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From "Xuefu Zhang (JIRA)" <>
Subject [jira] [Created] (HIVE-8054) Disable hive.optimize.union.remove when hive.execution.engine=spark [Spark Branch]
Date Thu, 11 Sep 2014 18:23:33 GMT
Xuefu Zhang created HIVE-8054:

             Summary: Disable hive.optimize.union.remove when hive.execution.engine=spark
[Spark Branch]
                 Key: HIVE-8054
             Project: Hive
          Issue Type: Improvement
          Components: Spark
            Reporter: Xuefu Zhang

Option hive.optimize.union.remove introduced in HIVE-3276 removes union operators from the
operator graph in certain cases as an optimization reduce the number of MR jobs. While making
sense in MR, this optimization is actually harmful to an execution engine such as Spark, which
natives supports union without requiring additional jobs. This is because removing union operator
creates disjointed operator graphs, each graph generating a job, and thus this optimization
requires more jobs to run the query. Not to mention the additional complexity handling linked
FS descriptors.

I propose that we disable such optimization when the execution engine is Spark.

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