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From "Mark Grover (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3652) Join optimization for star schema
Date Sun, 04 Nov 2012 20:02:13 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13490286#comment-13490286
] 

Mark Grover commented on HIVE-3652:
-----------------------------------

Amareshwari, what are your thoughts on how the user can specify which is a fact table and
which is a dimension table? Or, are you using storage based statistics to infer that information?
                
> Join optimization for star schema
> ---------------------------------
>
>                 Key: HIVE-3652
>                 URL: https://issues.apache.org/jira/browse/HIVE-3652
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Amareshwari Sriramadasu
>            Assignee: Amareshwari Sriramadasu
>
> Currently, if we join one fact table with multiple dimension tables, it results in multiple
mapreduce jobs for each join with dimension table, because join would be on different keys
for each dimension. 
> Usually all the dimension tables will be small and can fit into memory and so map-side
join can used to join with fact table.
> In this issue I want to look at optimizing such query to generate single mapreduce job
sothat mapper loads dimension tables into memory and joins with fact table on different keys
as well.

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