IBM BPM, V8.0.1, All platforms > Tuning > Advanced tuning > Advanced Java heap tuning

Monitoring garbage collection

To set the heap correctly, first determine how the heap is being used. You can do this by collecting a verbosegc trace, which prints garbage collection actions and statistics to stderr.

You can use the administrative console to activate the verbosegc trace.

1. In the administrative console, click Servers > Server Types > WebSphere application servers > server_name.
2. In the Server Infrastructure section, click Java and process management > Process definition > Java virtual machine.
3. In the Server Infrastructure section, click Java and process management > Process definition, select either Control or Servant, and then select Java virtual machine.

4. Select the Verbose garbage collection check box.

Sample verbosegc GC trace output at startup

<?xml version="1.0" ?>
<verbosegc version="20100216_AA_CMPRSS">
<initialized>
   <attribute name="gcPolicy" value="-Xgcpolicy:gencon" />
   <attribute name="maxHeapSize" value="0x80000000" />
   <attribute name="initialHeapSize" value="0x80000000" />
   <attribute name="compressedRefs" value="true" />
   <attribute name="compressedRefsDisplacement" value="0x0" />
   <attribute name="compressedRefsShift" value="0x0" />
   <attribute name="pageSize" value="0x1000" />
   <attribute name="requestedPageSize" value="0x1000" />
</initialized>

You can parse the verbosegc output using a text editor, or a visualization tool, for example, the IBM Pattern Modeling and Analysis Tool (PMAT) for Java Garbage Collector.

You can download this tool from IBM alphaWorks.

For a detailed description about IBM Java garbage collection algorithms, see the Garbage Collectors section in the Understanding the IBM JDK for Java chapter of the IBM Java 6 Diagnostics Guide.

Advanced Java heap tuning