[jira] [Commented] (CASSANDRA-10726) Read repair inserts should not be blocking

["Nihar Dudam (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-10726?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17049547#comment-17049547 ] 

Nihar Dudam commented on CASSANDRA-10726:
-----------------------------------------

We are also very much interested in 3.11 backport. We are facing this issue very frequently in our application. 

Is there any workaround? Our application scale is increasing day by day and replicas are not up-to-date when required. I see Digest mismatch WARN almost every minute now. 

> 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: Legacy/Coordination
>            Reporter: Richard Low
>            Assignee: Blake Eggleston
>            Priority: Normal
>             Fix For: 4.0
>
>
> Today, if there’s a digest mismatch in a foreground read repair, the insert to update out of date replicas is blocking.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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