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From "Richard Low (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-10726) Read repair inserts should not be blocking
Date Tue, 17 Nov 2015 22:25:11 GMT
Richard Low created CASSANDRA-10726:
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             Summary: Read repair inserts should not be blocking
                 Key: CASSANDRA-10726
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10726
             Project: Cassandra
          Issue Type: Improvement
          Components: Coordination
            Reporter: Richard Low


Today, if there’s a digest mismatch in a foreground read repair, the insert to update out
of date replicas is blocking. This means, if it fails, the read fails with a timeout. If a
node is dropping writes (maybe it is overloaded or the mutation stage is backed up for some
other reason), all reads to a replica set could fail. Further, replicas dropping writes get
more out of sync so will require more read repair.

The comment on the code for why the writes are blocking is:

{code}
// wait for the repair writes to be acknowledged, to minimize impact on any replica that's
// behind on writes in case the out-of-sync row is read multiple times in quick succession
{code}

but the bad side effect is that reads timeout. Either the writes should not be blocking or
we should return success for the read even if the write times out.



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