Thursday, November 15, 2007

About JVM Heap Size

Garbage collection is the VM process of de-allocating unused Java objects in the Java heap.The Java heap is where the objects of a Java program live. It is a repository for live objects, dead objects, and free memory. When an object can no longer be reached from any pointer in the running program, the object is garbage.

The JVM heap size determines how often and how long the VM spends collecting garbage. An acceptable rate for garbage collection is application-specific and should be adjusted after analyzing the actual time and frequency of garbage collections.

If you set a large heap size, full garbage collection is slower, but it occurs less frequently. If you set your heap size in accordance with your memory needs, full garbage collection is faster, but occurs more frequently.p>

The goal of tuning your heap size is to minimize the time that you spend doing garbage collection while maximizing the number of clients that you can handle at a given time.

To ensure maximum performance during benchmarking, you might set high heap size values to ensure that garbage collection does not occur during the entire run of the benchmark.

You might see the following java error if you are running out of heap space:

java.lang.OutOfMemoryError 
java.lang.OutOfMemoryError Exception in thread "main"
About Generational GC
JVM heap size
Heap Size
Heap Size Options
Heap Size
OutOfMemoryExeception

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