[jira] [Created] (PIG-4930) Skewed Join Breaks On Empty Sampled Input When Key is From Map

["William Butler (JIRA)" <ji...@apache.org>]

William Butler created PIG-4930:
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             Summary: 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


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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