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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-10726) Read repair inserts should not be blocking
Date Sat, 05 Mar 2016 00:41:40 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15181364#comment-15181364
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Jonathan Ellis edited comment on CASSANDRA-10726 at 3/5/16 12:40 AM:
---------------------------------------------------------------------

Yes.  And if two of the nodes agree on the most recent value then we don't need to block on
the third being updated since our monotonicity of future quorum reads is already assured.


was (Author: jbellis):
Yes.  And if two of the nodes agree on the most recent value then we don't need to block on
the third being updated.

> 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out of date replicas is blocking.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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