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From "Daniel Dai (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-1038) Optimize nested distinct/sort to use secondary key
Date Mon, 02 Nov 2009 17:22:59 GMT

    [ https://issues.apache.org/jira/browse/PIG-1038?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12772562#action_12772562
] 

Daniel Dai commented on PIG-1038:
---------------------------------

Hi, Ashutosh,
I will look into POForeach and find the first nested sort or distinct, and use this sort/distinct
key as the secondary sort key for this map-reduce job. So that I can take away/simplify the
nested sort/distinct.

Yes, we definitely need a framework for the map-reduce layer also. We will work on that, and
welcome any suggestions and comments.

> Optimize nested distinct/sort to use secondary key
> --------------------------------------------------
>
>                 Key: PIG-1038
>                 URL: https://issues.apache.org/jira/browse/PIG-1038
>             Project: Pig
>          Issue Type: Improvement
>          Components: impl
>    Affects Versions: 0.4.0
>            Reporter: Olga Natkovich
>            Assignee: Daniel Dai
>             Fix For: 0.6.0
>
>
> If nested foreach plan contains sort/distinct, it is possible to use hadoop secondary
sort instead of SortedDataBag and DistinctDataBag to optimize the query. 
> Eg1:
> A = load 'mydata';
> B = group A by $0;
> C = foreach B {
>     D = order A by $1;
>     generate group, D;
> }
> store C into 'myresult';
> We can specify a secondary sort on A.$1, and drop "order A by $1".
> Eg2:
> A = load 'mydata';
> B = group A by $0;
> C = foreach B {
>     D = A.$1;
>     E = distinct D;
>     generate group, E;
> }
> store C into 'myresult';
> We can specify a secondary sort key on A.$1, and simplify "D=A.$1; E=distinct D" to a
special version of distinct, which does not do the sorting.

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