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JVM - common parameters

2022-04-23 10:31:00 【Xiaoxian.】

One 、 Parameter query

 perform ：
  java -XX:+PrintFlagsFinal
 Be careful ：
  =		 Represents the default value 
  :=	 Said by JVM Or the value modified by the user

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Two 、 Parameter classification

1、 Standard parameters

-version 
-help 
-server 
-cp

2、-X Parameters （ Nonstandard ,JDK There may be changes in various versions ）

-Xint 	 Explain to perform  
-Xcomp 	 Compile it into local code for the first time  
-Xmixed  Mixed mode ,JVM Decide for yourself

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3、-XX Parameters （ Nonstandard , Relatively unstable , It is mainly used for JVM tuning ）

1）Boolean type

 Format ：
  -XX:[+-]<name>
 Be careful ：
  +  Means to enable name attribute  
  -  Disable name attribute 
 Example ：
  -XX:+UseConcMarkSweepGC  Means to enable CMS Type of garbage collector  
  -XX:+UseG1GC 						 Means to enable G1 Type of garbage collector

2） Not Boolean type

 Format ：
  -XX<name>=<value>
 Be careful ：
  name The value of the property is value
 Example ：
  -XX:MaxGCPauseMillis=500

4、 The other parameters （ Short for parameters ）

-Xms1000M	 Equivalent to 	-XX:InitialHeapSize=1000M
-Xmx1000M	 Equivalent to 	-XX:MaxHeapSize=1000M
-Xss100		 Equivalent to 	-XX:ThreadStackSize=100

3、 ... and 、 Common parameters

Parameters	meaning	explain
-XX:CICompilerCount=3	Maximum number of parallel compilations	If the setting is greater than 1, Although the compilation speed will increase , But it also affects the stability of the system , Will increase JVM Possibility of collapse
-XX:InitialHeapSize=100M	Initialize heap size	Abbreviation -Xms100M
-XX:MaxHeapSize=100M	Maximum heap size	Abbreviation -Xms100M
-XX:NewSize=20M	Set the size of the younger generation
-XX:MaxNewSize=50M	The largest size of the younger generation
-XX:OldSize=50M	Set the age size
-XX:MetaspaceSize=50M	Set method area size
-XX:MaxMetaspaceSize=50M	Maximum size of method area
-XX:+UseParallelGC	Use UseParallelGC	The new generation , Throughput priority
-XX:+UseParallelOldGC	Use UseParallelOldGC	Old age , Throughput priority
-XX:+UseConcMarkSweepGC	Use CMS	Old age , Pause time first
-XX:+UseG1GC	Use G1GC	The new generation , Old age , Pause time first
-XX:NewRatio	The ratio of the new generation to the old generation	such as -XX:Ratio=4, It means Cenozoic : Old age =1:4, That is, the Cenozoic accounts for the whole heap memory 1/5
-XX:SurvivorRatio	Two S Area and Eden Area ratio	such as -XX:SurvivorRatio=8, That is to say (S0+S1):Eden=2:8, That's one S Of the whole Cenozoic 1/10
-XX:+HeapDumpOnOutOfMemoryError	Start heap memory overflow printing	When JVM When heap memory overflows , That is to say OOM, Automatic generation dump file
-XX:HeapDumpPath=heap.hprof	Specifies the heap memory overflow print directory	Indicates that a... Is generated in the current directory heap.hprof file
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -Xloggc:g1-gc.log	Print out GC journal	Different garbage collectors can be used , Contrast check GC situation
-Xss128k	Set the stack size for each thread	The empirical value is 3000-5000 The best
-XX:MaxTenuringThreshold=6	Increase the maximum critical value of the elderly	The default value is 15
-XX:InitiatingHeapOccupancyPercent	Start concurrency GC The proportion of heap memory used during the cycle	G1 Garbage collectors like that use it to trigger concurrency GC cycle , Based on the utilization of the whole heap , It's not just a generation of memory usage ratio . The value is 0 said ” Has been performed GC loop ”. The default value is 45
-XX:G1HeapWastePercent	Percentage of allowed wasted heap space	The default is 10%, If the recyclable space of concurrent tags is less than 10%, It doesn't trigger MixedGC.
-XX:MaxGCPauseMillis=200ms	G1 Maximum pause time	The pause time cannot be too small , Too small will lead to G1 Can't keep up with the speed of garbage . Eventually degenerated into FullGC. So tuning this parameter is a continuous process , Gradually adjust to the best .
-XX:ConcGCThreads=n	The number of threads used by the concurrent garbage collector	The default value follows JVM Running on different platforms
-XX:G1MixedGCLiveThresholdPercent=65	Old areas to be included in the mixed waste recycling cycle	Set the occupancy threshold for the domain. The default occupancy is 65%
-XX:G1MixedGCCountTarget=8	After setting the marking cycle , The upper limit for survival data is G1MixedGCLIveThresholdPercent The target number of times to perform mixed garbage collection in the old area of	Default 8 Secondary mixed waste recycling , The goal of mixed recycling is to control within this target number
-XX:G1OldCSetRegionThresholdPercent=1	describe Mixed GC when ,OldRegion Be added to CSet in	By default ,G1 Only 10% Of OldRegion Add to CSet in

Four 、 Common ways to set parameters

1、 development tool ：IDEA,eclipse
2、 function jar：java -XX:+UseG1GC xxx.jar
3、Web Containers ：tomcat Script
4、 adopt jinfo Adjust something in real time java Process parameters ( The parameter is only marked manageable Of flags Can be modified in real time )

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