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From "Vinod Kumar Vavilapalli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3784) de-emphasize mapjoin hint
Date Thu, 13 Dec 2012 20:40:12 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531451#comment-13531451
] 

Vinod Kumar Vavilapalli commented on HIVE-3784:
-----------------------------------------------

Hi, couple of questsions:
 - Does this rule out bucketed map-join or hive.optimize.bucketmapjoin will continue to work?
If it is the earlier, shouldn't fixing that be a blocker of this?
 - Also, does this rule out map join of multiple small tables in a single map-only job? As
discussed on HIVE-3652, giving map-join hints to a nested join automatically converts it into
a single map-join map.

bq. also optimizes a lot of queries - mapjoin followed by groupby.
This is great!
                
> 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
>         Attachments: hive.3784.1.patch, hive.3784.2.patch, hive.3784.3.patch, hive.3784.4.patch
>
>
> 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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