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From "Michael Theroux (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4905) Repair should exclude gcable tombstones from merkle-tree computation
Date Thu, 23 May 2013 23:00:21 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13665806#comment-13665806
] 

Michael Theroux commented on CASSANDRA-4905:
--------------------------------------------

To followup on my previous comment, I performed the test I described.  The results were quite
incredible.  I brought up three nodes that represented one token range and its replicas. 
These were brought up from very recent snapshots, so some inconsistency was expected.  I ran
the test twice with and without the patch, and on the same data, and periodically monitored
the number of pending compaction tasks.  Below you see a time that it was monitored, and the
number of pending compactions during that time

Without the Patch:

start: 10:30
11:22 - 196
12:33 - 112
13:19 - 1558
14:03 - 1579
14:48 - 1356
15:25 - 1181
16:49 - 752
17:30 - 657
17:52 - 548
18:56 - 202
19:36 - 29
01:50 - 0

With the patch:

start: 3:47
4:34 - 1
4:40 - 1
4:50 - 32
5:01 - 209
5:54 - 1
6:50 - 3 (all streaming from compaction complete)
6:54 - Repair complete, no compactions

Not only was this a very efficient repair from the point of view of the number of compactions,
it also completed in a little over 3 hours, which is equally as dramatic (validation typically
lasts several hours for us).
                
> Repair should exclude gcable tombstones from merkle-tree computation
> --------------------------------------------------------------------
>
>                 Key: CASSANDRA-4905
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4905
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Christian Spriegel
>            Assignee: Sylvain Lebresne
>             Fix For: 1.2.0 beta 3
>
>         Attachments: 4905.txt
>
>
> Currently gcable tombstones get repaired if some replicas compacted already, but some
are not compacted.
> This could be avoided by ignoring all gcable tombstones during merkle tree calculation.
> This was discussed with Sylvain on the mailing list:
> http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/repair-compaction-and-tombstone-rows-td7583481.html

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