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https://issues.apache.org/jira/browse/PIG-97?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12567829#action_12567829
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Antonio Magnaghi commented on PIG-97:
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The patch looks good for the POVisitor pattern. I just have comment/question:
it looks like the POPrinter is currently not overriding some of the visitX
methods in the super class (POVisitor), such as visitCogroup, visitSplit,
visitUnion. If the local physical query plan contains such operators no info
would be printed out for those operators
> Jobs produce wrong results when a cogroup is in the script and the compiler
> chooses to use the combiner feature of hadoop.
> --------------------------------------------------------------------------------------------------------------------------
>
> Key: PIG-97
> URL: https://issues.apache.org/jira/browse/PIG-97
> Project: Pig
> Issue Type: Bug
> Components: impl
> Affects Versions: 0.0.0
> Reporter: Alan Gates
> Assignee: Alan Gates
> Attachments: cogroupcombiner.patch
>
>
> The following script will produce 0 output records, even when it should
> produce records:
> a = load 'file1';
> b = load 'file2';
> c = cogroup a by $0, b by $0;
> d = foreach c generate $0, COUNT($1), COUNT($2);
> dump d;
> In this case pig chooses to use the combiner in order to be more efficient.
> However, the following code in PigCombiner.java causes a problem:
> for (int i = 0; i < inputCount; i++) { // XXX: shouldn't we only do this if
> INNER flag is set?
> if (t.getBagField(1 + i).size() == 0) return;
> }
> In this case a map is often running on a machine where it has access to only
> one of the two files and thus there is nothing in one of the bags, so the
> above lines of code cause the combiner to bailout without pushing any tuples
> to the OutputCollector.
> The proposed solution for the short term is to disable use of the combiner in
> cases where more than one file are grouped together.
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