[jira] [Created] (HIVE-6041) Incorrect task dependency graph for skewed join optimization

["Adrian Popescu (JIRA)" <ji...@apache.org>]

Adrian Popescu created HIVE-6041:
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             Summary: Incorrect task dependency graph for skewed join optimization
                 Key: HIVE-6041
                 URL: https://issues.apache.org/jira/browse/HIVE-6041
             Project: Hive
          Issue Type: Bug
          Components: Query Processor
    Affects Versions: 0.11.0
         Environment: Hadoop 1.0.3
            Reporter: Adrian Popescu
            Priority: Critical


The dependency graph among task stages is incorrect for the skewed join optimized plan. Skewed joins are enabled through "hive.optimize.skewjoin". For the case that skewed keys do not exist, all tasks following the common join are filtered out.

In particular, the conditional task in the optimized plan maintains no dependency with the child tasks of the common join task in the original plan. The conditional task is composed of the map join task which
maintains all these dependencies, but for the case the map join task is filtered out (i.e., no skewed keys exist), all these dependencies are lost. Hence, all the other task stages of the query are skipped.

The bug resides in "ql/optimizer/physical/GenMRSkewJoinProcessor.java", processSkewJoin() function,
immediately after the ConditionalTask is created and its dependencies are set.



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