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https://issues.apache.org/jira/browse/PIG-171?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Daniel Dai updated PIG-171:
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Attachment: limit2.patch
Attached patch for both "first k sample" and "limited sort". I am still working
on an optimizer to push "POLimit" upward, merge "POLimit" and "POSort" into a
"limited sort".
I also add a syntax "A = ORDER B BY $0 LIMIT 100", so we can test "limited
sort" without the optimizer.
> Top K
> -----
>
> Key: PIG-171
> URL: https://issues.apache.org/jira/browse/PIG-171
> Project: Pig
> Issue Type: New Feature
> Reporter: Amir Youssefi
> Attachments: limit1.patch, limit2.patch
>
>
> Frequently, users are interested on Top results (especially Top K rows) .
> This can be implemented efficiently in Pig /Map Reduce settings to deliver
> rapid results and low Network Bandwidth/Memory usage.
>
> Key point is to prune all data on the map side and keep only small set of
> rows with Top criteria . We can do it in Algebraic function (combiner) with
> multiple value output. Only a small data-set gets out of mapper node.
> The same idea is applicable to solve variants of this problem:
> - An Algebraic Function for 'Top K Rows'
> - An Algebraic Function for 'Top K' values ('Top Rank K' and 'Top Dense
> Rank K')
> - TOP K ORDER BY.
> Another words implementation is similar to combiners for aggregate functions
> but instead of one value we get multiple ones.
> I will add a sample implementation for Top K Rows and possibly TOP K ORDER BY
> to clarify details.
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