JVM-XX: Parameter Introduction

function switch:

Parameters	default value or limit	Description
Parameters	Default value	Function
-xx:-allowusersignalhandlers	Limited to Linux and Solaris, not enabled by default	Allows the installation of signal handlers for Java processes, see class: Sun.misc.Signal, Sun.misc.SignalHandler
-xx:+disableexplicitgc	Enabled by default	Prohibit explicitly calling System.GC () at run time
-xx:+failovertooldverifier	Java6 new introduction option, enabled by default	If the new class checker fails, the old validator is used (failure reason: Because the JDK6 is most backward-compatible to JDK1.2, and JDK1.2 's class info differs greatly from the JDK6 info, the new validator may fail the checksum)
-xx:+handlepromotionfailure	Java5 previously is not enabled by default, JAVA6 is enabled by default	Closure of the new generation collection guarantee
-xx:+maxfdlimit	Limited to Solaris, enabled by default	Set the Java process available file descriptor to the maximum allowable value for the operating system.
-xx:preblockspin=10	-xx:+usespinning must be enabled first, it has been enabled by default for JAVA6, the default spin 10 times	Control spin times for multi-threaded spin lock optimization
-xx:-relaxaccesscontrolcheck	Not enabled by default	In the class validator, the check for access control is relaxed, and the effect is similar to the setaccessible in reflection
-xx:+scavengebeforefullgc	Enabled by default	Triggering a minor GC before the full GC
-xx:+usealtsigs	Limited to Solaris, enabled by default	To prevent conflicts with other applications that send signals, alternate signals are allowed to replace SIGUSR1 and SIGUSR2
-xx:+useboundthreads	Limited to Solaris, enabled by default	Binds all user threads to kernel threads, reducing the number of threads entering starvation (no CPU time)
-xx:-useconcmarksweepgc	Not enabled by default	Enable the CMS low-pause garbage collector to reduce FGC pause time
-xx:+usegcoverheadlimit	Enabled by default	Limit the elapsed time of the GC. If the GC takes too long, it will throw an oom
-xx:+uselwpsynchronization	Limited to Solaris, enabled by default	Replace thread synchronization with lightweight processes (kernel threads)
-xx:-useparallelgc	-server when enabled, in other cases, not enabled by default	Strategy for Cenozoic use of parallel cleanup, old generation using single-threaded mark-sweep-compact garbage collector
-xx:-useparalleloldgc	Not enabled by default	A garbage collector that uses parallel cleanup for both the old and the new generation
-xx:-useserialgc	-client when enabled, in other cases, not enabled by default	Using the serial garbage collector
-xx:-usespinning	java1.4.2 and 1.5 need to be enabled manually, JAVA6 is enabled by default	Enable multi-threaded spin lock optimization
-xx:+usetlab	1.4.2 before and when using the-client option, the default is not enabled and the remaining versions are enabled by default	Enable thread Local cache
-xx:+usesplitverifier	Java5 is not enabled by default, JAVA6 is enabled by default	Using the new class type validator
-xx:+usethreadpriorities	Enabled by default	Use the priority of the local thread
-xx:+usevminterruptibleio	Limited to Solaris, enabled by default	In Solaris, allow thread break in runtime

Performance parameters:

Parameters	default value or limit	Description
-xx:+aggressiveopts	Introduced after JDK 5 update 6, but needs to be enabled manually, JDK6 is enabled by default	Enable the latest tuning results for the JVM development team. such as compilation optimization, bias lock, parallel old generation collection, etc.
-xx:compilethreshold=10000	1000	By JIT compiler, the method is compiled into machine code trigger threshold, can be understood as the number of times to call the method, such as 1000 times, the method is compiled into machine code
-xx:largepagesizeinbytes=4m	Default 4m, AMD64 bit: 2m	Set the memory page size for heap memory
-xx:maxheapfreeratio=70	70	After GC, if the free heap memory is found to occupy 70% of the entire estimated upper limit, the estimated upper limit value is shrunk
-xx:maxnewsize=size	1.3.1 Sparc:32m, 1.3.1 X86:2.5m	The new generation accounts for the maximum value of the entire heap memory
-xx:maxpermsize=64m	After 5.0: The 30%, 1.4 amd64:96m, 1.3.1-client:32m, other default 64m	Perm (commonly known as the method area) represents the maximum value of the entire heap memory
-xx:minheapfreeratio=40	40	After GC, increase the upper limit if you find that free heap memory accounts for 40% of the total estimated upper value
-xx:newratio=2	Sparc-client:8, X86-server:8, X86-client:12,-client:4 (1.3), 8 (1.3.1+), X86:12, other default 2	The heap memory footprint of the Cenozoic and older generations, for example, 2 means that the Cenozoic represents 1/2 of the older generation, accounting for 1/3 of the total heap memory
-xx:newsize=2.125m	After 5.0: The 2.125m bit Vms will increase the default value of 30%, X86:1M, x86, 5.0 after: 640k	Default value for new generation estimation caps
-xx:reservedcodecachesize=32m	Solaris 64-bit, AMD64,-server x86:48m, 1.5.0_06, Solaris 64-bit amd64:1024m, other default 32m	Set the maximum value of the code cache, compile-time with
-xx:survivorratio=8	Solaris Amd64:6, Sparc in 1.3.1:25, Solaris platforms 5.0 before: 32, other default 8	The occupancy ratio of Eden to survivor. For example, 8 indicates that a survivor area occupies 1/8 of the Eden Memory, or 1/10 of the Cenozoic memory, why not 1/9? Because our new generation has 2 survivor, namely S0 and S1. So survivor is a total of 8/10 of the 2/10,eden and Cenozoic of the Cenozoic memory.
-xx:targetsurvivorratio=50	50	The actual amount of survivor space used. Default is 50%, up to 90%
-xx:threadstacksize=512	sparc:512, Solaris x86:320 (5.0 ago), Sparc bit:1024, Linux amd64:1024 (5.0 ago 0), other default 512.	Thread stack size
-xx:+usebiasedlocking	Introduced after JDK 5 update 6, but needs to be enabled manually, JDK6 is enabled by default	Enable biased locking
-xx:+usefastaccessormethods	Enabled by default	Optimize Getter method performance for primitive types (get/set:primitive type)
-xx:-useism	Enabled by default	Enable Solaris for ISM
-xx:+uselargepages	Introduced after JDK 5 update 5, but needs to be enabled manually, JDK6 is enabled by default	Enable Large Memory Paging
-xx:+usempss	Before 1.4.1: Not enabled, the remaining versions are enabled by default	Solaris MPSS is enabled and cannot be used concurrently with ISM
-xx:+usestringcache	Enabled by default	Enables caching of commonly used strings.
-xx:allocateprefetchlines=1	1	Number of cache lines to load after the last object allocation using prefetch instructions generated in JIT compiled code. Default values is 1 if the last allocated object is an instance and 3 if it is an array.
-xx:allocateprefetchstyle=1	1	Generated code style for prefetch instructions. 0–no prefetch instructions is generate*d*, 1–execute prefetch instructions after each allocation, 2–use Tlab allocation watermark Pointer to gate when prefetch instructions is executed.
-xx:+usecompressedstrings	Java 6 Update 21 has an option	For strings that do not require 16-bit characters, you can use byte[] rather than char[]. For many applications, this saves memory but slows down (5%-10%)
-xx:+optimizestringconcat	Introduced in Java 6 update 20	Optimize string connection operations where possible

