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We have recently migrated a large, high demand web application to Tomcat 5.5 from Tomcat 4 and have noticed some peculiar slowdown behavior that appears to be related to JVM pauses. In order to run our application and support increased load over time on Tomcat 4, many not so standard JVM parameters were set and tuned as per the below, and I am hoping someone with Tomcat JVM tuning experience can comment on anything that would likely be detrimental to a Tomcat 5.5 install. Note also that some of these could be carry over from previous versions of Java (we were running Tomcat 4 on Java 1.6 with these parameters successfully for some time, but some may have been introduced to help garbage collection on Java 1.4 which was the basis of our Tomcat 4 install for a long time, and may now doing more harm than good). Some notes: Application memory footprint is around 1GB, probably slightly over. CPU is not an issue - all machines serving the app (load balanced) are < 30% CPU Lots of headroom on physical memory on the machines. -XX:MaxPermSize=512m was the only parameter added as part of the 5.5 upgrade and was reactive to an outofmemory permgen space issue (which it solved). Running on Java 1.6, Solaris OS -server -Xms1280m -Xmx1280m -XX:MaxPermSize=512m -XX:ParallelGCThreads=20 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:SurvivorRatio=8 -XX:TargetSurvivorRatio=75 -XX:MaxTenuringThreshold=0 -XX:+AggressiveOpts -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:-TraceClassUnloading -Dsun.io.useCanonCaches=false -Dsun.net.client.defaultConnectTimeout=60000 -Dsun.net.client.defaultReadTimeout=60000

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