Gather verbose Garbage Collection logs | Identifying memory leaks

Analyzing verbose GC logs

To analyze memory problems in the application server, the first step is to gather GC information. You need a tool to analyze this information.

There are many tools for verbose GC log analysis, such as Tivoli Performance Viewer, Dump JVM (DMPJVM), and the WebSphere Resource Analyzer. These tools can abstract useful information, and illustrate the trend of JVM heap size usage over time.

After you analyze your native_stdout.log or native_stderr.log, you should generate charts with the following information:

• Occupancy (MB)
• Allocation rate (KBps)
• Total GC pause time (ms)
• Mark and sweep time (ms)
• Compact time (ms)
• GC cycle length and distribution (ms)
• Free space after GC (MB)
• Free space before Allocation Failure (MB)
• Size of request that caused AF (bytes)

Among these charts, some are helpful in monitoring the effects of GC and detecting many problems. You can use GC Cycle length and distribution to analyze GC frequency and distribution, Free Space after GC to analyze memory leak, and Free Space before Allocation Failure and Size of Request that caused Allocation Failure to analyze fragmentation or large objects. Other charts can also assist in the analysis.