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From "Tyler Hobbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8993) EffectiveIndexInterval calculation is incorrect
Date Wed, 25 Mar 2015 19:10:53 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14380553#comment-14380553
] 

Tyler Hobbs commented on CASSANDRA-8993:
----------------------------------------

bq. Might it be easier to filter the list of readers earlier

Sure, there's no good reason not to do this earlier, so I've moved it to the suggested location.

bq. Could you clarify SSTableReader Line 875: why do we check BASE_SAMPLING_LEVEL entries?

I meant to explain this a little better, thanks for catching that.  I've improved the comment
enough that it should hopefully clarify the reason.

My [branch|https://github.com/thobbs/cassandra/tree/CASSANDRA-8993] has been updated in addition
to the v2 patch.

> EffectiveIndexInterval calculation is incorrect
> -----------------------------------------------
>
>                 Key: CASSANDRA-8993
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8993
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>            Priority: Blocker
>             Fix For: 2.1.4
>
>         Attachments: 8993-2.1-v2.txt, 8993-2.1.txt, 8993.txt
>
>
> I'm not familiar enough with the calculation itself to understand why this is happening,
but see discussion on CASSANDRA-8851 for the background. I've introduced a test case to look
for this during downsampling, but it seems to pass just fine, so it may be an artefact of
upgrading.
> The problem was, unfortunately, not manifesting directly because it would simply result
in a failed lookup. This was only exposed when early opening used firstKeyBeyond, which does
not use the effective interval, and provided the result to getPosition().
> I propose a simple fix that ensures a bug here cannot break correctness. Perhaps [~thobbs]
can follow up with an investigation as to how it actually went wrong?



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