unable to detect when memcached isn't running

Migrated issue, originally created by David Kavanagh ()

I've configured dogpile.cache to use memcached and the python-memcached package. I need to be able to detect when there is a failure to communicate to the memcached server. In python-memcached'd memcached.py file, the _set(..) method around line 814, a 0 is returned if the server is down. The set method returns a non-zero value on success. In the dogpile.cache.backends.memcached.py file around line 159, the set(..) method does nothing with the return value, as does the dogpile.cache.region.py file in the set(..) method. That makes it impossible to know and deal with a memcached set failure. I'd be happy to submit a patch, but wanted some feedback first. Perhaps raising a DogpileCacheException from the backend would be better.

Start with dogpile.cache.backends.memcached.py around the set method and dogpile.cache.region.py around set, then compare their behavior with python-memcached's _set method. Determine how a failed communication should be surfaced without changing successful writes, and verify that callers can distinguish a failed set from a successful one.