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From "Raymond Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8012) Reseek should position to the beginning of file for the first time it is invoked with a KV smaller than the first KV in file
Date Fri, 08 Mar 2013 07:18:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8012?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13596913#comment-13596913

Raymond Liu commented on HBASE-8012:

[~stack] : I think this patch won't do any performance benefit at present. It just make reseekto
's behavior more correct and simulate the behavior of seekto. it doesn't need to have extra
place to keep tracking whether can we do reseek or not. reseek it self should always working
correctly. ( since seek can why reseek should not).  And I don't see downsides possibility,
since the check need to be done anyway, if not inside reseek than before call reseek.

While, as I mentioned before, If we are allowed to change the seekto and reseekto 's behavior,
we can push this check into even lower level. at that case, could have micro level performance
benefit. Since in some code branch, it won't need to be checked at all.
> Reseek should position to the beginning of file for the first time it is invoked with
a KV smaller than the first KV in file
> ----------------------------------------------------------------------------------------------------------------------------
>                 Key: HBASE-8012
>                 URL: https://issues.apache.org/jira/browse/HBASE-8012
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.94.5
>            Reporter: Raymond Liu
>            Assignee: Raymond Liu
>            Priority: Minor
>             Fix For: 0.98.0
>         Attachments: HBASE-8012.patch, HBASE-8012.patch, HBASE-8012_v2.patch
> The storeFileScanner's seekAtOrAfter method will position at the beginning of the file
when the passed KV is smaller than first KV in file. While for reseekAtOrAfter, I think it
should also do the same thing when it is the first time it been seeked. originally, this is
workaround by adding a isReseekable property in StoreFileScanner, and is checked upon each
enforceSeek(), if it is not seeked before, it will go with seek approaching instead of reseek
approaching. While why not make reseekAtOrAfter working correctly for the first time it been
reseek (also never been seek before), since the file is never seeked before, so position it
at the beginning of the file don't break the idea of "reseek", say never rewind.
> It will save the effort for HBASE-8001, with this fixed, it won't need to check isReseekable
any more.

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