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https://issues.apache.org/jira/browse/CASSANDRA-10726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16126376#comment-16126376
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Xiaolong Jiang commented on CASSANDRA-10726:
--------------------------------------------
[~krummas] After digging into this, I think the problem is there are two pathes
to do the read repair. The first path is the one I fixed which is directly part
of read call. The other path is back ground AsyncReadRepair runner which use
same DataReslover to resolve the conflict. Since they are using same
DataReslover to reslove, they are sharing same repairResponseRequestMap object.
So the background AsyncRepairRunner is also changing this map causing the
interation on the repairResponseRequestMap keySet get CME. Let me see how I can
fix this.
> 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
> Assignee: Xiaolong Jiang
> Fix For: 4.x
>
>
> 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 to update out of date replicas is blocking.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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