WebSphere Extended Deployment, Version 6.0.x
             Operating Systems: AIX, HP-UX, Linux, Solaris, Windows, z/OS


Modifying the JVM heap size

The heap size setting directly relates to how many dynamic clusters are supported on a server. You might need to modify this setting based on your environment configuration. Modifying your heap size can affect application placement as well as health management function.

Before you begin

Before modifying heap size, read the Java memory tuning tips that are available in the WebSphere Application Server Information Center.

About this task

The total value of dynamic clusters that are supported on the machine must be less than half of the total RAM of that machine. To find the maximum heap size, use the following equation:

total RAM / 2 / number of servers = maximum heap

For example, to support three servers on a machine with 1.5 GB of RAM, each dynamic cluster must be 750 MB. Use a maximum heap size of 250 MB to support three servers on that single machine (1500 MB / 2 = / 3 servers = 250 MB). The following table contains some maximum heap size samples.

Table 1. Maximum heap size samples
WebSphere Extended Deployment Server total RAM in GB Number of supported servers Dynamic cluster size in MB Approximate maximum heap size in MB
1.5 1 Less than 750 750
1.5 2 Less than 750 375
1.5 3 Less than 750 250
2 1 Less than 1000 1000
2 2 Less than 1000 500
2 3 Less than 1000 333

The following steps outline the process for modifying the heap size on a dynamic cluster, which is a fundamental component of the WebSphere Extended Deployment dynamic capabilities.

Procedure

  1. In the administrative console click Servers > Dynamic clusters > cluster_name > Server template > Java and process management > Process definition > Java virtual machine.
  2. Modify the heap size accordingly. Typically, the total of all the dynamic clusters on a machine must be less than half of the total RAM of that machine. The default maximum heap size for a dynamic cluster is 256 MB.
  3. Click OK.



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Monitoring and tuning health management
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Last updated: Nov 30, 2007 3:59:37 PM EST
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