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From "Aleksey Yeschenko (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-10726) Read repair inserts should not be blocking
Date Thu, 17 Aug 2017 12:27:00 GMT


Aleksey Yeschenko commented on CASSANDRA-10726:

bq. I wound not refactor the whole read pipeline right now I guess even though I do agree
the code becomes so complicated

Can you elaborate on reasons why you wouldn't do that?

> Read repair inserts should not be blocking
> ------------------------------------------
>                 Key: CASSANDRA-10726
>                 URL:
>             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out of date replicas is blocking.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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