[jira] [Commented] (CASSANDRA-2506) Push read repair setting down to the DC-level

["Sylvain Lebresne (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-2506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13147694#comment-13147694 ] 

Sylvain Lebresne commented on CASSANDRA-2506:
---------------------------------------------

On one side, I do like the simplicity of Jonathan proposition (from the point of view of explaining it).
On another side, one thing it doesn't allow is to have some kind of lower chance to pick a node for RR cross-DC versus intra-DC, which is a concept that makes sense (I'm less convinced by the actual usefulness of being able to assign a different RR chance to each DC, but if you have example where it's useful, feel free to share).

But the truth is, the question I want to ask is: is this useful at all in the first place?
Don't get me wrong, in a pre-1.0 world, it would definitively be useful. But in 1.0 we now have reliable hinted-handoffs. RR is still activated but with a low chance and that's only cautionary in case we had bumps on the road with the new HH code. But if HH does work as intended, RR becomes a costly and pretty much useless operation. In that context, do we really want to add more complication to it?
                
> Push read repair setting down to the DC-level
> ---------------------------------------------
>
>                 Key: CASSANDRA-2506
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2506
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>    Affects Versions: 1.0.1
>            Reporter: Brandon Williams
>            Assignee: Vijay
>            Priority: Minor
>             Fix For: 1.0.3
>
>         Attachments: 0001-dc-localized-read-repair-v2.patch, 0001-dc-localized-read-repair.patch, 0002-thrift-and-avro-v2.patch, 0002-thrift-and-avro.patch, 0003-documentation-for-read_repair_options-v2.patch, 0003-documentation-for-read_repair_options.patch
>
>
> Currently, read repair is a global setting.  However, when you have two DCs and use one for analytics, it would be nice to turn it off only for that DC so the live DC serving the application can still benefit from it.

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