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https://issues.apache.org/jira/browse/PIG-2779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13424625#comment-13424625
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Bill Graham commented on PIG-2779:
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I'm going to take a look to see what it would take to implement
{{pig.info.reducers.keyword.parallel}} without refactoring
{{requestedParallel}}, since I'm not sure we want to take that on.
> Refactoring the code for setting number of reducers
> ---------------------------------------------------
>
> Key: PIG-2779
> URL: https://issues.apache.org/jira/browse/PIG-2779
> Project: Pig
> Issue Type: Bug
> Reporter: Jie Li
> Assignee: Jie Li
> Fix For: 0.11
>
> Attachments: PIG-2779.0.patch, PIG-2779.1.patch, PIG-2779.2.patch,
> PIG-2779.3.patch, PIG-2779.4.patch, TestNumberOfReducers.java,
> TestNumberOfReducers.java
>
>
> As PIG-2652 observed, currently the code for setting number of reducers is a
> little messy. MapReduceOper.requestedParallelism seems being misused in some
> plases, and now we support runtime estimation of #reducer which further
> complicates the problem.
> For example, if we specify parallel 1 for the order-by, the estimated
> #reducer will be used. If we specify parallel 2 while it estimates 4,
> order-by will fail due to "Illegal partition for Null". If we specify
> parallel 4 while it estimates 2, then some reducers will have nothing to do.
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