What is diagnostic trace

WebSphere Application server components as well as most of the enterprise level applications use Logging framework to generate detailed trace for execution. By default this trace is disabled because it causes performance overhead but you can turn the trace on for either your application or the particular websphere component when you want to debug issue.

When you open a support request with IBM support, most of the time they will ask you to enable the trace for particular area and send the generated trace to them for further analysis of the problem.

You can turn the trace on using the WAS Admin Console GUI by going to TroubleShooting -> Logs and Trace -< Servrname. On the Logging and Tracing screen, select the Diagnostic trace.



On the Diagnostic Trace Services screen you can enable the trace by checking Enable Log checkbox.



On this screen you can also define where the output of the trace should go, you have following two options

• Memory Buffer: If you select the Memory buffer option then your messages wont be written to any file instead they will be kept in memory. But in order for you to view the messages you will have to dump the memory in file and then view it. This is not recommended option


• File: Once you decide to send the log messages to the file system it allows you to configure following properties
  
  
  
  • Maximum File Size: What should be maximum size of the trace file. Once the trace file size reaches this limit, the trace.log file would be renamed to trace+timestamp.log file and a new trace.log file would be created
  
  
  • Maximum Number of Historical Files: What is the maximum no. of historical files that should be preserved. When the trace.log reaches maximum first the WAS server would check if no. of historical files is reached if yes delete the oldest trace file.
  
  
  • File Name: Fully qualified path name where the trace file should be generated
  
  
  
  

Whatever changes you make on Configuration tab are persisted in server.xml and they require server restart for those changes to take effect. But if you want to change trace file location for running server then you can make those changes on the Runtime tab.