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We have 2 Datacenters each having 3 nodes with replication factor of 3 for each Datacenter (Total 6 replicas) with read consistency level as LOCAL_ONE. Since we are not using LOCAL_QUORUM or DC_LOCAL_QUORUM, is it acceptable to go with 3 nodes in each datacenter?

Can anyone suggest the best Consistency level for read operation with the current configuration in order to get the latest information across the datacenters?

Configuration:
Solr DC1 : 3 nodes, RF=3
Solr DC2 : 3 nodes, RF=3
Versions:
dse 4.8.3
cassandra 2.1.11

Thanks

Arun
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1 Answers1

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Having three nodes per datacemter and RF=3 in each is not unreasonable - it allows you to have durability and HA in either/both datacenters.

The consistency level will depend on your business requirements - do you need strong consistency? What should happen if the datacenters cannot communicate? Your consistency and availability requirements should dictate your consistency level.

Jeff Jirsa
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  • Thanks. Yes, we want the data to be consistent across the datacenters and need strong consistency. It's sure that we will get stale data when queried for read operation with Consistency Level - ONE or LOCAL_ONE. Can you give me your feedback on this? – Arun Jan 29 '16 at 14:51
  • In that case, you'll want to make sure you use EACH_QUORUM on writes. Doing so will allow you to read with LOCAL_QUORUM on reads (lowering your latency costs there). Alternatively, you could read with QUORUM (which would require a DC round trip), but that doesn't gain much in theory. – Jeff Jirsa Jan 29 '16 at 17:03