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https://issues.apache.org/jira/browse/PIG-1038?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12777589#action_12777589
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Daniel Dai commented on PIG-1038:
---------------------------------

Continue with the last comment.

4. Strip secondary keys from the value

5. Write a byte version of OutputKeyComparator

> 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
>
>         Attachments: PIG-1038-1.patch, PIG-1038-2.patch, PIG-1038-3.patch, 
> PIG-1038-4.patch, PIG-1038-5.patch
>
>
> 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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