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A few months ago I discussed initial and maximum heaps sizes, feeding back to you the aggregate responses I got from you on the subject. Interestingly, in one of this month's referenced articles about tuning WebSphere Application Server (see the articles below), IBM's own performance experts state clearly that for IBM JVMs the initial and max values should be the same for optimal performance - which is also what I said in that previous newsletter based on your feedback. Bear in mind that this advice is specific to the IBM JVM, and should not be generalised to other JVMs - each is different, and even within one JVM the garbage collector used can affect the validity of this choice. The Oracle JVM did not appear to show optimal performance when initial equals max.

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The example IBM application tested showed a huge difference in performance from setting initial to max - from 8% of the time being spent in GC down to 2%. That's extraordinary. Though I always temper my response to large gains like this by remembering what my first boss said to me when I reported a 50-fold improvement in performance after a change: "wow, I didn't realise the peformance was THAT bad before!".

Now I'm going to do something I almost never do: mention a commercial tool here in the editorial section for no reason other than that it looks particularly interesting. But it is free even when used in prod, so I think it's reasonable. The tool? Nastel's new AutoPilot Heap Detective. A free tool that helps you analyse your JVM memory with no overhead except when (infrequently) used, sounds almost too good to be true - unexpected memory issues in production is one of the more painful things to happen, and the easier, quicker and earlier you can diagnose these types of problems, the better. Have a look at the tools section below if you want more details on their tool.

Now on to all our usual links to Java performance tools, news, articles and, as ever, all the extracted tips from all of this month's referenced articles.

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Jack Shirazi

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