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Date: Mon, 5 Jan 2009 15:59:44 -0800 (PST)
From: "Olga Natkovich (JIRA)" <jira@apache.org>
To: pig-dev@hadoop.apache.org
Subject: [jira] Updated: (PIG-580) PERFORMANCE: Combiner should also be used
 when there are distinct aggregates in a foreach following a group provided
 there are no non-algebraics in the foreach
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     [ https://issues.apache.org/jira/browse/PIG-580?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Olga Natkovich updated PIG-580:
-------------------------------

    Resolution: Fixed
        Status: Resolved  (was: Patch Available)

patch committed; thanks, pradeep

> PERFORMANCE: Combiner should also be used when there are distinct aggregates in a foreach following a group provided there are no non-algebraics in the foreach 
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: PIG-580
>                 URL: https://issues.apache.org/jira/browse/PIG-580
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: types_branch
>            Reporter: Pradeep Kamath
>            Assignee: Pradeep Kamath
>             Fix For: types_branch
>
>         Attachments: PIG-580-v2.patch, PIG-580.patch
>
>
> Currently Pig uses the combiner only when there is foreach following a group when the elements in the foreach generate have the following characteristics:
> 1) simple project of the "group" column
> 2) Algebraic UDF
> The above conditions exclude use of the combiner for distinct aggregates - the distinct operation itself is combinable (irrespective of whether it feeds to an algebraic or non algebraic udf). So if the following foreach should also be combinable:
> {code}
> ..
> b = group a by $0;
> c = foreach b generate { x = distinct a; generate group, COUNT(x), SUM(x.$1) }
> {code}
> The combiner optimizer should cause the distinct to be combined and the final combine output should feed the COUNT() and SUM() in the reduce.

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