http://java.sun.com/docs/hotspot/gc/ http://edocs.bea.com.cn/wls/docs92/perform/JVMTuning.html http://java.sun.com/j2se/1.4.2/docs/tooldocs/windows/java.html http://java.sun.com/j2se/1.5.0/docs/guide/vm/gc-ergonomics.html

Default max heap of Sun JDK version early than 1.5 is 64 MB, at 1.5 it can grow up to 1GB. Specifying -Xmx only has no side effects to -Xms. eg -Xmx800M the the process is still using a little memory while start up.

谢谢楼上的补充！

3000m的内存是不是太大了？能充分利用吗？还有核心堆栈内存是不是也需要设置一下呢？

java -X
-Xmixed mixed mode execution (default)
-Xint interpreted mode execution only
-Xbootclasspath:<directories and zip/jar files separated by :>
set search path for bootstrap classes and resources
-Xbootclasspath/a:<directories and zip/jar files separated by :>
append to end of bootstrap class path
-Xbootclasspath/p:<directories and zip/jar files separated by :>
prepend in front of bootstrap class path
-Xnoclassgc disable class garbage collection
-Xincgc enable incremental garbage collection
-Xloggc:<file> log GC status to a file with time stamps
-Xbatch disable background compilation
-Xms<size> set initial Java heap size
-Xmx<size> set maximum Java heap size
-Xss<size> set java thread stack size
-Xprof output cpu profiling data
-Xfuture enable strictest checks, anticipating future default
-Xrs reduce use of OS signals by Java/VM (see documentation)
-Xcheck:jni perform additional checks for JNI functions
-Xshare:off do not attempt to use shared class data
-Xshare:auto use shared class data if possible (default)
-Xshare:on require using shared class data, otherwise fail.

这些是在什么地方设置啊 到那里去设置啊

/usr/local/jdk/bin/java -Dresin.home=/usr/local/resin -server -Xms1800M -Xmx1800M -Xmn300M -Xss512K -XX:PermSize=300M -XX:MaxPermSize=300M -XX:SurvivorRatio=8 -XX:MaxTenuringThreshold=5 -XX:GCTimeRatio=19 -Xnoclassgc -XX:+DisableExplicitGC -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:+UseCMSCompactAtFullCollection -XX:CMSFullGCsBeforeCompaction=0 -XX:-CMSParallelRemarkEnabled -XX:CMSInitiatingOccupancyFraction=70 -XX:SoftRefLRUPolicyMSPerMB=0 -XX:+PrintClassHistogram -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -Xloggc:log/gc.log

我的配置，网站shedewang.com，72小时之内没有任何停顿。但是还是要考虑到不同情况，多看看gc日志堆栈的变化，有问题用jstack，jmap等工具查看哪些地方出了问题，这样可以更快的作出优化。

实践是检验真理的唯一标准。