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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-2847) Add support for query rewrite from the metadata
Date Sun, 23 Sep 2012 15:30:07 GMT

    [ https://issues.apache.org/jira/browse/HIVE-2847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13461442#comment-13461442
] 

Namit Jain commented on HIVE-2847:
----------------------------------

Few parameters,like hive.stats.reliable, have been introduced to figure out if stats are accurate.
The idea behind this jira is to use the stats from the metadata to rewrite some queries.

For eg: for queries like 

select count(1) from T  where ds > 10;

Say, partitions T@ds=11 and T@ds=12 satisfy the query.

If number of rows are present in the metadata for T@ds=11, T@ds=12, there is no need to scan
the data to get the results.
                
> Add support for query rewrite from the metadata
> -----------------------------------------------
>
>                 Key: HIVE-2847
>                 URL: https://issues.apache.org/jira/browse/HIVE-2847
>             Project: Hive
>          Issue Type: New Feature
>            Reporter: Namit Jain
>              Labels: gsoc, gsoc2012
>
> A simple query like: 
> select count(1) from T
> should be able to get the results from the metadata instead of scanning the complete
input table T.
> 2. the metadata only queries today does not scale to a very large number of partitions
- that needs to be fixed.

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