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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Multi data center configuration - A question on read correction
Date Wed, 15 Jun 2011 01:59:41 GMT
That's just read repair sending MD5s of the data for comparison.  So
net traffic is light.

You can turn off RR but the downsides can be large.  Turning it down
to say 10% can be reasonable tho.

But again, if network traffic is your concern you should be fine.

On Tue, Jun 14, 2011 at 8:44 PM, Selva Kumar <wwgselva@yahoo.com> wrote:
> I have setup a multiple data center configuration in Cassandra. My primary
> intention is to minimize the network traffic between DC1 and DC2. Want DC1
> read requests be served with out reaching DC2 nodes. After going through
> documentation, i felt following setup would do.
>
>
> Replica Placement Strategy: NetworkTopologyStrategy
> Replication Factor: 3
> strategy_options:
> DC1 : 2
> DC2 : 1
> endpoint_snitch: org.apache.cassandra.locator.PropertyFileSnitch
> Read Consistency Level: LOCAL_QUORUM
> Write Consistency Level: LOCAL_QUORUM
>
> File: cassandra-topology.properties
> # Cassandra Node IP=Data Center:Rack
> 10.10.10.149=DC1:RAC1
> 10.10.10.150=DC1:RAC1
> 10.10.10.151=DC1:RAC1
>
> 10.20.10.153=DC2:RAC1
> 10.20.10.154=DC2:RAC1
> # default for unknown nodes
> default=DC1:RAC1
>
> Question I have:
> 1. Created a java program to test. It was querying with consistency level
> LOCAL_QUORUM on a DC1 node. Read count(Through cfstats) on the DC2 node
> showed read happened there too. Is it because of read correction?. Is there
> way to avoid doing read correction in DC2 nodes, when we query DC1 nodes.
>
> Thanks
> Selva



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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