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https://issues.apache.org/jira/browse/PIG-1590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12905207#action_12905207
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Ashutosh Chauhan commented on PIG-1590:
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It will entail changes in POMergeJoin and LogToPhyTranslationVisitor.
> Use POMergeJoin for Left Outer Join when join using 'merge'
> -----------------------------------------------------------
>
> Key: PIG-1590
> URL: https://issues.apache.org/jira/browse/PIG-1590
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Affects Versions: 0.8.0
> Reporter: Ashutosh Chauhan
> Priority: Minor
>
> C = join A by $0 left, B by $0 using 'merge';
> will result in map-side sort merge join. Internally, it will translate to use
> POMergeCogroup + ForEachFlatten. POMergeCogroup places quite a few
> restrictions on its loaders (A and B in this case) which is cumbersome.
> Currently, only Zebra is known to satisfy all those requirements. It will be
> better to use POMergeJoin in this case, since it has far fewer requirements
> on its loader. Importantly, it works with PigStorage. Plus, POMergeJoin will
> be faster then POMergeCogroup + FE-Flatten.
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