The initial Java™ heap size should not be set equal to the maximum Java heap size

Technote (FAQ)
Problem
Setting the initial Java heap size too high can result in inefficient garbage collection and heap compaction. This is because by the time garbage collection is performed, the heap is very large and is probably fragmented. Therefore, the Application Server Xms setting should not be set equal to the Xmx setting.
Cause
Inefficient garbage collection.
Solution
Setting the initial Java heap minimum equal to the Java heap maximum is not recommended. Doing so can delay the start of garbage collection until the heap is full. Therefore, the first time the Garbage Collector runs is a very expensive operation.

The heap is also likely to be very fragmented by the time heap compaction is required. This is also a very expensive operation.

IBM recommends that you start your application with the minimum heap size needed. When it starts up, the Garbage Collector will run often and, because the heap is small, it runs efficiently.
Related information
IBM® Developer Kit and Runtime Environment Java™ 2 Tech












Document Information

Product categories: Software, Application Servers, Distributed Application & Web Servers, WebSphere Application Server, Java SDK
Operating system(s): Multi-Platform
Software version: 3.5, 4.0, 5.0, 5.1, 6.0
Reference #: 1160795
IBM Group: Software Group
Modified date: 2004-04-14