On 6/22/2011 8:20 PM, mcasandra wrote:
Well it depends on the requirements. If you use any combination of CL with
EACH_QUORUM it means you are accepting the fact that you are ok if one of
the DC is down. And in your scenario you care more about DCs being
consistent even if writes were to fail. Also you are ok with network
latency.
I think there is a broader design question here and you might be able to
solve it with LOCAL_QUORUM if you handled it at application or load
balancing layer. Is this active/active data center? What's your actual
requirements? Are these external clients that can go to any data center?
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I require 3 (or more) geographically diverse dc's serving local users.
The next arbitrary closest dc will serve as a 1-replica fail-over for
the previous dc in case it becomes unavail altogether. So, each dc is
active for it's locale and a failover for one of the others; like a
daisy chain configuration. I was imagining a series of events where the
primary dc gets updated at local_quorum, followed by that dc losing all
network connectivity before the backup gets the change. Then, the same
user gets redirected to the backup dc and does a read at local_quorum
and gets stale data.
But, I realize now if I substituted each_quorum for local_quorum for
writes, then, in the case of fail-over, the writes would fail. That's
fine for consistency's sake, but is a high price to pay. I have to
think on this more and what I want. Thanks for the help.
