Server hangs when using auto_expire

[mapcentia]

We're running a MapServer/MapCache installation with about 3.000 layers and million of tile requests per day. The setup is MapCentia GC2, which have a Docker container for MapServer and one for MapCache. Each using Apache2. Cache type is disk.

The setup was running smothly, until one day the whole server starts to hang every 5 minuts or so when the server was busy. The hangs lasted for up to 30 seconds. The server ressources seemed OK and we couldn't find anything in the logs. We also couldn't provoke the hangs using Apache ab testing tool. The hangs occured only during real usage in the day time.

Recently we defaulted "auto_expire" to 3600 seconds on all layers and that seemed to cause the hangs. After removing auto_expire from the MapCache file the server is running smoothly again.