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https://issues.apache.org/jira/browse/CASSANDRA-6440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13866693#comment-13866693
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Jonathan Ellis commented on CASSANDRA-6440:
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I'd rather fail the operation if they give an invalid configuration rather than
try to guess what they "really" meant.
> 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.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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