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Date: Fri, 17 Nov 2017 22:42:00 +0000 (UTC)
From: "Blake Eggleston (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12913901.1447799068000.270923.1510958520566@Atlassian.JIRA>
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Subject: [jira] [Commented] (CASSANDRA-10726) Read repair inserts should not
 be blocking
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archived-at: Fri, 17 Nov 2017 22:42:05 -0000


    [ https://issues.apache.org/jira/browse/CASSANDRA-10726?page=3Dcom.atla=
ssian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=
=3D16257697#comment-16257697 ]=20

Blake Eggleston commented on CASSANDRA-10726:
---------------------------------------------

I opened CASSANDRA-14058 for the refactor since that's sort of a separate t=
ask and to keep refactor discussion out of this ticket. There's an initial =
implementation up, take a look and let me know what you think.=20

> Read repair inserts should not be blocking
> ------------------------------------------
>
>                 Key: CASSANDRA-10726
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1072=
6
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Coordination
>            Reporter: Richard Low
>            Assignee: Xiaolong Jiang
>             Fix For: 4.x
>
>
> Today, if there=E2=80=99s a digest mismatch in a foreground read repair, =
the insert to update out of date replicas is blocking. This means, if it fa=
ils, 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), al=
l 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 a=
ny 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 n=
ot be blocking or we should return success for the read even if the write t=
imes out.


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