("INIT HEAP: " + usage.getInit() / 1024 / 1024 + "m");
System.out.println("MAX HEAP: " + usage.getMax() / 1024 / 1024 + "m");
System.out.println("USE HEAP: " + usage.getUsed() / 1024 / 1024 + "m");
System.out.println("\nFull Information:");
System.out.println("Heap Memory Usage: " + memorymbean.getHeapMemoryUsage());
System.out.println("Non-Heap Memory Usage: " + memorymbean.getNonHeapMemoryUsage());
System.out.println("=======================通过java来获取相关系统状态============================ ");
System.out.println("当前堆内存大小totalMemory " + (int) Runtime.getRuntime().totalMemory() / 1024 / 1024 + "m");// 当前堆内存大小
System.out.println("空闲堆内存大小freeMemory " + (int) Runtime.getRuntime().freeMemory() / 1024 / 1024 + "m");// 空闲堆内存大小
System.out.println("最大可用总堆内存maxMemory " + Runtime.getRuntime().maxMemory() / 1024 / 1024 + "m");// 最大可用总堆内存大小
}
}
输出如下：
INIT HEAP: 100m
MAX HEAP: 96m
USE HEAP: 3m
Full Information:
Heap Memory Usage: init = 104857600(102400K) used = 3162256(3088K) committed = 100663296(98304K) max = 100663296(98304K)
Non-Heap Memory Usage: init = 2555904(2496K) used = 5207432(5085K) committed = 8060928(7872K) max = -1(-1K)
=======================通过java来获取相关系统状态========================
当前堆内存大小totalMemory 96m
空闲堆内存大小freeMemory 92m
最大可用总堆内存maxMemory 96m
3.5.1 通过Runtime获取
public class HeapSpaceInitial {
public static void main(String[] args) {
//返回Java虚拟机中的堆内存总量
long initialMemory = Runtime.getRuntime().totalMemory() / 1024 / 1024;
//返回Java虚拟机试图使用的最大堆内存量
long maxMemory = Runtime.getRuntime().maxMemory() / 1024 / 1024;
System.out.println("-Xms : " + initialMemory + "M");
System.out.println("-Xmx : " + maxMemory + "M");
System.out.println("系统内存大小为：" + maxMemory * 4.0 / 1024 + "G");
System.out.println("系统内存大小为：" + initialMemory * 64.0 / 1024 + "G");
}
}
