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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9915) Severe performance bug: isSeeked() in EncodedScannerV2 is always false
Date Thu, 07 Nov 2013 21:47:18 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13816463#comment-13816463
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Lars Hofhansl commented on HBASE-9915:
--------------------------------------

Checked again. My first patch should be safer. block == null should be equivalent to seeker
== null, but at other places we change block != null, so it's better to do this here as well.

> Severe performance bug: isSeeked() in EncodedScannerV2 is always false
> ----------------------------------------------------------------------
>
>                 Key: HBASE-9915
>                 URL: https://issues.apache.org/jira/browse/HBASE-9915
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.98.0, 0.96.1, 0.94.14
>
>         Attachments: 9915-0.94.txt, 9915-trunk.txt, profile.png
>
>
> While debugging why reseek is so slow I found that it is quite broken for encoded scanners.
> The problem is this:
> AbstractScannerV2.reseekTo(...) calls isSeeked() to check whether scanner was seeked
or not. If it was it checks whether the KV we want to seek to is in the current block, if
not it always consults the index blocks again.
> isSeeked checks the blockBuffer member, which is not used by EncodedScannerV2 and thus
always returns false, which in turns causes an index lookup for each reseek.



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