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From "Jakub Janecek (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-10740) Incorrect condition causes cleanup of SSTables which might not need it
Date Wed, 25 Nov 2015 10:21:10 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10740?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15026562#comment-15026562
] 

Jakub Janecek commented on CASSANDRA-10740:
-------------------------------------------

[~krummas] I have added a patch with the test. The last test case shows that the change actually
has some effect. The old implementation would return that the SSTable needs a cleanup but
my implementation correctly returns false.

> Incorrect condition causes cleanup of SSTables which might not need it
> ----------------------------------------------------------------------
>
>                 Key: CASSANDRA-10740
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10740
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Jakub Janecek
>             Fix For: 2.1.x
>
>         Attachments: trunk-10740.txt, trunk-test-10740.txt
>
>
> We needed to perform cleanup of SSTables in our production cluster but found out that
it would take several months. Together with my colleague [~JiriHorky] we have pinpointed the
issue to method CompactionManager.needsCleanup which incorrectly marks almost all SSTables
as the ones needing the cleanup even though that might not be true. I am attaching a patch
which should be applicable from version 2.x forward (this is the version we would need it
in).
> To explain the problem, the last condition in the cycle that checks whether the next
key in the SSTable after the current checked range is NOT contained in the next range falsely
marks SSTable as necessary to have cleanup even though it might be contained in some other
range. The correct condition (which is actully described in the comment) is to check whether
the next key in the SSTable after the current range is less than or equal to the "left" key
of the next range (assuming that the left key is exclusive which is described in another comment
of the same method).
> Is our patch and reasoning correct?



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