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Date: Tue, 3 Jul 2012 00:12:58 +0000 (UTC)
From: "Gregory Chanan (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Resolved] (HBASE-3855) Performance degradation of memstore
 because reseek is linear
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     [ https://issues.apache.org/jira/browse/HBASE-3855?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Gregory Chanan resolved HBASE-3855.
-----------------------------------

       Resolution: Fixed
    Fix Version/s:     (was: 0.90.7)
                   0.90.4

It looks like this was committed way back in 0.90.4.  Closing.

commit 4f4edbaa043952715d4eb9a40605154c6e41d179
Author: Michael Stack <stack@apache.org>
Date:   Fri Jun 10 19:21:41 2011 +0000

    HBASE-3855 Performance degradation of memstore because reseek is linear
    
    git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.90@1134419 13f79535-47bb-0310-9956-ffa450edef68

Perhaps this was left open for HBASE-4195 (which never made it into 0.90).
                
> Performance degradation of memstore because reseek is linear
> ------------------------------------------------------------
>
>                 Key: HBASE-3855
>                 URL: https://issues.apache.org/jira/browse/HBASE-3855
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: dhruba borthakur
>            Priority: Critical
>             Fix For: 0.90.4
>
>         Attachments: memstoreReseek.txt, memstoreReseek2.txt
>
>
> The scanner use reseek to find the next row (or next column) as part of a scan. The reseek code iterates over a Set to position itself at the right place. If there are many thousands of kvs that need to be skipped over, then the time-cost is very high. In this case, a seek would be far lesser in cost than a reseek.

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