6 Command-Line Options

This topic describes the various HotSpot command-line options and compares them with those available in Oracle JRockit:

Mapping of Oracle JRockit to HotSpot Command-Line Options

Certain Oracle JRockit command-line options are similar to HotSpot options.

This section provides either a one-to-one mapping of Oracle JRockit options to HotSpot options, or refers you to other sections of this document. There are certain Oracle JRockit options for which there are no corresponding HotSpot JVM options. Also, some of the mapped HotSpot options aren’t exactly equivalent to the Oracle JRockit options and may provide slightly different behavior on the HotSpot.

When migrating, simply translating every option used with Oracle JRockit into similar HotSpot options isn’t recommended. Especially for performance-related options, the best practice is to start by only specifying the Java heap size and the garbage collector, such as CMS or G1. Any additional tuning for HotSpot, if necessary, must be done based on new benchmarking and profiling done with HotSpot. It isn’t advised to assume that most, if any, JVM-level tuning decisions made for an Oracle JRockit configuration will also apply to a HotSpot configuration.

Table 6-1 -X Command-Line Options

Oracle JRockit	HotSpot	Notes
`-Xbootclasspath`	Same	NA
`-Xbootclasspath/a`	Same	NA
`-Xbootclasspath/p`	Same	NA
`-Xcheck:jni`	Same	NA
`-Xdebug`	Same	NA
`-Xgc`	NA	See Tuning Garbage Collection.
`-XgcPrio` (deprecated)	NA	See Garbage Collectors.
`-XlargePages`	`-XX:+UseLargePages`	NA
`-Xmanagement`	NA	NA
`-Xms`	Same	NA
`-Xmx`	Same	NA
`-XnoClassGC` (deprecated)	Same	Don’t use, except for troubleshooting.
`-XnoOpt`	NA	See Compilation Optimization.
`-Xns`	Same	NA
`-XpauseTarget`	`-XX:MaxGCPauseMillis=n`	See Garbage Collectors.
`-Xrs`	Same	NA
`-Xss`	Same	NA
`-XstrictFP`	NA	NA
`-Xverbose`	`-verbose`	See Logging.
`-Xverbosedecorations`	NA	See Logging.
`-XverboseLog`	NA	See Logging.
`-XverboseTimeStamp`	NA	See Logging.
`-Xverify`	Same	NA

