Close unused persistent memcached connections after specified timeout.

[arjenschol]

Persistent connections to memcached appear to be only closed when apache/php-fpm
is restarted.

Our persistent identifier is based on the application version, so old data for
some caches is automagically expired. However, the old persistent connections
won't be closed and keeps lots of unused tcp connections open.

Test script:

[mkoppanen]

Hmm, I wonder if it would be just easier to reload apache / php-fpm during deployment? I'll take a look at the timeout option

[sodabrew]

libmemcached handles the underlying connections for us, and there are no options for terminating connections to idle backend servers: http://docs.libmemcached.org/memcached_behavior.html