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https://issues.apache.org/jira/browse/CASSANDRA-10726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16574643#comment-16574643
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Alex Petrov commented on CASSANDRA-10726:
-----------------------------------------
It seems that there still might be a problem with {{Accumulator}} during
{{BlockingReadRepair}}.
{{DataResolver}} is created in {{BlockingReadRepair#startRepair}}, which is
gets {{allReplicas}} from {{ReadCallback#endpoints}}, which gets it through
{{AbstractReadExecutor#getReadExecutor}}, where they represent
{{consistencyLevel.filterForQuery(keyspace, allReplicas)}}.
This means that, when we're sending more data requests, we will call
{{getLiveSortedEndpoints}} and can end up with more nodes, but since
{{Accumulator}} was initialised with just "target" nodes, if we keep getting
responses (e.g. if the node was slow, not dead, which is more often the case),
{{Accumulator}} will overflow. Unfortunately, testing with RF3 won't reveal
that.
> 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: Blake Eggleston
> Priority: Major
> 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 to update out of date replicas is blocking.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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