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From "Jeremiah Jordan (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-10726) Read repair inserts should not be blocking
Date Wed, 01 Nov 2017 13:25:00 GMT


Jeremiah Jordan commented on CASSANDRA-10726:

{quote}And I'm leaning towards these three settings:
1. Perform blocking RR (current default, left default)
2. Write hints instead of sending RR mutations, and let hint delivery repair the inconsistency,
in a manner decoupled from the original read request
3. Do nothing, for those who rely on regular repair for one reason or another (thinking TWCS,
DTCS users?){quote}

I think the current default needs to stay the default (I was bitten by the original problem
more than once in the 0.6/0.7 days), but giving advanced users the ability to disable that
seems fine to me.  +1 to those options.

> Read repair inserts should not be blocking
> ------------------------------------------
>                 Key: CASSANDRA-10726
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Coordination
>            Reporter: Richard Low
>            Assignee: Xiaolong Jiang
>            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out of date replicas is blocking.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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