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https://issues.apache.org/jira/browse/PIG-3557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13871484#comment-13871484
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Daniel Dai commented on PIG-3557:
---------------------------------
Yes, in case of the root vertex (vertex contains load), the parallelism is
determined by InputFormat not requestedParallelism, and it cannot be determined
in compile time. We will need to do a second limit only vertex in this case.
For non-root vertex however, we can use requestedParallelism as a criteria to
determine whether or not we need a follow up vertex for limit.
> Implement optimizations for LIMIT
> ---------------------------------
>
> Key: PIG-3557
> URL: https://issues.apache.org/jira/browse/PIG-3557
> Project: Pig
> Issue Type: Sub-task
> Components: tez
> Affects Versions: tez-branch
> Reporter: Alex Bain
> Assignee: Alex Bain
>
> Implement optimizations for LIMIT when other parts of Pig-on-Tez are more
> mature. Some of the optimizations mentioned by Daniel include:
> 1. If the previous stage using 1 reduce, no need to add one more vertex
> 2. If the limitplan is null (ie, not the "limited order by" case), we might
> not need a shuffle edge, a pass through edge should be enough if possible
> 3. Similar to PIG-1270, we can push limit to InputHandler
> 4. We also need to think through the "limited order by" case once "order by"
> is implemented
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