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From "Nandor Kollar (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (PIG-4930) Skewed Join Breaks On Empty Sampled Input When Key is From Map
Date Sun, 18 Dec 2016 19:27:59 GMT

     [ https://issues.apache.org/jira/browse/PIG-4930?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Nandor Kollar updated PIG-4930:
-------------------------------
    Status: Patch Available  (was: Open)

> 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: 0.16.0, 0.9.2
>            Reporter: William Butler
>            Assignee: Nandor Kollar
>             Fix For: 0.17.0
>
>         Attachments: PIG-4930.patch, 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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