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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13109) Make better SEEK vs SKIP decisions during scanning
Date Tue, 03 Mar 2015 04:55:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14344510#comment-14344510
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Lars Hofhansl commented on HBASE-13109:
---------------------------------------

Some more test with many HFiles (4m rows, 5 cols, 1 version - as above). No compactions at
all -> 25 HFiles of 10mb each.

Without patch:
||Wildcard||Col 2+4||
|4.59|13.5|

With patch:
||Wildcard||Col 2+4||
|4.38|4.89|

Almost a 3x improvement. I have convinced myself that this is good.

Somebody up for independent tests? I have a 0.98 patch as well (in fact that's the one I have
used for testing)?


> Make better SEEK vs SKIP decisions during scanning
> --------------------------------------------------
>
>                 Key: HBASE-13109
>                 URL: https://issues.apache.org/jira/browse/HBASE-13109
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Priority: Minor
>         Attachments: 13109-trunk-v2.txt, 13109-trunk-v3.txt, 13109-trunk-v4.txt, 13109-trunk.txt
>
>
> I'm re-purposing this issue to add a heuristic as to when to SEEK and when to SKIP Cells.
This has come up in various issues, and I think I have a way to finally fix this now. HBASE-9778,
HBASE-12311, and friends are related.
> --- Old description ---
> This is a continuation of HBASE-9778.
> We've seen a scenario of a very slow scan over a region using a timerange that happens
to fall after the ts of any Cell in the region.
> Turns out we spend a lot of time seeking.
> Tested with a 5 column table, and the scan is 5x faster when the timerange falls before
all Cells' ts.
> We can use the lookahead hint introduced in HBASE-9778 to do opportunistic SKIPing before
we actually seek.



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