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