Java Heap, Stack Size, Perm Gen and Full GC tunning

A good start to understand JVM, Heap, Perm Gen and GC collector

JDK 6 Performance Features and Update

GC Collector:

Serial Collector (-XX:+UseSerialGC)

• Throughput Collectors

> Parallel Scavanging Collector for Young Gen

 -XX:+UseParallelGC

> Parallel Compacting Collector for Old Gen

 -XX:+UseParallelOldGC (on by default with ParallelGC in JDK 6)

• Concurrent Collector

> Concurrent Mark-Sweep (CMS) Collector

 -XX:+UseConcMarkSweepGC

> Concurrent (Old Gen) and Parallel (Young Gen) Collectors

 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC

• The new G1 Collector as of Java SE 6 Update 14 (-XX:+UseG1GC)

Sample JVM Parameters:

Performance Goals and Exhibits

A) High Throughput (e.g. batch jobs, long transactions)

B) Low Pause and High Throughput (e.g. portal app)

• JDK 6

A) -server -Xms2048m -Xmx2048m -Xmn1024m -XX:+AggressiveOpts

-XX:+UseParallelGC -XX:ParallelGCThreads=16

B) -server -Xms2048m -Xmx2048m -Xmn1024m -XX:+AggressiveOpts

-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:ParallelGCThreads=16

• JDK 5

A) -server -Xms2048m -Xmx2048m -Xmn1024m -XX:+AggressiveOpts

-XX:+UseParallelGC -XX:ParallelGCThreads=16 -XX:+UseParallelOldGC

-XX:+UseBiasedLocking

B) -server -Xms2048m -Xmx2048m -Xmn1024m -XX:+AggressiveOpts

-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:ParallelGCThreads=16

-XX:+UseBiasedLocking

Rule of Thumb on Best selection of

> Garbage Collector (Make sure to override GCThreads)
> Heap Size (-Xms == 1/64 Max Memory or Max Heap and
-Xmx == ¼ Max Memory or Max Heap)
> Runtime Compiler (-server vs -client)
• Desired Goals (This is a hint, not a guarantee)
> Maximum Pause Time (-XX:MaxGCPauseMillis=)
> Application Throughput (-XX:GCTimeRatio= where
Application time = 1 / (1 + n))

Do check out 1.5 paper as it comes with sample parameters for high thoughput and low latency application

Java 1.5 Tuning White Paper

If you are using 1.6, check out the difference and improvement from 1.6 paper, take note that 1.5 parameters still apply to 1.6.

Java SE 6 Performance White Paper

A very practical and easy to understandable slide which walking you through the Sun HotSpot GC tuning tip and take-away parameters.

HotSpot JVM Tuning

Wondering whether java thread stack space (Xss) and  perm gen (MaxPermSize) part of heap space. The answer is NO. That is why when u saw actually linux memory consumption is bigger than your "-Xmx" settings.

Using -Xss to adjust Java default thread stack size to save memory and prevent StackOverflowError

One working jvm parameters with JBoss server:

JAVA_OPTS="-server -Xms3072m -Xmx3072m -Xmn2048m -XX:MaxPermSize=256m -Dorg.jboss.resolver.warning=true -Dsun.rmi.dgc.client.gcInterval=3600000 -Dsun.rmi.dgc.server.gcInterval=3600000 -XX:ParallelGCThreads=8 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:SurvivorRatio=8 -XX:TargetSurvivorRatio=90 -XX:MaxTenuringThreshold=31 -XX:+AggressiveOpts -XX:+PrintHeapAtGC -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -XX:+PrintGCApplicationStoppedTime -Xloggc:/opt/jbos/server/default/log/jvmgc.log"

Diagnosing a Garbage Collection problem

You have short-term memory on Linux Shell? Never mind, just check out this article and refresh your mind.