EACH_QUORUM With List Of DataCenters

[Bharat Kondeti]

Hi,

 

I am looking for some ideas on achieving a consistency of EACH_QUORUM on a 3 datacenter scenario, with a tolerance for 1 data center loss for writes.

 

Based on my understanding, EACH_QUORUM does not tolerate a data center loss. All my writes will fail as long as the data center is down. One option, is to retry the request with lower consistency level like 'QUORUM'.

 

Assuming that my client application knows that a datacenter is down, is there a way from Cassandra client driver to pass in a list of live/up datacenters, so the coordinator node tries to achieve EACH_QUORUM only on those datacenters.

 

Would appreciate any insight on this.

 

Thanks

Bharat

[Alexandre Dutra]

Hello Bharat,

EACH_QUORUM is a very strong consistency level that does not tolerate datacenter failures. Furthermore, you cannot tell the coordinator to "ignore" a specified datacenter when trying to achieve EACH_QUORUM. There are actually few use cases that really require such a strong commitment.

Lowering your consistency requirements to QUORUM or LOCAL_QUORUM might be a reasonable choice; you might also want to have a look at DowngradingConsistencyRetryPolicy and the discussion around JAVA-1005.

Regards,

Alexandre

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Alexandre Dutra

Driver & Tools Engineer @ DataStax