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From "Jonathan Hsieh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3855) Performance degradation of memstore because reseek is linear
Date Sat, 07 Jul 2012 14:58:35 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13408687#comment-13408687
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Jonathan Hsieh commented on HBASE-3855:
---------------------------------------

Ouch! 

Yes, I think we'd like to get HBASE-4195 in o 0.90.7 as well -- not for performance but for
correctness reasons.  
                
> 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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