About CAP theorem and Riak way of thinking

Sean Cribbs sean at basho.com
Fri Oct 8 08:18:42 EDT 2010


I think the way we've said that in the past has been a little misleading. What we meant was you can adjust the strictness of your consistency. At it's heart, Riak is an AP-style of system, meaning that given a partition, we sacrifice consistency first.  However, we look at consistency as a spectrum, not as an all-or-nothing proposition; you can choose what degree of agreement between replicas satisfies a consistent read or write. Behind the scenes, Riak will converge on a consistent value over time.

Sean Cribbs <sean at basho.com>
Developer Advocate
Basho Technologies, Inc.
http://basho.com/

On Oct 8, 2010, at 5:26 AM, Germain Maurice wrote:

> Hi everybody,
> 
> Not really a technical question, i'm thinking about CAP theorem and the Riak way of thinking.
> 
> CAP theorem says : "You can't get Consistency, Availability and Partition tolerance at the same time"
> 
> It's advised to pick two of them and don't try to satisfy the three.
> Riak says "Pick two at each operation".
> 
> So, am i right if i say : "the N_val of bucket is for Partition Tolerance, small R/W quorums are for Availability and high R/W/DW quorums are for Consistency" ?
> I think high W/DW quorums will ensure effectiveness of Partition Tolerance of the read requests in the future.
> When reading, if we have high R quorums the Partition Tolerance is lower.
> 
> I tried to list each configuration on each operation, could you correct it where i am wrong .
> N=3, R=1 :: A,P
> N=3, R=3 :: C
> N=1, R=1 :: A
> N=3, W=3 :: C
> N=3, W=1 :: A,P
> N=1, W=1 :: A
> 
> Thanks
> 
> -- 
> Germain Maurice
> Administrateur Système/Réseau
> Tel : +33.(0)1.42.43.54.33
> 
> http://www.linkfluence.net
> 
> 
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