In-Memory Performance

Ryan Zezeski rzezeski at basho.com
Thu Aug 4 10:23:48 EDT 2011


On Wed, Aug 3, 2011 at 4:54 PM, Les Mikesell <lesmikesell at gmail.com> wrote:

>
> Are you confusing membase with memcache?  The former is a persistent,
> replicated store, or at least that is the claim; the latter a cache.
> http://www.couchbase.org/wiki/**display/membase/Membase+**Architecture<http://www.couchbase.org/wiki/display/membase/Membase+Architecture>
>
> --
>  Les Mikesell
>   lesmikesell at gmail.com
>
>
>
Les,

You are right, I was thinking of memcached when I wrote that reply.
 However, I don't know if that changes much of what I said.  Looking at
membase docs [1,2] it is essentially a drop-in (they use the term "OTC" for
Over The Counter) replacement for shops traditional memcached deployments
but adds persistence, replication, etc (although, I thought I remember there
being two different kinds of buckets in membase, one that is persisted and
one that is not, what's the default?).  Looking at the vbucket literature it
sounds to me as if replication is something you decide to add, not on by
default [2].  Furthermore, it's a master/slave replication strategy which is
different from Riak's quorums.  For example, when doing a read against Riak
with N=3 it will _always_ contact 3 vnodes even if you set R=1 (it just
won't wait for all 3 replies).  Contrast that with membase which will only
perform a read from the master which will be less expensive because you
don't have to perform coordination on the replies.  For a membase deployment
to kinda look like a Riak one it should have 2 replicas using a one-to-many
strategy (as well as being persisted to disk).  I'd be interested to see how
the two would compare but now I'm drifting off topic a bit.

-Ryan

[1]: http://www.couchbase.org/wiki/display/membase/vBuckets

[2]: http://dustin.github.com/2010/06/29/memcached-vbuckets.html
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