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https://issues.apache.org/jira/browse/PIG-984?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12764902#action_12764902
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Hadoop QA commented on PIG-984:
-------------------------------

+1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12421908/PIG-984_1.patch
  against trunk revision 824446.

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 3 new or modified tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac 
compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs warnings.

    +1 release audit.  The applied patch does not increase the total number of 
release audit warnings.

    +1 core tests.  The patch passed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: 
http://hudson.zones.apache.org/hudson/job/Pig-Patch-h7.grid.sp2.yahoo.net/73/testReport/
Findbugs warnings: 
http://hudson.zones.apache.org/hudson/job/Pig-Patch-h7.grid.sp2.yahoo.net/73/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: 
http://hudson.zones.apache.org/hudson/job/Pig-Patch-h7.grid.sp2.yahoo.net/73/console

This message is automatically generated.

> PERFORMANCE: Implement a map-side group operator to speed up processing of 
> ordered data 
> ----------------------------------------------------------------------------------------
>
>                 Key: PIG-984
>                 URL: https://issues.apache.org/jira/browse/PIG-984
>             Project: Pig
>          Issue Type: New Feature
>            Reporter: Richard Ding
>            Assignee: Richard Ding
>         Attachments: PIG-984.patch, PIG-984_1.patch
>
>
> The general group by operation in Pig needs both mappers and reducers (the 
> aggregation is done in reducers). This incurs disk writes/reads  between 
> mappers and reducers.
> However, in the cases where the input data has the following properties
>    1. The records with the same key are grouped together (such as the data is 
> sorted by the keys).
>    2. The records with the same key are in the same mapper input.
> the group by operation can be performed in the mappers only and thus remove 
> the overhead of disk writes/reads.
> Alan proposed adding a hint to the group by clause like this one:
> {code}
> A = load 'input' using SomeLoader(...);
> B = group A by $0 using "mapside";
> C = foreach B generate ...
> {code}
> The proposed addition of using "mapside" to group will be a mapside group 
> operator that collects all records for a given key into a buffer. When it 
> sees a key change it will emit the key and bag for records it had buffered. 
> It will assume that all keys for a given record are collected together and 
> thus there is not need to buffer across keys. 
> It is expected that "SomeLoader" will be implemented by data systems such as 
> Zebra to ensure the data emitted by the loader satisfies the above properties 
> (1) and (2).
> It will be the responsibility of the user (or the loader) to guarantee these 
> properties (1) & (2) before invoking the mapside hint for the group by 
> clause. The Pig runtime can't check for the errors in the input data.
> For the group by clauses with mapside hint, Pig Latin will only support group 
> by columns (including *), not group by expressions nor group all. 
>   

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