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From "sankalp kohli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8177) sequential repair is much more expensive than parallel repair
Date Fri, 24 Oct 2014 20:24:36 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8177?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14183413#comment-14183413
] 

sankalp kohli commented on CASSANDRA-8177:
------------------------------------------

One of the things could be somehow snapshots are being deleted which leads to different Merkle
tree. We should log when we generate Merkle tree from snapshot. 
Also we should fail the repair if not all replicas are using the same snapshot. 
[~yukim] Should I create a JIRA to also confirm that all Merkle tree is coming from same snapshot
created for same session id? 

> sequential repair is much more expensive than parallel repair
> -------------------------------------------------------------
>
>                 Key: CASSANDRA-8177
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8177
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Sean Bridges
>            Assignee: Yuki Morishita
>         Attachments: cassc-week.png, iostats.png
>
>
> This is with 2.0.10
> The attached graph shows io read/write throughput (as measured with iostat) when doing
repairs.
> The large hump on the left is a sequential repair of one node.  The two much smaller
peaks on the right are parallel repairs.
> This is a 3 node cluster using vnodes (I know vnodes on small clusters isn't recommended).
 Cassandra reports load of 40 gigs.
> We noticed a similar problem with a larger cluster.



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