Debug Parameters:

Parameters	default value or limit	Description
-xx:-citime		The time that the issuance fee was JIT compiled
-xx:errorfile=./hs_err_pid<pid>.log	Introduced in JDK6	Error file
-xx:-extendeddtraceprobes	JDK6 is introduced only in the Solaris	Enable performance impact of DTrace probes
-xx:heapdumppath=./java_pid<pid>.hprof	1.4.2 Update, 5.0 update 7	Specifies the file path or directory of the Heapdump
-xx:-heapdumponoutofmemoryerror	1.4.2 Update, 5.0 update 7	Heapdump when an oom is thrown
-xx:onerror= "<cmd args>;<cmd args>"	1.4.2 Update 9	Execute user-specified commands when an error occurs
-xx:onoutofmemoryerror= "<cmd args>; <cmd args> "	1.4.2 Update 12, 6	Execute user-specified commands when oom occurs
-xx:-P Rintclasshistogram	1.4.2	Print class instance information when ctrl+break occurs, same as Jmap-histo
-xx:-P Rintconcurrentlocks	6	Print java.util.concurrent lock information when ctrl+break occurs, same as Jstack-l
-xx:-P Rintcommandlineflags	5	Print markup on the command line
-xx:-P rintcompilation		Print information When the method is compiled
-xx:-P RINTGC		Print information when GC occurs
-xx:-P Rintgcdetails	1.4.0	Print GC Details
-xx:-P Rintgctimestamps	1.4.0	Print GC Time
-xx:-P rinttenuringdistribution		Print tenuring Age Information
-xx:-traceclassloading		Tracking class loading
-xx:-traceclassloadingpreorder	1.4.2	Keep track of all loaded reference classes
-xx:-traceclassresolution	1.4.2	Track changes in constant pools
-xx:-traceclassunloading		Unloading of trace classes
-xx:-traceloaderconstraints	6	Trace Recording of loader constraints
-xx:+perfsavedatatofile		Save Jvmstat Binary when exiting
-xx:parallelgcthreads=		Set the number of threads for the parallel garbage collector between the Cenozoic and the older generations
-xx:+usecompressedoops		Enables the use of compressed pointers (object references represented as + bit offsets instead of 64-bit pointers) for op Timized 64-bit Performance with Java heap sizes less than 32GB.
-xx:+alwayspretouch		Pre-touch the Java heap during JVM initialization. Every page of the heap is thus demand-zeroed during initialization rather than incrementally during application execution.
-xx:allocateprefetchdistance=		Sets the prefetch distance for object allocation. Memory about-to-being written with the value of new objects are prefetched into caches at this distance (in bytes) beyond the A Ddress of the last allocated object. Each Java thread have its own allocation point. The default value varies with the platform on which, the JVM is running.
-xx:inlinesmallcode=		Inline compiled code when the compiled code is less than the specified value
-xx:maxinlinesize=35		Maximum number of bytes in an inline method
-xx:freqinlinesize=		Maximum bytecode size for a method that is frequently implemented inline
-xx:loopunrolllimit=		Unroll loop bodies with server compiler intermediate representation node count less than this value. The limit used by the server compiler are a function of this value, not the actual value. The default value varies with the platform on which, the JVM is running.
-xx:initialtenuringthreshold=7		Sets the maximum number of initial objects to survive in the Cenozoic
-xx:maxtenuringthreshold=		Set the maximum number of objects to survive in the Cenozoic, Max 15, parallel recycle mechanism default to 15,CMS default is 4

JVM-XX: Parameter Introduction (RPM)