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Posted to dev@pig.apache.org by "Nandor Kollar (JIRA)" <ji...@apache.org> on 2016/12/16 12:35:58 UTC
[jira] [Commented] (PIG-4930) Skewed Join Breaks On Empty Sampled
Input When Key is From Map
[ https://issues.apache.org/jira/browse/PIG-4930?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15754306#comment-15754306 ]
Nandor Kollar commented on PIG-4930:
------------------------------------
[~daijy] would you mind if I would work on this item?
> Skewed Join Breaks On Empty Sampled Input When Key is From Map
> --------------------------------------------------------------
>
> Key: PIG-4930
> URL: https://issues.apache.org/jira/browse/PIG-4930
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.9.2, 0.16.0
> Reporter: William Butler
> Assignee: Daniel Dai
> Fix For: 0.17.0
>
> Attachments: empty_skew.diff
>
>
> When using a skewed join, if the left relation gets its key from a map and said relation is empty, then the skewed join fails during the sampling phase with:
> org.apache.pig.backend.executionengine.ExecException: ERROR 0: Exception while executing (Name: Local Rearrange[tuple]{tuple}(false) - scope-27 Operator Key: scope-27): org.apache.pig.backend.executionengine.ExecException: ERROR 0: Exception while executing [POMapLookUp (Name: POMapLookUp[bytearray] - scope-14 Operator Key: scope-14) children: null at [null[3,17]]]: java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Map
> at org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.processInput(PhysicalOperator.java:314)
> at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POLocalRearrange.getNextTuple(POLocalRearrange.java:287)
> at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.runPipeline(PigGenericMapBase.java:280)
> at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:275)
> at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:65)
> at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
> at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
> at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
> at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:415)
> at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
> at org.apache.hadoop.mapred.Child.main(Child.java:249)
> I think the problem is more fundamental to Pig's skewed join implementation than maps, but it is easily demonstrable with them. I have written an additional test in TestSkewedJoin that demonstrates the problem. The join works correctly if we remove "using 'skewed'"
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