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 david clark (DPCLARK12)
Cox Communications
Sr. Manager Platform Operations
Cox Communications
US
DPCLARK12 Member since 2012 44 posts
Cox Communications
Posted: July 31, 2017
Last activity: August 11, 2017
Posted: 31 Jul 2017 15:45 EDT
Last activity: 11 Aug 2017 10:45 EDT
Closed

DNode RF settings for clusters of 6 nodes

All,

We currently use the default RF of 3 for Cassandra for the data keyspace in a 6 node cluster. Has any played with changing this value in larger clusters?

***Updated by moderator: Lochan to add SR Exists group tag***

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Posted: 4 years ago
Posted: 11 Aug 2017 10:37 EDT
Xavier Merlin (MERLX)
PEGA
Principal Software Solutions Engineer
PEG
GB

I didn't and I wouldn't.


If you increase the replication factor, then more nodes need to be contacted when you do a "write" for instance. So it is going to be chattier in the network.  There would be more "write" overall in the cluster so the cluster will be slower. You also lose in terms of space. You only win in terms of availability.


For instance we a consistency level set to 1 and a RF of 5, the data will still be available in 1 node even if 4 are failing.


If you decrease the replication factor then the opposite happens. 


RF of 3 appears to be the right middle ground.

We'd prefer it if you saw us at our best.

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