The initial Java heap size should not be set equal to the maximum Java heap size
 Technote (troubleshooting)
 
Problem(Abstract)
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 IBM® WebSphere® Application Server Xms setting should not be set equal to the Xmx setting.
 
Cause
Inefficient garbage collection.
 
Resolving the problem
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.

But this is not a "one recommendation fits all cases" solution. Some applications might require setting the initial Java heap minimum equal to the Java heap maximum.
 
Related information
IBM developer kits: Diagnosis documentation
 
 
Cross Reference information
Segment Product Component Platform Version Edition
Application Servers Runtimes for Java Technology Java SDK
 
 


Document Information


Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server > Java SDK
Operating system(s): Windows
Software version: 6.0
Software edition:
Reference #: 1160795
IBM Group: Software Group
Modified date: Aug 30, 2005