Dear all,

Getting the JVM size too big can cause as many problems as having it too
small: It has to be right sized.  The application owner has to determine
the correct size for the dataset, which in the case of the Midtier,
involves using some load testing tools and optimising the cache for the
way in which the product is being used.

In terms of setting JVM flags, ms and mx should be reasonable close to
each other – ideally equal for an application server – the application
server is managing object within the JVM.  If you have large difference
and ms is too small, every time the heap has to be grown into the gap you
will suffer a performance penalty. If you need a heap of a certain size
then that should be given to the JVM when it starts up – so growing the
heap is a rare event.

I normally advise to set mx to be 10% more than ms or 128MB whichever is
less – that allows for the situation where an unexpected situation arises
and a little more heap is needed. Monitoring if the "head room" is ever
used, will also warn for memory leaks or that you’ve not go your heap
quite big enough to cope with the normal working set size.


John Baker

-- 
Java System Solutions - home of the SSO Plugin for the AR System
http://www.javasystemsolutions.com

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