Hi, >> I'me sure this one has been done to death but does anyone have any >> guidelines on the settings of -Xms and -Xmx ($CATLINA_OPTS), or how to >> derive the optimal setting for these ?
Yes, it has been asked many times. That's because everyone seems to think there's a magical guideline somewhere. There isn't. To get the best performance for your application, you have to profile your application. -Xmx is the key setting, you should start with tuning that. As long as you keep getting OutOfMemory errors, you need to increase -Xmx. You need to give yourself enough memory for peak traffic, and then some for safety and overhead. So run your app again and again with a load test tool, see how much traffic you can handle and how much memory it requires. Once you've found the proper value for -Xmx, think about -Xms, the minimum size. Setting this close to -Xmx will speed up your server startup if you cache a lot stuff on startup. However, if your normal usage pattern requires very little memory, and only peak times require high memory, you can keep this low to avoid taking up memory unnecessarily. Keep -verbose:gc on so that you can see what garbage collection is doing. If you have a big heap, GC may take more time, and may create visible pauses to your users. Experiment with the various GC algorithms (-Xincgc etc.) to see if they work well. By that point you should be a bit more familiar with and comfortable with more advanced tuning. Analyze your app to get an estimate of the breakdown between the young and old GC generations. Tuning -XX:NewSize and -XX:MaxNewSize can help a *lot*. Good luck, Yoav Shapira Millennium ChemInformatics
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