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https://issues.apache.org/jira/browse/PIG-2779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13424224#comment-13424224
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Jie Li commented on PIG-2779:
-----------------------------
Agreed with #1.
Re #2, according to http://pig.apache.org/docs/r0.10.0/perf.html#parallel,
these operators support PARALLEL:
COGROUP, CROSS, DISTINCT, GROUP, JOIN (inner), JOIN (outer), and ORDER BY.
We need to make sure the PARALLEL associate with these operators remains same
across logic/phycical/mr phases. Seems it suffers from the same complexity
faced by requestedParallel, such as query transformation, multi-query
optimization, etc. Seems it's not trivial?
> 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, 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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