In addition to inspecting service debug logs, some advanced troubleshooting options are provided below. These are generally very low-level and are not normally required.

Thread Dumps and Profiling

If you send a SIGUSR2 to one of the daemon processes, it will dump a stack trace for each running thread into its debug log. It is written under the log bucket zuul.stack_dump. This is useful for tracking down deadlock or otherwise slow threads:

sudo kill -USR2 `cat /var/run/zuul/`
view /var/log/zuul/executor-debug.log +/zuul.stack_dump

When yappi (Yet Another Python Profiler) is available, additional functions’ and threads’ stats are emitted as well. The first SIGUSR2 will enable yappi, on the second SIGUSR2 it dumps the information collected, resets all yappi state and stops profiling. This is to minimize the impact of yappi on a running system.