[jira] [Created] (CASSANDRA-13611) Digest mismatch in Quorum read

["Dikang Gu (JIRA)" <ji...@apache.org>]

Dikang Gu created CASSANDRA-13611:
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             Summary: Digest mismatch in Quorum read
                 Key: CASSANDRA-13611
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13611
             Project: Cassandra
          Issue Type: Improvement
          Components: Coordination
            Reporter: Dikang Gu
            Assignee: Dikang Gu


In current implementation, when we issue a quorum read, C* will send full data request to one replica, and send digest requests to other replicas. If the digest mismatch, C* will send another round of full data request to all replicas. 

In our environment, we find in P99 case, digest are always mismatch, so we are doing 2 round trips of requests in P99, which hurts our P99 latency a lot.

We propose that in quorum read case, we send full data replicas to the quorum replicas directly, reconcile them and send back to client. In our experiment , it reduced the P99 latency by 20% ~ 30%.



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