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From "Vikram Dixit K (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HIVE-3652) Join optimization for star schema
Date Wed, 13 Feb 2013 00:29:12 GMT

     [ https://issues.apache.org/jira/browse/HIVE-3652?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Vikram Dixit K resolved HIVE-3652.
----------------------------------

       Resolution: Duplicate
    Fix Version/s: 0.11.0

The work required for this jira is fixed as part of de-emphasizing of map-join work done in
HIVE-3784. The query 

{format}select /*+ MAPJOIN(b,c) */ from FACT a join DIM1 b on a.k1=b.k1 JOIN DIM2 c on b.k2=c.k2{format}

runs in 1 MR job (based on the noConditionalTask.size).
                
> 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: Vikram Dixit K
>             Fix For: 0.11.0
>
>
> 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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