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')
> 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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