[jira] [Commented] (CASSANDRA-6440) Repair should allow repairing particular endpoints to reduce WAN usage.

["sankalp kohli (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-6440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13897318#comment-13897318 ] 

sankalp kohli commented on CASSANDRA-6440:
------------------------------------------

[~lyubent]  Looks good. 

> Repair should allow repairing particular endpoints to reduce WAN usage. 
> ------------------------------------------------------------------------
>
>                 Key: CASSANDRA-6440
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6440
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: sankalp kohli
>            Assignee: sankalp kohli
>            Priority: Minor
>         Attachments: 6440_repair.log, JIRA-6440-v2.diff, JIRA-6440-v3.diff, JIRA-6440.diff
>
>
> The way we send out data that does not match over WAN can be improved. 
> Example: Say there are four nodes(A,B,C,D) which are replica of a range we are repairing. A, B is in DC1 and C,D is in DC2. If A does not have the data which other replicas have, then we will have following streams
> 1) A to B and back
> 2) A to C and back(Goes over WAN)
> 3) A to D and back(Goes over WAN)
> One of the ways of doing it to reduce WAN traffic is this.
> 1) Repair A and B only with each other and C and D with each other starting at same time t. 
> 2) Once these repairs have finished, A,B and C,D are in sync with respect to time t. 
> 3) Now run a repair between A and C, the streams which are exchanged as a result of the diff will also be streamed to B and D via A and C(C and D behaves like a proxy to the streams).
> For a replication of DC1:2,DC2:2, the WAN traffic will get reduced by 50% and even more for higher replication factors.
> Another easy way to do this is to have repair command take nodes with which you want to repair with. Then we can do something like this.
> 1) Run repair between (A and B) and (C and D)
> 2) Run repair between (A and C)
> 3) Run repair between (A and B) and (C and D)
> But this will increase the traffic inside the DC as we wont be doing proxy.



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