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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13109) Make better SEEK vs SKIP decisions during scanning
Date Mon, 02 Mar 2015 06:43:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14342839#comment-14342839
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stack commented on HBASE-13109:
-------------------------------

Should Scan.LOOK_AHEAD be deprecated/become a noop in case someone using it?

We need to add more compare to KV? There ain't enough going on in there already (smile)?

getNextIndexedKey makes sense but should we be returning byte [] ?  Why not Cell? byte []
presumes a certain format?

getKeyForNextRow is commented out. Remove?

I like the way you add in this optimize method and it works or it doesn't.

When will optimize be optimal?  When will it not add value ( you say selecting 2 and 4 in
above is worse case but generally?) Sorry for dumb questions. I don't know this stuff well.









> 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.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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