Sunday, August 2, 2009

JIT Compilation of Java code won't happen before 10000 invocations of the same code block

With the default settings of the Java 1.6 HotSpot VM running in a -server mode don't expect your java code to be compiled before 10000 invocations of same code block or the method. This may not be suitable for servers where your server load is less and might take a long time to reach 10000 invocations or where you have an environment with multiple cells and the cell gets flipped every day before reaching the threshold or the servers are getting restarted frequently. In that case you might loose the performance, where the bytecode not being compiled at all. So based on your requirements you can set a lower value of compile threshold from 10000 to get the code compiled faster and boost performance within a short period of time after the restart of the server.

Set the -XX:CompileThreshold=1500 to a lower value in the JVM option and see how your code performs and tune accordingly. Note it's not advisable to set the value below 1000 or -Xcomp (always force JIT compile) as the JVM won't even have enough profiling information before it can generate optimized code and might actually performance degradation rather than improvement. Also note running the JVM with -Xint (interpreted mode) is not advisable in production systems which severely affect the performance unless you are running in a debug code or isolating problems related to JIT.

set -XX:+PrintCompilation to see when the methods are getting complied in the jvm stdout.

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