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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-364) Hive Operators should calculate the value of common expressions just once
Date Tue, 24 Mar 2009 20:59:50 GMT

    [ https://issues.apache.org/jira/browse/HIVE-364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12688865#action_12688865
] 

Zheng Shao commented on HIVE-364:
---------------------------------

Note that if an expression contains functions like rand(), it should not be shared and should
be calculated separately.


> Hive Operators should calculate the value of common expressions just once
> -------------------------------------------------------------------------
>
>                 Key: HIVE-364
>                 URL: https://issues.apache.org/jira/browse/HIVE-364
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Serializers/Deserializers
>            Reporter: Zheng Shao
>
> Currently, if we have "t.a + t.b" in 2 different expressions in the select clause / where
clause, we are computing it twice.
> We should cache the value of the expression evaluation result to save CPU time.

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