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https://issues.apache.org/jira/browse/PIG-580?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Pradeep Kamath updated PIG-580:
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Attachment: PIG-580-v2.patch
Attaching a new version (PIG-580-v2.patch) - the only difference from the
earlier one is that I have removed a debug statement out of
test/org/apache/pig/test/Util.java.
> 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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