Table 6-2 -XX Command-Line Options

Oracle JRockit	HotSpot	Notes on HotSpot Options
`-XXaggressive`	`-XX:+AggressiveHeap` `-XX:+AggressiveOpts`	`-XX:+AggressiveHeap` enables Java heap optimization. This sets various parameters to be optimal for long-running jobs with intensive memory allocation, based on the configuration of the computer (RAM and CPU). By default, the option is disabled and the heap isn’t optimized. `-XX:+AggressiveOpts` enables other non-heap related optimization.
`-XX:AllocChunkSize`	Related options: `-XX:AllocateInstancePrefetchLines=<lines>` `-XX:AllocatePrefetchDistance=<size>` `-XX:AllocatePrefetchInstr=<instruction>` `-XX:AllocatePrefetchLines=<lines>` `-XX:AllocatePrefetchStepSize=<size>` `-XX:AllocatePrefetchStyle=<style>`	NA
`-XX:+\|-CheckJNICalls`	`-Xcheck:jni`	NA
`-XX:+\|-CheckStacks`	NA	NA
`-XXcompaction`	NA	NA
`-XXcompactRatio` (deprecated)	NA	NA
`-XXcompactSetLimit` (deprecated)	NA	NA
`-XXcompactSetLimitPerObject` (deprecated)	NA	NA
`-XXcompressedRefs`	`-XX:-UseCompressedOops`	See Runtime Options.
`-XX:+\|-CrashOnOutOfMemoryError`	Same	NA
`-XX:+\|-DisableAttachMechanism`	Same	NA
`-XXdumpFullState`	NA	On the HotSpot side, there is an option `CreateMinidumpOnCrash` to enable the dumping of minidumps when fatal errors occur on the Windows platform.
`-XXdumpSize`	NA	NA
`-XX:ExceptionTraceFilter`	NA	NA
`-XX:+\|-ExitOnOutOfMemoryError`	Same	NA
`-XX:ExitOnOutOfMemoryErrorExitCode`	NA	NA
`-XXexternalCompactRatio` (deprecated)	NA	NA
`-XX:+\|-FailOverToOldVerifier`	Same	NA
`-XX:+\|-FlightRecorder`	Same	Enables the use of the Java Flight Recorder (JFR) during the runtime of the application. This is a commercial feature that requires you to also specify the `-XX:+UnlockCommercialFeatures` option.
`-XX:FlightRecorderOptions`	Same	NA
`-XX:+\|-FlightRecordingDumpOnUnhandledException`	NA	NA
`-XX:FlightRecordingDumpPath`	NA	NA
`-XXfullSystemGC`	Related options: `-XX:+DisableExplicitGC` `-XX:+ExplicitGCInvokesConcurrent` `-XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses`	See Garbage Collectors.
`-XXgcThreads`	Related options: `-XX:ParallelGCThreads=<threads>` `-XX:ConcGCThreads=<threads>`	See Garbage Collectors.
`-XX:GCTimePercentage`	NA	NA
`-XX:GCTimeRatio`	NA	NA
`-XXgcTrigger`	Related options: `-XX:CMSInitiatingOccupancyFraction=<percent`> `-XX:CMSTriggerRatio=<percent>`	See Garbage Collectors.
`-XX:+\|-HeapDiagnosticsOnOutOfMemoryError`	Can achieve the same by using `-XX:OnOutOfMemoryError=<command>`	Example: `java -XX:OnOutOfMemoryError="jmap -heap %p" JavaProgram`
`-XX:HeapDiagnosticsPath`	NA	NA
`-XX:+\|-HeapDumpOnCtrlBreak`	NA	NA
`-XX:+\|-HeapDumpOnOutOfMemoryError`	Same	NA
-`XX:HeapDumpPath`	Same	NA
`-XX:HeapDumpSegmentSize`	NA	NA
`-XXheapParts` (deprecated)	NA	NA
`-XXinternalCompactRatio` (deprecated)	NA	NA
`-XX:+\|-JavaDebug`	NA	NA
`-XXkeepAreaRatio`	`XX:SurvivorRatio=<ratio>`	Sets the ratio between the eden space size and the survivor space size. By default, this option is set to 8. There is another option `-XX:InitialSurvivorRatio=ratio` to set the initial survivor space ratio used by the throughput garbage collector. Adaptive sizing is enabled by default with the throughput garbage collector by using the `-XX:+UseParallelGC` and `-XX:+UseParallelOldGC` options, and the survivor space is resized according to the application behavior, starting with this initial value.
`-XXlargeObjectLimit` (deprecated)	NA	NA
`-XX:MaxCodeMemory`	`-XX:ReservedCodeCacheSize=<size`>	See Compilation Optimization.
`-XX:MaxDirectMemorySize`	Same	NA
`-XX:MaximumNurseryPercentage`	`-XX:NewRatio=<ratio>`	Sets the ratio between young and old generation sizes. By default, this option is set to 2.
`-XX:MaxLargePageSize`	`-XX:LargePageSizeInBytes=<size`>	See Runtime options.
`-XX:MaxRecvBufferSize`	NA	NA
`-XXminBlockSize` (deprecated)	NA	NA
`-XXnoSystemGC`	Related options: `-XX:+DisableExplicitGC` `-XX:+ExplicitGCInvokesConcurrent` `-XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses`	See Garbage Collectors.
`-XX:OptThreads`	`-XX:CICompilerCount=threads`	See Compilation Optimization.
`-XX:+\|-RedoAllocPrefetch`	Related options: `-XX:AllocateInstancePrefetchLines=<lines`> `-XX:AllocatePrefetchDistance=<size`> `-XX:AllocatePrefetchInstr=<instruction`> `-XX:AllocatePrefetchLines=<lines`> `-XX:AllocatePrefetchStepSize=<size>` `-XX:AllocatePrefetchStyle=<style`>	NA
`-XX:+\|-ReserveCodeMemory`	`-XX:ReservedCodeCacheSize=<size>`	See Compilation Optimization.
`-XX:SegmentedHeapDumpThreshold`	NA	NA
`-XXsetGC` (deprecated)	NA	NA
`-XX:+\|-StrictFP`	NA	NA
`-XX:StartFlightRecording`	Same	NA
`-XXtlaSize`	`XX:TLABSize=<size>`	Sets the initial size (in bytes) of a thread-local allocation buffer (TLAB). If this option is set to 0, then the JVM chooses the initial size automatically.
`-XX:TreeMapNodeSize`	NA	NA
`-XX:+\|-UseAdaptiveFatSpin`	NA	NA
`-XX:+\|-UseAllocPrefetch`	Related options: `-XX:AllocateInstancePrefetchLines=<lines>` `-XX:AllocatePrefetchDistance=<size>` `-XX:AllocatePrefetchInstr=<instruction>` `-XX:AllocatePrefetchLines=<lines>` `-XX:AllocatePrefetchStepSize=<size>` `-XX:AllocatePrefetchStyle=<style`	NA
`-XX:+\|-UseCallProfiling`	`-XX:+UseTypeProfile`	NA
`-XX:+\|-UseCfsAdaptedYield`	NA	NA
`-XX:+\|-UseClassGC`	-`Xnoclassgc`	Disables garbage collection (GC) of classes. This can save the GC time, which shortens interruptions during the application run. When you specify `Xnoclassgc` at startup, the class objects in the application will be left untouched during GC and will always be considered active.
`-XX:+\|-UseCPoolGC`	NA	NA
`-XX:+\|-UseFastTime`	NA	NA
`-XX:+\|-UseFatSpin`	NA	NA
`-XX:+\|-UseLargePagesFor[Heap\|Code]`	`-XX:+UseLargePages` `-XX:+UseLargePagesInMetaspace`	See Runtime Options.
`-XX:+\|-UseLazyUnlocking`	`-XX:+UseBiasedLocking`	See Runtime Options.
`-XX:+\|-UseLockProfiling`	NA	NA
`-XX:+\|-UseLowAddressForHeap`	NA	No direct corresponding option available in HotSpot but the low heap base can be specified explicitly using `HeapBaseMinAddress` option.
`-XX:+\|-UseNewHashFunction`	Same	Only relevant for JDK 5. This option must not be used on JDK 6 or later versions.
`-XX:+\|-UseThreadPriorities`	Same	On HotSpot, this option is enabled by default for the Windows platform. On JRockit, this option is disabled by default for the Windows platform.

