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From Javier Canillas <javier.canil...@gmail.com>
Subject Re: Understand eventually consistent
Date Thu, 24 Feb 2011 18:51:58 GMT
Well, it will need all nodes that are required on the operation to be up,
and to response in a timely fashion, even a time-out rpc of 1 replica will
get you a fail response.

CL is calculated based on the RF configured for the ColumnFamily.

"The ConsistencyLevel is an enum that controls both read and write behavior
based on <ReplicationFactor> in your storage-conf.xml."

QUORUM = RF / 2 +1;
ALL = RF
ONE = 1
ANY = 0

Then, on a column family configured with RF = 6, QUORUM means "be sure to
write at least over 4 nodes before responding", but on a column family
configured with RF = 3, QUORUM means "be sure to write on 2 at least". In
cases where RF is 1 or 2, then QUORUM is like ALL ("be sure to write on all
nodes involved").


On Thu, Feb 24, 2011 at 3:29 PM, mcasandra <mohitanchlia@gmail.com> wrote:

>
>
> Javier Canillas wrote:
> >
> > 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.
> >
>
> I am assuming even read will succeed when CL QUORUM and RF=3 and 1 node is
> down.
>
>
> Javier Canillas wrote:
> >
> > Now consider same OP but with CL ALL, it will fail since it cant
> > assure that coordinador and both replicas are updated.
> >
>
> Can you please explain this little more? I thought CL ALL will fail because
> it needs all the nodes to be up.
> http://wiki.apache.org/cassandra/API
>
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