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Date: Thu, 7 Nov 2013 19:39:17 +0000 (UTC)
From: "Jean-Marc Spaggiari (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12678045.1383852058578.36814.1383853157691@arcas>
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Subject: [jira] [Commented] (HBASE-9915) Severe performance bug: isSeeked()
 in EncodedScannerV2 is always false
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    [ https://issues.apache.org/jira/browse/HBASE-9915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13816329#comment-13816329 ] 

Jean-Marc Spaggiari commented on HBASE-9915:
--------------------------------------------

Have you compared the performances with and without? I have a fresh 0.94 perf test running, I can try to apply this and re-run to see the difference...

> 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, 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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