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Posted to commits@cassandra.apache.org by "Marcus Eriksson (JIRA)" <ji...@apache.org> on 2017/11/29 12:27:00 UTC
[jira] [Commented] (CASSANDRA-3200) Repair: compare all trees
together (for a given range/cf) instead of by pair in isolation
[ https://issues.apache.org/jira/browse/CASSANDRA-3200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16270669#comment-16270669 ]
Marcus Eriksson commented on CASSANDRA-3200:
--------------------------------------------
pushed another commit with the review fixes here: https://github.com/krummas/cassandra/commits/marcuse/CASSANDRA-3200
tests ran here: https://builds.apache.org/view/A-D/view/Cassandra/job/Cassandra-devbranch-dtest/440/ - looks like one of the new tests failed but it passes locally and it looks like an environment issue. Rerunning [here|https://builds.apache.org/view/A-D/view/Cassandra/job/Cassandra-devbranch-dtest/441/] to make sure
dtest branch is: https://github.com/krummas/cassandra-dtest/commits/marcuse/mt_calcs
> 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
> Reporter: Sylvain Lebresne
> Assignee: Marcus Eriksson
> Priority: Minor
> Labels: repair
> Fix For: 4.x
>
>
> 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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