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From "Gregory Chanan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3855) Performance degradation of memstore because reseek is linear
Date Tue, 03 Jul 2012 00:32:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13405472#comment-13405472
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Gregory Chanan commented on HBASE-3855:
---------------------------------------

Addendum: I closed because I thought it was confusing to have an issue be open when it was
committed in 0.90.4 and never backed out [and no one is talking about backing it out].  Perhaps
we should create a new bug that tracks backporting HBASE-4195 to 0.90 and, as Andrew suggests,
put [0.90 branch] there?
                
> 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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