Transparent failover and restore?

[Brad Fitzpatrick]

On Sat, 18 Dec 2004, Jon Valvatne wrote:

> I think the point is this: If you're using memcached in a way that means
> losing a server will bring down the system, then you should probably be
> looking at using the MySQL "redundant storage thing" instead of the
> memcached "cache thing". Traditional usage of a cache usually means
> losing parts or all of it is *not* fatal.

Exactly.

Or do what LiveJournal does:  have a dozen memcached machines, each with
about the same amount of cache.  So if you lose a machine, you only lose
1/12th of the cache, until it re-hashes and populates over the next 10
minutes.

I suppose I see the arguments from the people who only have 2 machines
and want good cache hit rate performance in the face of failure, but the
cache coherency problems just seem too hard to re-implement when solutions
already exist.

Perhaps memcached atop NDB cluster (what MySQL Cluster is built on)
would be interesting.  NDB would do the cache coherency across the
cluster, and memcached could simply do the protocol handling and LRU
maintenance and cache discarding...

- Brad