Occasional "No servers available" error from MemCache

[jszmajda]

Hello, thanks for writing a supremely useful library!

It works most of the time, but once in a while we get a "No servers available" message from the MemCache client. I'm not sure what could cause this. We're connecting to the memcache servers just fine from Rails proper, but MegaMutex still has trouble.

We're using Passenger, so I thought it could've been an issue with forking, but I can't seem to find any correlation between forking and the error.

Any ideas?

Thanks!
-Josh

[nfelger]

Hi Josh,

The error you get comes directly from memcache-client (see Memcache#get_server_for_key at https://github.com/mperham/memcache-client/blob/master/lib/memcache.rb), and is raised when the server list is configured to be empty or none of the servers can be connected to. The fact that this only happens intermittently suggests that you are probably experiencing connection issues some of the time.

This could have a number of reasons, and as you suggested, these are also the symptoms of passenger's "smart"/"smart-lv2" spawning method, as described at http://www.productionhacks.com/2010/04/15/memcached-and-passenger-connection-sharing/. We are not using smart spawning ourselves though, so I can't be sure. Can you try running one of your instances with passenger_spawn_method set to conservative?

(Note that the patch described on the link above won't work for MegaMutex as it's not sharing connections with the various Rails caches. You could probably devise a similar solution though.)

niko