[jira] [Created] (HIVE-9007) Hive may generate wrong plan for map join queries due to IdentityProjectRemover [Spark Branch]

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

Chao created HIVE-9007:
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             Summary: Hive may generate wrong plan for map join queries due to IdentityProjectRemover [Spark Branch]
                 Key: HIVE-9007
                 URL: https://issues.apache.org/jira/browse/HIVE-9007
             Project: Hive
          Issue Type: Sub-task
          Components: Spark
    Affects Versions: spark-branch
            Reporter: Chao


HIVE-8435 introduces a new logical optimizer called IdentityProjectRemover, which may cause map join in spark branch to generate wrong plan.

Currently, the map join conversion in spark branch first goes through a method {{convertJoinMapJoin}}, which replaces a join op with a mapjoin op, removes RS associated with big table, and keep RSs for all small tables. Afterwards, in {{SparkReduceSinkMapJoinProc}} it replaces all parent RSs of the mapjoin op with HTS (note it doesn't check whether the RS belongs to small table or big table.)

The issue arises, when IdentityProjectRemover comes into play, which may result into a situation that a operator tree has two consecutive RSs. Imaging the following example:

{noformat}
          Join               MapJoin
          / \                /   \
        RS   RS   --->     RS     RS
       /      \           /         \
      TS       RS       TS          TS (big table)
                \      (small table)
                 TS
{noformat}

In this case, all parents of the mapjoin op will be RS, even the branch for big table! In {{SparkReduceSinkMapJoinProc}}, they will be replaced with HTS, which is obviously incorrect.




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