Regarding Memcached Server configuration?
marcus at synchromedia.co.uk
Wed Sep 26 17:57:56 UTC 2007
On 26 Sep 2007, at 18:39, Dan Christian wrote:
> I'm a bit confused about the redundancy aspects of memcached. My
> understanding is that you can have multiple memcacheds, but they store
> different objects (based on the keys).
> Tell me if I understand this right. If I run a memcached on each of 2
> machines, then the failure of a machine takes out half the cached
Yes, it's a bit like a JBOD array of disks - losing a disk will only
lose the data on that disk. From the client perspective there is
(generally) only one apparent cache.
> These values will continue to be un-cached until that
> machine is removed from the client's configuration.
> Is there an automatic recovery mechanism?
Not for the data (it's just a cache!), but for the general operation,
yes. Try searching for 'consistent hashing' in this list's archives.
> Is there a (big) performance hit when the configuration changes?
Depends on your app - the more memcache servers you have, the smaller
the hit if one dies. If you have a config change that affects all
servers, it can amount to a big hit. You can cheat a bit by 'pre-
warming' your newly configured caches. It's also relative to how much
more efficient the cache is than your app.
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