Table 6-3 Diagnostic Commands

Oracle JRockit	HotSpot
`check_flightrecording`	`JFR.check`
`command_line`	`VM.command_line`
`dump_flightrecording`	`JFR.dump`
`exception_trace_filter`	NA
`force_crash`	NA
`heap_diagnostics`	`GC.heap_info`
`help`	`help`
`hprofdump`	`GC.heap_dump`
`kill_management_server`	`ManagementAgent.stop`
`list_vmflags`	`VM.flags`
`lockprofile_print`	NA
`lockprofile_reset`	NA
`memleakserver`	NA
`print_class_summary`	`GC.class_stats`
`print_exceptions`	NA
`print_memusage`	`VM.native_memory`
`print_object_summary`	`GC.class_histogram`
`print_threads`	`Thread.print`
`print_utf8pool`	`VM.stringtable` and `VM.symboltable`
`print_vm_state`	`VM.info`
`runsystemgc`	`GC.run`
`set_filename`	NA
`start_flightrecording`	`JFR.start`
`start_management_server`	`ManagementAgent.start` `ManagementAgent.start_local`
`stop_flightrecording`	`JFR.stop`
`stop_management_server`	`ManagementAgent.stop`
`timestamp`	NA
`verbosity`	NA
`version`	`VM.version`

jcmd Commands

The following are the list of jcmd commands:

JFR.configure
JFR.stop
JFR.start
JFR.dump
JFR.check
VM.log
VM.native_memory
VM.check_commercial_features
VM.unlock_commercial_features
ManagementAgent.status
ManagementAgent.stop
ManagementAgent.start_local
ManagementAgent.start
Compiler.directives_clear
Compiler.directives_remove
Compiler.directives_add
Compiler.directives_print
VM.print_touched_methods
Compiler.codecache
Compiler.codelist
Compiler.queue
VM.classloader_stats
Thread.print
JVMTI.data_dump
JVMTI.agent_load
VM.stringtable
VM.symboltable
VM.class_hierarchy
GC.class_stats
GC.class_histogram
GC.heap_dump
GC.finalizer_info
GC.heap_info
GC.run_finalization
GC.run
VM.info
VM.uptime
VM.dynlibs
VM.set_flag
VM.flags
VM.system_properties
VM.command_line
VM.version help

For the complete list of commands, refer to jcmd Commands in the Java Platform, Standard Edition Tools Reference guide.