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cassandradatastaxdatastax-enterprise

Cassandra : LOCAL_QUORUM vs QUORUM, when all datacenter/servers are physically locals, on the same 10gbps network

I have two Cassandra datacenter, but all the servers are in the same building, connected with 10 gbps network.

I don't plan to have servers in another location.

The RF is 2 in each datacenter.

I need to ensure strong consistency, so I plan to use QUORUM.

Question : are there any advantages for me of using LOCAL_QUORUM instead of QUORUM ?

Thank you

Solution

  • Are there any advantages for me of using LOCAL_QUORUM instead of QUORUM?

    The most important consideration here, is that with 2 DCs with RF == 2, QUORUM and LOCAL_QUORUM equate to different values (number of replicas to be contacted).

    • LOCAL_QUORUM == 2
    • QUORUM == 3

    So the advantage I see with LOCAL_QUORUM, would be that the application would be waiting on fewer replicas. With 2 DCs and 2 replicas in each DC, operations @ LOCAL_QUORUM would wait for responses from 2 replicas.

    QUORUM operations would consider all 4 replicas across the cluster, and wait for a response from 3. So there would likely be a slight performance advantage to LOCAL_QUORUM (awaiting fewer replicas to respond).

    The downside, is that using LOCAL_QUORUM in this case wouldn't be able to tolerate a node being down. So if a single node crashed or became unresponsive, then all operations will fail until that node is resurrected.