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From William Oberman <>
Subject advice for EC2 deployment
Date Thu, 21 Apr 2011 15:28:17 GMT

My service is not yet ready to be fully multi-DC, due to how some of my
legacy MySQL stuff works.  But, I wanted to get cassandra going ASAP and
work towards multi-DC.  I have two main cassandra use cases: one where I can
handle eventual consistency (and all of the writes/reads are currently ONE),
and one where I can't (writes/reads are currently QUORUM).  My test cluster
is currently 4 smalls all in us-east with RF=3 (more to prove I can
clustering, than to have an exact production replica).  All of my unit
tests, and "load tests" (again, not to prove true max load, but to more to
tease out concurrency issues) are passing now.

For production, I was thinking of doing:
-4 cassandra larges in us-east (where I am now), once in each AZ
-1 cassandra large in us-west (where I have nothing)
For now, my data can fit into a single large's 2 disk ephemeral using RAID0,
and I was then thinking of doing a RF=3 with us-east=2 and us-west=1.  If I
do eventual consistency at ONE, and consistency at LOCAL_QUORUM, I was
-eventual consistency ops would be really fast
-consistent ops would be pretty fast (what does LOCAL_QUORUM do in this
case?  return after 1 or 2 us-east nodes ack?)
-us-west would contain a complete copy of my data, so it's a good eventually
consistent "close to real time" backup  (assuming it can keep up over long
periods of time, but I think it should)
-eventually, when I'm ready to roll out in us-west I'll be able to change
the replication settings and that server in us-west could help seed new
cassandra instances faster than the ones in us-east

Or am I missing something really fundamental about how cassandra works
making this a terrible plan?  I should have plenty of time to get my
multi-DC working before the instance in us-west fills up (but even then, I
should be able to add instances over there to stall fairly trivially,



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