The Java virtual machine (JVM) heap size setting directly relates to how many server instances can be started within a dynamic cluster on a specific node. You might need to modify the JVM heap size setting based on your environment configuration. The default value is 256 MB. Modifying the heap size can affect application placement and the health management function.
total_RAM / 2 / number_of_servers = maximum_heap_size
1.5 GB / 2 = 750 MB 750 MB / 3 = 250 MBThe maximum heap size is 250 MB for each server instance.
The following table contains some 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 |
When a dynamic cluster creates server instances, a server template is used to set initial values for the newly created server instance. When the application placement controller estimates the memory size of a server JVM from a cold start, it uses the maximum heap size that is defined in the server template. You can modify the JVM heap size within the server template. Newly created server instances can then use the maximum heap size you specify.