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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3598) physical optimizer changes for auto sort-merge join
Date Thu, 18 Oct 2012 20:06:02 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3598?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13479310#comment-13479310
] 

Namit Jain commented on HIVE-3598:
----------------------------------

After HIVE-3403, an auto sortmerge join can be performed.
However, consider the following scenario:

T1 - big table: 3 partitions : big partitions
T2 - small table: 1 partition

both T1 and T2 are sorted/bucketed on the same key.

If a join is being performed between T1 and T2, with HIVE-3403, T2 would be picked up as the
table on which the mapper would run.
Ideally, if T2 is so small that it can fit in memory, a better approach would be map-join.

The physical optimizer should change the sort-merge join task into a backup task, with all
tables being candidates for map-join
(similar to auto convert mapjoin).

                
> physical optimizer changes for auto sort-merge join
> ---------------------------------------------------
>
>                 Key: HIVE-3598
>                 URL: https://issues.apache.org/jira/browse/HIVE-3598
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Namit Jain
>


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