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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HBASE-16501) seekToPrevoiusRow() can be optimized
Date Thu, 01 Sep 2016 09:33:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15454893#comment-15454893
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ramkrishna.s.vasudevan edited comment on HBASE-16501 at 9/1/16 9:33 AM:
------------------------------------------------------------------------

bq.When the SegmentScanner is created the currentCell is initialized. So in this case, it
will go throw all the cells and see all are above readPnt.

Yes that will be done by the other JIRA HBASE-15871. When we know the read point is already
lesser than the flushed pt then there is no point in adding the memstore scanner itself.


was (Author: ram_krish):
bq.When the SegmentScanner is created the currentCell is initialized. So in this case, it
will go throw all the cells and see all are above readPnt.

Yes that will be done by the other JIRA HBASE-15871. When we know the thread point is already
than the flushed pt then there is no point in adding the memstore scanner itself.

> seekToPrevoiusRow() can be optimized
> ------------------------------------
>
>                 Key: HBASE-16501
>                 URL: https://issues.apache.org/jira/browse/HBASE-16501
>             Project: HBase
>          Issue Type: Improvement
>          Components: Performance, Scanners
>    Affects Versions: 2.0.0
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>             Fix For: 2.0.0
>
>         Attachments: HBASE-16501.patch, HBASE-16501_1.patch, HBASE-16501_sysocount.patch
>
>
> Need to check the details and see how to implement it. But the problem is this
> In seekToPReviousRow impl in case of a reverse scan, say we have rows row10000 to row20000.
We are doing a reverse scan.
> The scan starts from row20000 and we read all columns. Assume this row was skipped due
to mvcc we move to the previous row 'row19999'. Now we read this row19999 and even if this
does not match in mvcc we skip and again read row20000 and do the same. 
> Like this we keep doing til we come to row10000 and this time we read til row20000 just
to k now we have to skip it. The same problem happens in Storefilescanner also and there we
do lot of seek and next(). Better to solve this case. 
> [~zjushch] - FYI.



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