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From Javier Canillas <javier.canil...@gmail.com>
Subject Re: Understand eventually consistent
Date Thu, 24 Feb 2011 12:27:50 GMT
First of all, in your example W=CL?

If it so, then the success of any read / write operarion will be
determine by if the CL required can be satisfied in that moment.

If you write with CL ONE over a CF with RF 3 when 1 node of the
replicas is down, then the operarion will success and HitedHandOff
will manage to propagate the op through the falling node when it comes
up.

Instead, when you execute the same OP using CL QUORUM, then it means
RF /2+1, it will try to write on the coordinator node and replica.
Considering only 1 replica is down, the OP will success too.

Now consider same OP but with CL ALL, it will fail since it cant
assure that coordinador and both replicas are updated.

Hope you can understand the relation between CL and RF

Enviado desde mi iPhone

El 23/02/2011, a las 21:43, mcasandra <mohitanchlia@gmail.com> escribió:

>
> I am reading this again http://wiki.apache.org/cassandra/HintedHandoff and
> got little confused. This is my understanding about how HH should work based
> on what I read in Dynamo Paper:
>
> 1) Say node A, B, C, D, E are in the cluster in a ring (in that order).
> 2) For a given key K RF=3.
> 3) Node B holds theyhash of that key K. Which means when K is written it
> will be written to B (owner of the hash) + C + D since RF = 3
> 4) If Node D goes down and there is a write again to key K then this time
> key K row will be written with W=1 to B (owner) + C + E (HH) since RF=3
> needs to be satisfied. Is this correct?
> 5) In above scenario where node D is down and if we are reading at W=2 and
> R=2 would it fail even though original nodes B + C are up? Here I am
> thinking W=2 and R=2 means that 2 nodes that hold the key K are up so it
> satisfies the CL and thus writes and read will not fail.
> --
> View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Understand-eventually-consistent-tp6038330p6058576.html
> Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com.

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