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From "Daniel Dai (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-171) Top K
Date Tue, 01 Jul 2008 17:36:44 GMT

     [ https://issues.apache.org/jira/browse/PIG-171?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Daniel Dai updated PIG-171:
---------------------------

    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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