We have very rare problems on our Drupal-based portal (few times per month, mostly under havy load).
Problem symptoms are:
- Number of apache processes spikes to maximum.
- Number of connections to MySQL spikes to # of Apache processes.
- There are no spikes on MySQL qps graph.
- Project in not working, but apache restart solves problem.
- There is no unreal CPU load on backend.
- Before apache restart there is no queries in MySQL (we do “show processlist” before restart).
- Does empty mysql process list mean that problem is probably on backend?
- What steps can we perform to search for performance problems on backend (we can’t do profiling with xdebug on heavy site waiting problem for weeks)? One such rare problem with similar symptoms we found (connecting from our code to slow and unreliable external service).
Thanks in advance.