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java JVM 参数设置

2010-08-13 16:48:23| 分类： jvm | 标签： |举报 |字号大中小订阅

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1: heap size
a: -Xmx
指定jvm的最大heap大小,如:-Xmx2g

b: -Xms
指定jvm的最小heap大小,如:-Xms1g

c: -Xmn
指定jvm中New Generation的大小,如:-Xmn256m

d: -XX:PermSize
指定jvm中Perm Generation的最小值,如:-XX:PermSize=32m

e: -XX:MaxPermSize
指定Perm Generation的最大值,如:-XX:MaxPermSize=64m

f: -Xss
指定线程桟大小,如:-Xss128k

g: -XX:NewRatio
指定jvm中Old Generation heap size与New Generation的比例,在使用CMS GC的情况下此参数失效, 如:-XX:NewRatio=2

h: -XX:SurvivorRatio
指定New Generation中Eden Space与一个Survivor Space的heap size比例,-XX:SurvivorRatio=8,那么在总共New Generation为10m的情况下,Eden Space为8m

i: -XX:MinHeapFreeRatio
指定jvm heap在使用率小于n的情况下,heap进行收缩,Xmx==Xms的情况下无效,如:-XX:MinHeapFreeRatio=30

j: -XX:MaxHeapFreeRatio
指定jvm heap在使用率大于n的情况下,heap进行扩张,Xmx==Xms的情况下无效,如:-XX:MaxHeapFreeRatio=70

k: -XX:LargePageSizeInBytes
指定Java heap的分页页面大小,如:-XX:LargePageSizeInBytes=128m

2: garbage collector
a: -XX:+UseParallelGC
指定在New Generation使用parallel collector,并行收集,同时启动多个垃圾回收thread,不能和CMS gc一起使用.系统吨吐量优先,但是会有较长长时间的app pause,后台系统任务可以使用此gc

b: -XX:ParallelGCThreads
指定parallel collection时启动的thread个数,默认是物理processor的个数,如:-xx:ParallelGCThreads=8

c: -XX:+UseParallelOldGC
指定在Old Generation使用parallel collector

d: -XX:+UseParNewGC
指定在New Generation使用parallel collector,是UseParallelGC的gc的升级版本,有更好的性能或者优点,可以和CMS gc一起使用

e: -XX:+CMSParallelRemarkEnabled
在使用UseParNewGC的情况下,尽量减少mark的时间

f: -XX:+UseConcMarkSweepGC
指定在Old Generation使用concurrent cmark sweep gc,gc thread和app thread并行,所以称作concurrent.app pause时间较短,适合交互性强的系统,如web server

g: -XX:+UseCMSCompactAtFullCollection
在使用concurrent gc的情况下,防止memory fragmention,对live object进行整理,使memory碎片减少

h: -XX:CMSInitiatingOccupancyFraction=n
指示在old generation在使用了n%的比例后,启动concurrent collector,默认值是68,如:-XX:CMSInitiatingOccupancyFraction=70
有个bug,在低版本的jvm上出现,http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6486089

i: -XX:+UseCMSInitiatingOccupancyOnly
指示只有在old generation在使用了初始化的比例后concurrent collector启动收集

3:others
a: -XX:MaxTenuringThreshold
指定一个object在经历了n次young gc后转移到old generation区,在linux64的java6下默认值是15,此参数对于throughput collector无效,如:-XX:MaxTenuringThreshold=31

b: -XX:+DisableExplicitGC
禁止java程序中的full gc,如System.gc()的调用

c: -XX:+UseFastAccessorMethods
原始类型get,set方法的优化

d: -XX:+PrintGCDetails
打应垃圾收集的情况如:
[GC 15610.466: [ParNew: 229689K->20221K(235968K), 0.0194460 secs] 1159829K->953935K(2070976K), 0.0196420 secs]

e: -XX:+PrintGCTimeStamps
打应垃圾收集的时间情况,如:
[Times: user=0.09 sys=0.00, real=0.02 secs]

f: -XX:+PrintGCApplicationStoppedTime
打应垃圾收集时,系统的停顿时间,如:
Total time for which application threads were stopped: 0.0225920 seconds

4 -XX:+UseCompressedOops
压缩指针 64位机器，JDK1.6支持

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