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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-3784) de-emphasize mapjoin hint
Date Mon, 10 Dec 2012 06:21:21 GMT
Namit Jain created HIVE-3784:
--------------------------------

             Summary: de-emphasize mapjoin hint
                 Key: HIVE-3784
                 URL: https://issues.apache.org/jira/browse/HIVE-3784
             Project: Hive
          Issue Type: Improvement
          Components: Query Processor
            Reporter: Namit Jain
            Assignee: Namit Jain


hive.auto.convert.join has been around for a long time, and is pretty stable.
When mapjoin hint was created, the above parameter did not exist.

The only reason for the user to specify a mapjoin currently is if they want
it to be converted to a bucketed-mapjoin or a sort-merge bucketed mapjoin.
Eventually, that should also go away, but that may take some time to stabilize.

There are many rules in SemanticAnalyzer to handle the following trees:

ReduceSink -> MapJoin
Union      -> MapJoin
MapJoin    -> MapJoin

This should not be supported anymore. In any of the above scenarios, the
user can get the mapjoin behavior by setting hive.auto.convert.join to true
and not specifying the hint. This will simplify the code a lot.

What does everyone think ?

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