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From "Namit Jain (JIRA)" <>
Subject [jira] Commented: (HIVE-1194) sorted merge join
Date Wed, 03 Mar 2010 19:04:27 GMT


Namit Jain commented on HIVE-1194:

PREHOOK: query: select /*+mapjoin(a,b)*/ * from smb_bucket_1 a right outer join smb_bucket_2
b on a.key \
= b.key join smb_bucket_3 c on b.key=c.key
PREHOOK: Input: default@smb_bucket_2
PREHOOK: Input: default@smb_bucket_3
PREHOOK: Input: default@smb_bucket_1
PREHOOK: Output: file:/Users/heyongqiang/Documents/workspace/Hive-Test/build/ql/scratchdir/hive_2010-03-\
POSTHOOK: query: select /*+mapjoin(a,b)*/ * from smb_bucket_1 a right outer join smb_bucket_2
b on a.key\
 = b.key join smb_bucket_3 c on b.key=c.key
POSTHOOK: Input: default@smb_bucket_2
POSTHOOK: Input: default@smb_bucket_3
POSTHOOK: Input: default@smb_bucket_1
POSTHOOK: Output: file:/Users/heyongqiang/Documents/workspace/Hive-Test/build/ql/scratchdir/hive_2010-03\

Why is this giving a empty result ?

> sorted merge join
> -----------------
>                 Key: HIVE-1194
>                 URL:
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: He Yongqiang
>             Fix For: 0.6.0
>         Attachments: hive-1194-2010-02-28.patch, hive-1194-2010-3-2.2.patch, hive-1194-2010-3-2.patch
> If the input tables are sorted on the join key, and a mapjoin is being performed, it
is useful to exploit the sorted properties of the table.
> This can lead to substantial cpu savings - this needs to work across bucketed map joins
> Since, sorted properties of a table are not enforced currently, a new parameter can be
added to specify to use the sort-merge join.

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