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From "Billie Rinaldi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2539) SummingCombiner does not adhere to Combiner#COLUMNS_OPTION
Date Tue, 25 Mar 2014 02:59:45 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13946065#comment-13946065
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Billie Rinaldi commented on ACCUMULO-2539:
------------------------------------------

Combiner never combines values across keys with different columns.  It combines values for
keys that differ in timestamp only.  So, if you specify a column family, every qualifier in
that family will be combined individually, they won't be combined together into a single value
for the family.  Same with the all columns option -- it doesn't combine all the columns into
a single value, it's just an easier way to configure the same combiner for each individual
column in the table.  (There are also a couple of unused imports in the patch.)

> SummingCombiner does not adhere to Combiner#COLUMNS_OPTION
> ----------------------------------------------------------
>
>                 Key: ACCUMULO-2539
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2539
>             Project: Accumulo
>          Issue Type: Bug
>          Components: client
>    Affects Versions: 1.4.4, 1.5.1
>            Reporter: Josh Elser
>            Assignee: Josh Elser
>             Fix For: 1.4.5, 1.5.2, 1.6.1
>
>         Attachments: 0001-ACCUMULO-2539-Expand-javadoc-for-Combiner-to-be-more.patch
>
>
> In testing out the SummingCombiner, I set the Combiner#COLUMNS_OPTION which led me to
believe that the SummingCombiner would limit columns to the set that is provided as an option
through the IteratorSetting.
> In practice, this was not the case as Combiner#findTop isn't used, and thus that column
list is not adhered to. I can get the expected functionality out of SummingCombiner by calling
{{ScannerBase#fetchColumn}} or {{ScannerBase#fetchColumnFamily}}.



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