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From Stu Hood <stuh...@gmail.com>
Subject Re: Understand eventually consistent
Date Fri, 18 Feb 2011 06:00:09 GMT
But, the reason that it isn't safe to say that we are a strongly consistent
store is that if 2 of your 3 replicas were to die and come back with no
data, QUORUM might return the wrong result.

A requirement of a strongly consistent store is that replicas cannot begin
answering queries until they are consistent: this is not a requirement in
Cassandra, althought arguably should be an option at some point in the
distant future.

On Thu, Feb 17, 2011 at 5:26 PM, Aaron Morton <aaron@thelastpickle.com>wrote:

> 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_consistent.html
>
> 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?
> --
> View this message in context:
> http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Understand-eventually-consistent-tp6038330p6038330.html
> Sent from the cassandra-user@incubator.apache.org mailing list archive at
> Nabble.com.
>
>

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