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JVM Heap size - How

 
Ramu Nur
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Hi
Is there a standard technique to set the JVM heap size for an application? Or is it a trail-and-error (after profiling) with some start up values?

Thanks
 
Deepak Bala
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Trail and error mostly. Some apps hog memory and others dont. It depends on how state is maintained; what is cached; how large the cache is; what the purge policy for caches are; etc etc.

A load and performance test usually highlights the limits of CPU / memory / Threads. A good rule of thumb is to add some buffer to the max limit (say 20%. But 20% of what number ? That can be a factor too).
 
chander shivdasani
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Ya, i agree to Deepak. Its mainly by trial error.
One thing to look is how often does JVM do GC. Make sure its not spending most of its time doing GC.
 
It is sorta covered in the JavaRanch Style Guide.
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