Admin: Memory
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Memory Pools
Java organizes its memory into pools, depending on the memory use. The main long-term heap memory is the Tenured memory. Other memory are optimizations of the Tenured memory. Eden is new, short-term memory. Survivor is long-lived memory.
CodeCache
The CodeCache is the JVM's non-heap memory pool containing the JNI compiled Java class code.
Eden
The Eden memory pool is used by the JVM for new, short-lived memory. Free memory in the Eden can be collected in fast garbage collections.
The Eden memory size is configured with -Xmn128m. In general, the JVM's defaults are fine.
PermGen
The PermGen pool is an important memory heap pool used for classes and other permanent memory. If an application has a lot of classes, it's possible for this memory to be used up.
For restarts, the PermGen can have important memory leaks, where a restarted WebApp might not release its classes and the PermGen memory can increase. The PermGen leaks tend to be application or framework errors where a class is either stored in an incorrect environment, like saving a servlet class in a ThreadLocal or in a system object.
