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https://issues.apache.org/jira/browse/CASSANDRA-10726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16128832#comment-16128832
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Marcus Eriksson commented on CASSANDRA-10726:
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Your patch fixes the issue, but don't we actually want the different
invocations to share results? I tried replacing the HashMap with a
ConcurrentHashMap and that also fixes the issue.
I also ran a small test to make sure standard read performance is not horrible,
but it seems we are getting way more timeouts with this patch - I started a 3
node ccm cluster, inserted 1M rows with stress, flushed and stopped node3,
removed all its data and restarted, then read back 1M rows with CL=ALL. With
the patch I'm getting lots of timeouts, without it, no timeouts.
> 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 to update out of date replicas is blocking.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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