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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9778) Avoid seeking to next column in ExplicitColumnTracker when possible
Date Wed, 16 Oct 2013 14:35:47 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13796834#comment-13796834
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Lars Hofhansl commented on HBASE-9778:
--------------------------------------

[~stack], skip means that it'll skip this particular KV (i.e. this version of a column).
[~jmspaggi], yeah, the test failure is probably related :)  Will take a look today.

I also realized yesterday that the patch is not quite correct anyway. What the tracker needs
to know is maxVersions of the ColumnFamily not maxVersions of this particular scan (which
is min of the scan' and CF's setting).


> Avoid seeking to next column in ExplicitColumnTracker when possible
> -------------------------------------------------------------------
>
>                 Key: HBASE-9778
>                 URL: https://issues.apache.org/jira/browse/HBASE-9778
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.98.0, 0.94.13, 0.96.1
>
>         Attachments: 9778-0.94.txt, 9778-trunk.txt
>
>
> The issue of slow seeking in ExplicitColumnTracker was brought up by [~vrodionov] on
the dev list.
> My idea here is to avoid the seeking if we know that there aren't many versions to skip.
> How do we know? We'll use the column family's VERSIONS setting as a hint. If VERSIONS
is set to 1 (or maybe some value < 10) we'll avoid the seek and call SKIP repeatedly.
> HBASE-9769 has some initial number for this approach:
> Interestingly it depends on which column(s) is (are) selected.
> Some numbers: 4m rows, 5 cols each, 1 cf, 10 bytes values, VERSIONS=1, everything filtered
at the server with a ValueFilter. Everything measured in seconds.
> Without patch:
> ||Wildcard||Col 1||Col 2||Col 4||Col 5||Col 2+4||
> |6.4|8.5|14.3|14.6|11.1|20.3|
> With patch:
> ||Wildcard||Col 1||Col 2||Col 4||Col 5||Col 2+4||
> |6.4|8.4|8.9|9.9|6.4|10.0|
> Variation here was +- 0.2s.
> So with this patch scanning is 2x faster than without in some cases, and never slower.
No special hint needed, beyond declaring VERSIONS correctly.



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