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From "Gunther Hagleitner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-7506) MetadataUpdater: provide a mechanism to edit the statistics of a column in a table (or a partition of a table)
Date Wed, 30 Jul 2014 22:55:39 GMT

    [ https://issues.apache.org/jira/browse/HIVE-7506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14080125#comment-14080125
] 

Gunther Hagleitner commented on HIVE-7506:
------------------------------------------

[~damien.carol] I think the use for this is different that analyze. The ability to update
certain stats without scanning any data or without "hacking the backend db" is useful in a
number of cases. It helps (esp for CBO work) to set up unit tests quickly and verify both
cbo and the stats subsystem. It also helps when experimenting with the system if you're just
trying out hive/hadoop on a small cluster. Finally it gives you a quick and clean way to fix
things when something went wrong wrt stats in your environment.

> MetadataUpdater: provide a mechanism to edit the statistics of a column in a table (or
a partition of a table)
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-7506
>                 URL: https://issues.apache.org/jira/browse/HIVE-7506
>             Project: Hive
>          Issue Type: New Feature
>          Components: Database/Schema
>            Reporter: pengcheng xiong
>            Assignee: pengcheng xiong
>            Priority: Minor
>   Original Estimate: 252h
>  Remaining Estimate: 252h
>
> Two motivations:
> (1) CBO depends heavily on the statistics of a column in a table (or a partition of a
table). If we would like to test whether CBO chooses the best plan under different statistics,
it would be time consuming if we load the whole table and create the statistics from ground
up.
> (2) As database runs,  the statistics of a column in a table (or a partition of a table)
may change. We need a way or a mechanism to synchronize. 
> We propose the following command to achieve that:
> ALTER TABLE table_name PARTITION partition_spec [COLUMN col_name] UPDATE STATISTICS col_statistics
[COMMENT col_comment]



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