What happens when a memcached server is down and the next fetch from cache misses?

[Gerard Ottaviano]

Hi, new to memcached.  When a memcached server (#1) goes down and a subsequent fetch from cache to that server (#1) results in a miss and that results in a fetch to the backend, does that now create a new cache entry on one of the other memcached servers (#2) that is still available?  If so, when the down server (#1) becomes available again, and the next fetch of that same entry from the cache is requested, how does it determine from which server to get it, now that it exists on 2 servers?  Do we need to save the hashes which contain the server on which that cached entry exists, so we get the most recent one?  Thanks.

[Ryan McElroy]

All the logic you're describing is up to the client implementation; the servers just respond to requests they receive.

Some clients might failover a get to another memcached server; others might return an error.

Clients like mcrouter have configurable options on how to behave. Probably many other clients are configurable as well.

~Ryan (mobile)

On Dec 4, 2014, at 8:52 AM, Gerard Ottaviano <gjo...@comcast.net> wrote:

Hi, new to memcached.  When a memcached server (#1) goes down and a subsequent fetch from cache to that server (#1) results in a miss and that results in a fetch to the backend, does that now create a new cache entry on one of the other memcached servers (#2) that is still available?  If so, when the down server (#1) becomes available again, and the next fetch of that same entry from the cache is requested, how does it determine from which server to get it, now that it exists on 2 servers?  Do we need to save the hashes which contain the server on which that cached entry exists, so we get the most recent one?  Thanks.

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