[jira] Assigned: (PIG-171) Top K

["Alan Gates (JIRA)" <ji...@apache.org>]

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

Alan Gates reassigned PIG-171:
------------------------------

    Assignee: Daniel Dai

> Top K
> -----
>
>                 Key: PIG-171
>                 URL: https://issues.apache.org/jira/browse/PIG-171
>             Project: Pig
>          Issue Type: Sub-task
>    Affects Versions: 0.2.0
>            Reporter: Amir Youssefi
>            Assignee: Daniel Dai
>             Fix For: 0.2.0
>
>         Attachments: limit1.patch, limit2.patch, limit3.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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