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From "Prasad Chakka (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-279) Implement predicate push down for hive queries
Date Sat, 28 Mar 2009 01:24:50 GMT

    [ https://issues.apache.org/jira/browse/HIVE-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12690161#action_12690161
] 

Prasad Chakka commented on HIVE-279:
------------------------------------

will add the tests & take care of minor comments

colExprMap & posToAliasMap are just like any other transient fields in the operator and
not needed beyond predicate pushdown. so i am going to leave them there.

TableScan operator can't have more than one child or rather any children of TableScan can't
have more than one parent. So changing the order doesn't matter and this is assumed in lot
of places. But I will change it so that the order is unchanged.



> Implement predicate push down for hive queries
> ----------------------------------------------
>
>                 Key: HIVE-279
>                 URL: https://issues.apache.org/jira/browse/HIVE-279
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>    Affects Versions: 0.2.0
>            Reporter: Prasad Chakka
>            Assignee: Prasad Chakka
>         Attachments: hive-279.2.patch, hive-279.3.patch, hive-279.4.patch, hive-279.patch
>
>
> Push predicates that are expressed in outer queries into inner queries where possible
so that rows will get filtered out sooner.
> eg.
> select a.*, b.* from a join b on (a.uid = b.uid) where a.age = 20 and a.gender = 'm'
> current compiler generates the filter predicate in the reducer after the join so all
the rows have to be passed from mapper to reducer. by pushing the filter predicate to the
mapper, query performance should improve.

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