# Java OpenJDK 8 This page describes the Optimization Pack for Java OpenJDK 8 JVM. ## Metrics ### Memory | Metric | Unit | Description | | ------------------------------- | ------- | ------------------------------------------------------------------------ | | mem\_used | bytes | The total amount of memory used | | jvm\_heap\_size | bytes | The size of the JVM heap memory | | jvm\_heap\_used | bytes | The amount of heap memory used | | jvm\_heap\_util | percent | The utilization % of heap memory | | jvm\_off\_heap\_used | bytes | The amount of non-heap memory used | | jvm\_heap\_old\_gen\_used | bytes | The amount of heap memory used (old generation) | | jvm\_heap\_young\_gen\_used | bytes | The amount of heap memory used (young generation) | | jvm\_heap\_old\_gen\_size | bytes | The size of the JVM heap memory (old generation) | | jvm\_heap\_young\_gen\_size | bytes | The size of the JVM heap memory (young generation) | | jvm\_memory\_used | bytes | The total amount of memory used across all the JVM memory pools | | jvm\_heap\_committed | bytes | The size of the JVM committed memory | | jvm\_memory\_buffer\_pool\_used | bytes | The total amount bytes used by buffers within the JVM buffer memory pool | ### CPU | Metric | Unit | Description | | --------- | ------- | --------------------------------------------------------------------------------------------------------------- | | cpu\_util | percent | The average CPU utilization % across all the CPUs (i.e., how much time on average the CPUs are busy doing work) | | cpu\_used | CPUs | The total amount of CPUs used | ### Garbage Collection | Metric | Unit | Description | | ----------------- | ------------- | ----------------------------------------------------------------------------------------- | | jvm\_gc\_time | percent | The % of wall clock time the JVM spent doing stop the world garbage collection activities | | jvm\_gc\_count | collections/s | The total number of stop the world JVM garbage collections that have occurred per second | | jvm\_gc\_duration | seconds | The average duration of a stop the world JVM garbage collection | ### Other metrics | Metric | Unit | Description | | ------------------------ | ------------ | --------------------------------------------------------------- | | jvm\_threads\_current | threads | The total number of active threads within the JVM | | jvm\_threads\_deadlocked | threads | The total number of deadlocked threads within the JVM | | jvm\_compilation\_time | milliseconds | The total time spent by the JVM JIT compiler compiling bytecode | ## Parameters ### Memory | Name | Type | Unit | Dafault | Domain | Restart | Description | | ----------------------------- | ----------- | --------- | ----------------------------------------- | ------------------------------------------------------ | ------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- | | jvm\_minHeapSize | integer | megabytes | You should select your own default value. | You should select your own domain. | yes | The minimum heap size. | | jvm\_maxHeapSize | integer | megabytes | You should select your own default value. | You should select your own domain. | yes | The maximum heap size. | | jvm\_maxRAM | integer | megabytes | You should select your own default value. | You should select your own domain. | yes | The maximum amount of memory used by the JVM. | | jvm\_initialRAMPercentage | real | percent | `1.563` | `0.1` → `100` | yes | The initial percentage of memory used by the JVM. | | jvm\_maxRAMPercentage | real | percent | `25.0` | `0.1` → `100.0` | yes | The percentage of memory used for maximum heap size, on systems with large physical memory size (more than 512MB). Requires Java 10, Java 8 Update 191 or later. | | jvm\_alwaysPreTouch | categorical | | `-AlwaysPreTouch` | `+AlwaysPreTouch`, `-AlwaysPreTouch` | yes | Pretouch pages during initialization. | | jvm\_metaspaceSize | integer | megabytes | `20` | You should select your own domain within 1 and 1024 | yes | The initial size of the allocated class metadata space. | | jvm\_maxMetaspaceSize | integer | megabytes | `20` | You should select your own domain within 1 and 1024 | yes | The maximum size of the allocated class metadata space. | | jvm\_useTransparentHugePages | categorical | | `-UseTransparentHugePages` | `+UseTransparentHugePages`, `-UseTransparentHugePages` | yes | Enables the use of large pages that can dynamically grow or shrink. | | jvm\_allocatePrefetchInstr | integer | | `0` | `0` → `3` | yes | Prefetch ahead of the allocation pointer. | | jvm\_allocatePrefetchDistance | integer | bytes | `0` | `0` → `512` | yes | Distance to prefetch ahead of allocation pointer. -1 use system-specific value (automatically determined). | | jvm\_allocatePrefetchLines | integer | lines | `3` | `1` → `64` | yes | The number of lines to prefetch ahead of array allocation pointer. | | jvm\_allocatePrefetchStyle | integer | | `1` | `0` → `3` | yes | Selects the prefetch instruction to generate. | | jvm\_useLargePages | categorical | | `+UseLargePages` | `+UseLargePages`, `-UseLargePages` | yes | Enable the use of large page memory. | ### Garbage Collection | Name | Type | Unit | Default | Domain | Restart | Description | | ------------------------------------- | ----------- | ------------ | ----------------------------------------- | ------------------------------------------------------------------ | ------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | jvm\_newRatio | integer | | `2` | `0` → `2147483647` | yes | The ratio of old/new generation sizes. | | jvm\_newSize | integer | megabytes | You should select your own default value. | You should select your own domain. | yes | Sets the initial and maximum size of the heap for the young generation (nursery). | | jvm\_maxNewSize | integer | megabytes | You should select your own default value. | You should select your own domain. | yes | Specifies the upper bound for the young generation size. | | jvm\_survivorRatio | integer | | `8` | `1` → `100` | yes | The ratio between the Eden and each Survivor-space within the JVM. For example, a jvm\_survivorRatio would mean that the Eden-space is 6 times one Survivor-space. | | jvm\_useAdaptiveSizePolicy | categorical | | `+UseAdaptiveSizePolicy` | `+UseAdaptiveSizePolicy`, `-UseAdaptiveSizePolicy` | yes | Enable adaptive generation sizing. Disable coupled with jvm\_targetSurvivorRatio. | | jvm\_adaptiveSizePolicyWeight | integer | | `10` | `0` → `100` | yes | The weighting given to the current Garbage Collection time versus previous GC times when checking the timing goal. | | jvm\_targetSurvivorRatio | integer | | `50` | `1` → `100` | yes | The desired percentage of Survivor-space used after young garbage collection. | | jvm\_minHeapFreeRatio | integer | | `40` | `1` → `99` | yes | The minimum percentage of heap free after garbage collection to avoid shrinking. | | jvm\_maxHeapFreeRatio | integer | | `70` | `0` → `100` | yes | The maximum percentage of heap free after garbage collection to avoid shrinking. | | jvm\_maxTenuringThreshold | integer | | `15` | `0` → `15` | yes | The maximum value for the tenuring threshold. | | jvm\_gcType | categorical | | `Parallel` | `Serial`, `Parallel`, `ConcMarkSweep`, `G1`, `ParNew` | yes | Type of the garbage collection algorithm. | | jvm\_concurrentGCThreads | integer | threads | You should select your own default value. | You should select your own domain. | yes | The number of threads concurrent garbage collection will use. | | jvm\_parallelGCThreads | integer | threads | You should select your own default value. | You should select your own domain. | yes | The number of threads garbage collection will use for parallel phases. | | jvm\_maxGCPauseMillis | integer | milliseconds | `200` | `1` → `1000` | yes | Adaptive size policy maximum GC pause time goal in millisecond. | | jvm\_resizePLAB | categorical | | `+ResizePLAB` | `+ResizePLAB`, `-ResizePLAB` | yes | Enables the dynamic resizing of promotion LABs. | | jvm\_GCTimeRatio | integer | | `99` | `0` → `100` | yes | The target fraction of time that can be spent in garbage collection before increasing the heap, computet as 1 / (1 + GCTimeRatio). | | jvm\_initiatingHeapOccupancyPercent | integer | | `45` | `0` → `100` | yes | Sets the percentage of the heap occupancy at which to start a concurrent GC cycle. | | jvm\_youngGenerationSizeIncrement | integer | | `20` | `0` → `100` | yes | The increment size for Young Generation adaptive resizing. | | jvm\_tenuredGenerationSizeIncrement | integer | | `20` | `0` → `100` | yes | The increment size for Old/Tenured Generation adaptive resizing. | | jvm\_adaptiveSizeDecrementScaleFactor | integer | | `4` | `1` → `1024` | yes | Specifies the scale factor for goal-driven generation resizing. | | jvm\_CMSTriggerRatio | integer | | `80` | `0` → `100` | yes | The percentage of MinHeapFreeRatio allocated before CMS GC starts | | jvm\_CMSInitiatingOccupancyFraction | integer | | `-1` | `-1` → `99` | yes | Configure oldgen occupancy fraction threshold for CMS GC. Negative values default to CMSTriggerRatio. | | jvm\_CMSClassUnloadingEnabled | categorical | | `+CMSClassUnloadingEnabled` | `+CMSClassUnloadingEnabled`, `-CMSClassUnloadingEnabled` | yes | Enables class unloading when using CMS. | | jvm\_useCMSInitiatingOccupancyOnly | categorical | | `-UseCMSInitiatingOccupancyOnly` | `+UseCMSInitiatingOccupancyOnly`, `-UseCMSInitiatingOccupancyOnly` | yes | Use of the occupancy value as the only criterion for initiating the CMS collector. | | jvm\_G1HeapRegionSize | integer | megabytes | `8` | `1`→`32` | yes | Sets the size of the regions for G1. | | jvm\_G1ReservePercent | integer | | `10` | `0` → `50` | yes | Sets the percentage of the heap that is reserved as a false ceiling to reduce the possibility of promotion failure for the G1 collector. | | jvm\_G1NewSizePercent | integer | | `5` | `0` → `100` | yes | Sets the percentage of the heap to use as the minimum for the young generation size. | | jvm\_G1MaxNewSizePercent | integer | | `60` | `0` → `100` | yes | Sets the percentage of the heap size to use as the maximum for young generation size. | | jvm\_G1MixedGCLiveThresholdPercent | integer | | `85` | `0` → `100` | yes | Sets the occupancy threshold for an old region to be included in a mixed garbage collection cycle. | | jvm\_G1HeapWastePercent | integer | | `5` | `0` → `100` | yes | The maximum percentage of the reclaimable heap before starting mixed GC. | | jvm\_G1MixedGCCountTarget | integer | collections | `8` | `0` → `100` | yes | Sets the target number of mixed garbage collections after a marking cycle to collect old regions with at most G1MixedGCLIveThresholdPercent live data. The default is 8 mixed garbage collections. | | jvm\_G1OldCSetRegionThresholdPercent | integer | | `10` | `0` → `100` | yes | The upper limit on the number of old regions to be collected during mixed GC. | ### Compilation | Name | Type | Unit | Default | Domain | Restart | Description | | --------------------------------- | ----------- | --------- | ----------------------------------------- | -------------------------------------------------- | ------- | ------------------------------------------------------------------------------------------------- | | jvm\_reservedCodeCacheSize | integer | megabytes | `240` | `3` → `2048` | yes | The maximum size of the compiled code cache pool. | | jvm\_tieredCompilation | categorical | | `+TieredCompilation` | `+TieredCompilation`, `-TieredCompilation` | yes | The type of the garbage collection algorithm. | | jvm\_tieredCompilationStopAtLevel | integer | | `4` | `0` → `4` | yes | Overrides the number of detected CPUs that the VM will use to calculate the size of thread pools. | | jvm\_compilationThreads | integer | threads | You should select your own default value. | You should select your own domain. | yes | The number of compilation threads. | | jvm\_backgroundCompilation | categorical | | `+BackgroundCompilation` | `+BackgroundCompilation`, `-BackgroundCompilation` | yes | Allow async interpreted execution of a method while it is being compiled. | | jvm\_inline | categorical | | `+Inline` | `+Inline`, `-Inline` | yes | Enable inlining. | | jvm\_maxInlineSize | integer | bytes | `35` | `1` → `2097152` | yes | The bytecode size limit (in bytes) of the inlined methods. | | jvm\_inlineSmallCode | integer | bytes | `2000` | `1` → `16384` | yes | The maximum compiled code size limit (in bytes) of the inlined methods. | ### Other parameters | Name | Type | Unit | Default | Domain | Restart | Description | | ------------------------- | ----------- | ---- | ------------------- | ---------------------------------------- | ------- | ------------------------------------------------------------------------------------------------- | | jvm\_aggressiveOpts | categorical | | `-AggressiveOpts` | `+AggressiveOpts`, `-AggressiveOpts` | yes | Turn on point performance compiler optimizations. | | jvm\_usePerfData | categorical | | `+UsePerfData` | `+UsePerfData`, `-UsePerfData` | yes | Enable monitoring of performance data. | | jvm\_useNUMA | categorical | | `-UseNUMA` | `+UseNUMA`, `-UseNUMA` | yes | Enable NUMA. | | jvm\_useBiasedLocking | categorical | | `+UseBiasedLocking` | `+UseBiasedLocking`, `-UseBiasedLocking` | yes | Manage the use of biased locking. | | jvm\_activeProcessorCount | integer | CPUs | `1` | `1` → `512` | yes | Overrides the number of detected CPUs that the VM will use to calculate the size of thread pools. | ## Domains The following parameters require their ranges or default values to be updated according to the described rules: | **Parameter** | **Default value** | **Domain** | | ------------------------- | ---------------------------------- | ---------------------------------------- | | jvm\_minHeapSize | | Depends on the instance available memory | | jvm\_maxHeapSize | | Depends on the instance available memory | | jvm\_newSize | | Depends on the configured heap | | jvm\_maxNewSize | | Depends on the configured heap | | jvm\_concurrentGCThreads | Depends on the available CPU cores | Depends on the available CPU cores | | jvm\_parallelGCThreads | Depends on the available CPU cores | Depends on the available CPU cores | | jvm\_compilation\_threads | Depends on the available CPU cores | Depends on the available CPU cores | ## Constraints The following tables show a list of constraints that may be required in the definition of the study, depending on the tuned parameters: | Formula | Notes | | ---------------------------------------------------------- | ----- | | jvm.jvm\_minHeapSize <= jvm.jvm\_maxHeapSize | | | jvm.jvm\_minHeapFreeRatio <= jvm.jvm\_maxHeapFreeRatio | | | jvm.jvm\_maxNewSize < jvm.jvm\_maxHeapSize | | | jvm.jvm\_concurrentGCThreads <= jvm.jvm\_parallelGCThreads | |