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https://issues.apache.org/jira/browse/CASSANDRA-3200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13104324#comment-13104324
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Peter Schuller commented on CASSANDRA-3200:
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This is definitely an interesting idea. But FWIW, I think it is more important
to make repair be more incremental/less bulky/more continuous than it is to be
efficient in terms of absolute amount of data transfered. I wonder to what
extent an implementation of this ticket might be obsoleted by a solution to
CASSANDRA-2699 (not that the desire to not transfer things unnecessarily goes
away, but in terms of the implementation details).
> Repair: compare all trees together (for a given range/cf) instead of by pair
> in isolation
> -----------------------------------------------------------------------------------------
>
> Key: CASSANDRA-3200
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3200
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Sylvain Lebresne
> Assignee: Sylvain Lebresne
> Priority: Minor
> Labels: repair
> Fix For: 1.0.1
>
>
> Currently, repair compare merkle trees by pair, in isolation of any other
> tree. What that means concretely is that if I have three node A, B and C
> (RF=3) with A and B in sync, but C having some range r inconsitent with both
> A and B (since those are consistent), we will do the following transfer of r:
> A -> C, C -> A, B -> C, C -> B.
> The fact that we do both A -> C and C -> A is fine, because we cannot know
> which one is more to date from A or C. However, the transfer B -> C is
> useless provided we do A -> C if A and B are in sync. Not doing that transfer
> will be a 25% improvement in that case. With RF=5 and only one node
> inconsistent with all the others, that almost a 40% improvement, etc...
> Given that this situation of one node not in sync while the others are is
> probably fairly common (one node died so it is behind), this could be a fair
> improvement over what is transferred. In the case where we use repair to
> rebuild completely a node, this will be a dramatic improvement, because it
> will avoid the rebuilded node to get RF times the data it should get.
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