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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3784) de-emphasize mapjoin hint
Date Fri, 14 Dec 2012 05:08:13 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13532052#comment-13532052
] 

Namit Jain commented on HIVE-3784:
----------------------------------

>>> 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?

That will continue to work.

>>> 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.

No. If the join key is the same, it will be a single MR job as today.
With different join keys, it needs some work to merge into a single MR anyway - that work
is independent of this change.

As I said before, with this jira, everything that explicitly needs a map-join hint will continue
to work as is.
Whatever is being de-supported did not need a explicit mapjoin hint in the first place.
                
> 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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