Enabling verbose garbage collection for IBM JVM
To enable verbose garbage collection for IBM Java Virtual Machines, add the -verbose:gc flag to the JVM options. Other options exist for the same functionality.
IBM estimates that the overhead associated with verbose garbage collection is minimal and estimated to be 2% of the garbage collection time. In other words, if the JVM spends 5% of its time garbage collecting without verbose garbage collection, it would spend 5.1% of the time garbage collecting with verbose garbage collection.
The output provided is in XML format. This output is generally rich enough for a thorough analysis. In general, there is no need for additional levels of logging.
Used with WebSphere, the IBM JVM outputs garbage collection logs into a file
called native_stderr.log.
IBM provides the IBM Support Assistant. You can install multiple plugins within this tool. Several plugins are available for the IBM JVM and WebSphere. These tools provide deep analysis of JVM behavior, spot issues, and recommend how to tune the JVM.
The IBM Support Assistant Workbench
IBM provides the IBM Support Assistant Workbench. It is possible install multiple plugin tools within the workbench. The “IBM Monitoring and Diagnostic Tools for Java – Garbage Collection and Memory Visualizer” is the tool to use to analyze garbage collection logs.
The tool provides some tuning recommendations. The recommendations work more for the IBM JDK than the HotSpot JDK. Additionally, the tool provides graphs with hints on JVM behavior that help identify issues such as memory shortages or excessive pauses.