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Debugging with user trace
Message flow nodes write messages to user trace when they are processing work. You can use these messages offline to review the activity in a message flow and show information such as which nodes were invoked, what code they ran, and through which terminals the messages was sent.
Before you start to trace a broker, or any of its execution groups or messages flows, the broker must be running, and you must have deployed the message flows by using the WebSphere® Message Broker Toolkit.
If an error occurs while a message is being processed, the exception is written to user trace. If the error is not caught in the message flow, it is also be written to the system log. Each entry in user trace is prefixed by "BIP". You can search for BIP messages in the information center. For information about the location of user trace log files on different operating systems, see User trace.
When you start user tracing, you cause additional processing for every activity in the component that you are tracing. Large quantities of data are generated by the components. Expect to see some effect on performance while trace is active. You can limit this additional processing by being selective about what you trace, and by restricting the time during which trace is active.
- Trace is inactive by default. Turn it on by following the instructions in Starting user trace.
- If you need to check what tracing options are currently active for your brokers, use the mqsireporttrace command, as described in Checking user trace options.
- To change user trace options, use the mqsichangetrace command, as described in Changing user trace options.
- To retrieve user trace, use the mqsireadlog command, as described in Retrieving user trace.
- To format the information that is generated by the mqsireadlog command, use the mqsiformatlog command, as described in Formatting trace.
- For information about how to interpret the contents of user trace, see Interpreting trace.
- To stop user trace, use the mqsichangetrace command, as described in Stopping user trace.
- To clear old information from trace files, use the mqsichangetrace command, as described in Clearing old information from trace files.
- Alternatively, you can include a Trace node in your message flows when you design them. Use a Trace node when you want to specify an alternative location for the trace contents. For more details, see Debugging by adding Trace nodes to a message flow.