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