Client and server working modes of JVM

【README】

JVM Server Patterns and client mode , The main difference is ：

-Server When mode starts , Slower , But once it's up and running , Performance will be greatly improved .

as a result of : When the virtual machine is running -client In mode , The code used is C1 The lightweight compiler for , and -server The virtual machine started in mode is relatively heavyweight , code-named C2 The compiler . C2 Than C1 Compiler compilation is relatively thorough ,, After the service , Higher performance .　　

java -version You can see directly that you are using client still server ​

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【1】client

    C:\Documents and Settings\Administrator>java -version  
    java version "1.6.0_21"  
    Java(TM) SE Runtime Environment (build 1.6.0_21-b06)  
    Java HotSpot(TM) Client VM (build 17.0-b16, mixed mode, sharing)  

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【2】server

 [[email protected] ~]# java -version  
    java version "1.6.0_06"  
    Java(TM) SE Runtime Environment (build 1.6.0_06-b02)  
    Java HotSpot(TM) Server VM (build 10.0-b22, mixed mode)  

The two modes can be switched by changing the configuration (jvm.cfg The configuration file ) To achieve :
32 Bit virtual machine in directory JAVA_HOME/jre/lib/i386/jvm.cfg,
64 The position is JAVA_HOME/jre/lib/amd64/jvm.cfg, at present 64 Bit only supported server Pattern , The configuration contents are as follows

   -server KNOWN  
    -client KNOWN  
    -hotspot ALIASED_TO -client  
    -classic WARN  
    -native ERROR  
    -green ERROR  

When JVM Used to start GUI The interface is suitable for interactive application client Pattern , When JVM Recommended for running server daemons Server Pattern .
JVM stay client Mode default -Xms yes 1M,-Xmx yes 64M;JVM stay Server Mode default -Xms yes 128M,-Xmx yes 1024M. We can run :java -version Check it out. jvm What mode does the default work in .

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【3】 Command line

【3.1】-Xms

Sets the initial size of the available memory heap for the virtual machine , The default unit is bytes , The size is 1024 And greater than 1MB, You can use k(K) or m(M) To set a large amount of memory in units . The initial heap size is 2MB.
for example ：-Xms6400K,-Xms256M

【3.2】-Xmx

Set the maximum available size of the virtual machine memory heap , The default unit is bytes . The value must be 1024 An integral multiple , And it's bigger than 2MB. You can use k(K) or m(M) To set a large amount of memory in units . The default heap maximum is 64MB.
for example ：-Xmx81920K,-Xmx80M

【3.3】-Xloggc:

Write the information of each garbage collection of the virtual machine to the log file , The file name is from file Appoint , The file format is flat file , Content and -verbose:gc The output is the same .

【3.4】-client,-server

These two parameters are used to set the running mode of the virtual machine ,client Mode starts faster , But runtime performance and memory management are not as efficient as server Pattern , Usually used for client applications . contrary ,server Mode startup is better than client slow , But higher performance can be achieved .

Add ： And client Compared to model , server Patterns do more compiler optimization , Such as instruction reordering ;
 

Summary ：

stay windows On , The default virtual machine type is client Pattern ;

If you want to use server Pattern , It needs to be added when starting the virtual machine -server Parameters , For better performance , Apply to the server side , Recommend server Pattern , Especially more than one CPU The system of , Higher performance achieved . stay Linux,Solaris By default server Pattern .