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From Selva Kumar <wwgse...@yahoo.com>
Subject Multi data center configuration - A question on read correction
Date Wed, 15 Jun 2011 01:44:00 GMT
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 
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