Some sources say it might be a good idea to disable heuristics altogether and just use generation occupancy to start a CMS collection cycle. GC might kick in too late with default settings (causing full-Gcs). Normally the GC will use heuristics to know when it’s time to clear memory. The option CMSParallelRemarkEnabled means the remarking is done in parallel to program execution – which is what you want if your server has many cores (and most servers do). I’ve read many articles and came to the conclusion that this GC is still the best one for server workloads. This option makes the JVM use the ConcurrentMarkSweepGC – It can do much work in parallel to program execution but in some circumstances a „full GC“ with a „STW pause“ might still occur. If your application generates lots of dynamic classes, this is what you want.
Glassfish java 8 code#
XX:+CMSClassUnloadingEnabledĪdditionally, you might want to allow the JVM to unload classes which are held in memory but no code is pointing to them any more. Upon next restart of the application set the limit to e.g. I suggest: Let your application run for a couple of days to get a feeling for how much Metaspace Size it uses normally. Just in case something goes wrong with the application, the JVM will not hog all the memory of the server.
The default size will be unlimited – I tend to limit MaxMetaspaceSize with a somewhat high value. This memory is used, in addition to the heap memory we specified before, for storing class meta data information. Java 8 has no „Permanent Generation“ (PermGen) anymore but requires additional „Metaspace“ memory instead. I’ve applications running with 16GB heap sizes without an issue.ĭepending on your application, you will have to try out how much memory will be best suited for your use case. For servers, both params should have the same value to avoid heap resizing during runtime. The „-Xmx/-Xms“ settings specify the maximum and minimum values for the JVM heap memory. The JVM will collect more data about the Java byte code during program execution and generate the most efficient machine code via JIT. This setting generally optimizes the JVM for long running server applications instead of startup time. Use „-server“: All 64-bit JVMs use the server VM as default anyway. Links containing more information about JVM optimization can be found here: I often wondered – what are the best „default“ JVM settings for a server application to start with in production? I read a lot on the web and tried several things myself and wanted to share what I found out, so far. I run several Java enterprise server applications. If you have any questions, you can read those links below for more information or just ask in the comments section. In this video I explain some 21 JVM parameters which are suited for most server applications.
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