William Butler created PIG-4930: ----------------------------------- 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'" -- This message was sent by Atlassian JIRA (v6.3.4#6332)