I'm trying to track down an issue with our installation where when the cache is cleared, there is a spike in MySQL queries/connections (around about 170 concurrent), which leaves the site inaccessible for about 5 minutes.
If I take a snapshot of the site and do this on my laptop, I have the same problem (max CPU usage until the processlist is cleared out).
This means that enabling a module means 5 minutes of downtime.
On our server we run memcache and x-cache. It is quite a powerful VM, usually with a load average below 1 (~50k impressions a day), but this rockets to over 20 when the above mentioned problem occurs.
Curiously, my laptop exhibits the same behaviour when caching is turned off. It does not have memcache/opcode cache.
Running PHP5, MySQL 5, X-Cache and Memcache.
I think the problem might be related to table locking, but can't be certain!
Any thoughts much appreciated!