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Posted to user@cassandra.apache.org by vd <vi...@gmail.com> on 2010/05/12 15:15:25 UTC

what is DCQUORUM

Hi

I have read about QUORUM but lately came across DCQUORUM. What is it  and
whats the difference between the two ?

Re: what is DCQUORUM

Posted by vd <vi...@gmail.com>.

Thanks Eben


On Wed, May 12, 2010 at 7:33 PM, Eben Hewitt <eb...@gmail.com> wrote:

> QUORUM is a high consistency level. It refers to the number of nodes that
> have to acknowledge read or write operations in order to be assured that
> Cassandra is in a consistent state. It uses <ReplicationFactor> / 2 + 1.
>
> DCQUORUM means "Data Center Quorum", and balances consistency with
> performance. It puts multiple replicas in each Data Center so operations can
> prefer replicas in the same DC for lower latency.
>
> See https://issues.apache.org/jira/browse/CASSANDRA-492 for a little
> discussion.
>
> Also see
> http://svn.apache.org/repos/asf/cassandra/trunk/src/java/org/apache/cassandra/locator/DatacenterShardStrategy.java
>  and
>
> http://svn.apache.org/repos/asf/cassandra/trunk/src/java/org/apache/cassandra/service/DatacenterWriteResponseHandler.java
>
> Eben
>
>
>
> On Wed, May 12, 2010 at 6:15 AM, vd <vi...@gmail.com> wrote:
>
>> Hi
>>
>> I have read about QUORUM but lately came across DCQUORUM. What is it  and
>> whats the difference between the two ?
>>
>>
>
>
> --
> "In science there are no 'depths'; there is surface everywhere."
> --Rudolph Carnap
>

Re: what is DCQUORUM

Posted by Eben Hewitt <eb...@gmail.com>.

QUORUM is a high consistency level. It refers to the number of nodes that
have to acknowledge read or write operations in order to be assured that
Cassandra is in a consistent state. It uses <ReplicationFactor> / 2 + 1.

DCQUORUM means "Data Center Quorum", and balances consistency with
performance. It puts multiple replicas in each Data Center so operations can
prefer replicas in the same DC for lower latency.

See https://issues.apache.org/jira/browse/CASSANDRA-492 for a little
discussion.

Also see
http://svn.apache.org/repos/asf/cassandra/trunk/src/java/org/apache/cassandra/locator/DatacenterShardStrategy.java
 and
http://svn.apache.org/repos/asf/cassandra/trunk/src/java/org/apache/cassandra/service/DatacenterWriteResponseHandler.java

Eben

On Wed, May 12, 2010 at 6:15 AM, vd <vi...@gmail.com> wrote:

> Hi
>
> I have read about QUORUM but lately came across DCQUORUM. What is it  and
> whats the difference between the two ?
>
>

-- 
"In science there are no 'depths'; there is surface everywhere."
--Rudolph Carnap