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From AJ ...@dude.podzone.net>
Subject Re: Is LOCAL_QUORUM as strong as QUORUM?
Date Thu, 23 Jun 2011 00:50:37 GMT
On 6/22/2011 5:56 PM, mcasandra wrote:
> LOCAL_QUORUM gurantees consistency in the local data center only. Other
> replica nodes in the same DC and other DC not part of the QUORUM will be
> eventually consistent. If you want to ensure consistency accross DCs you can
> use EACH_QUORUM but keep in mind the latency involved assuming DCs are not
> located within short distance.
>
> --
> View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Is-LOCAL-QUORUM-as-strong-as-QUORUM-tp6506592p6506621.html
> Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com.
>

Thanks mcasandra.

I would like to know the minimal consistency_level to assure absolute 
consistency with a multiple data center setup for minimal latency.  Just 
as quorum read/writes is the minimal needed to assure consistency with a 
single data center cluster, what is the equivalent read/write 
consistency_level value pair with a multi data center environment?

I'm thinking... writes at EACH_QUORUM and reads at LOCAL_QUORUM?  This 
will handle when a data center gets partitioned.   The write will fail 
if the dc's get partitioned.  If the partition happens after a 
successful write, then that's ok and a local quorum is all that's needed 
for a subsequent read that's consistent.

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