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From Aaron Morton <aa...@thelastpickle.com>
Subject Re: Understand eventually consistent
Date Fri, 18 Feb 2011 01:26:37 GMT
For background...

http://wiki.apache.org/cassandra/ArchitectureOverview
(There is a section on consistency in there)

For  deep background...
http://www.allthingsdistributed.com/2008/12/eventually_consistenthtml
http://s3.amazonaws.com/AllThingsDistributed/sosp/amazon-dynamo-sosp2007.pdf

In short, yes (for all your questions) if you read and write at Quorum you have consistency behavior
for your operations. Even though some nodes 
may have an inconsistent view of the data, e.g. one node is partitioned by a broken network
or is overloaded and does not respond. 

Aaron

On 18 Feb, 2011,at 02:11 PM, mcasandra <mohitanchlia@gmail.com> wrote:


Why is Cassandra called eventually consistent data store? Wouldn't it be
consistent if QUORAM is used?

Another question is when I specify replication factor of 3 and write with
factor of 2 and read with factor of 2 then what happens?

1. When write occurs cassandra will return to the client only when the
writes go to commit log on 2 nodes successfully?

2. When read happens cassandra will return only when it is able to read from
2 nodes and determine that it has consistent copy?
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