Transaction traces are collected when the response time for particular transaction is too slow.
The threshold for this can be configured in the Config File by setting the traceThreshold property (defaults to 1s).
Stack trace
Transaction traces will show the methods instrumented by the DripStat Agent.
If a particular method crosses the stackTraceThreshold (defaults to 500ms), you will see a button next to it that allows you to see the full stack trace.