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From "John Sichi (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-2470) Improve support for Constant Object Inspectors
Date Wed, 28 Sep 2011 18:54:45 GMT

    [ https://issues.apache.org/jira/browse/HIVE-2470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13116691#comment-13116691
] 

John Sichi commented on HIVE-2470:
----------------------------------

Cool stuff.  But one question:  do we actually need to change UDF's to make them foldable?
 Another way I've seen this done in the past is for the optimizer to actually figure out the
maximum constant subexpression (similar to what we already do for figuring out deterministic
expressions during predicate pushdown), and then evaluate that and replace the expression
with the constant result (and then carry on with optimization).  The benefit is that then
other parts of the optimizer see the constant instead of the complex expression.  For example,
index search wants to see COL=CONSTANT, not COL=COMPLEX_EXPRESSION.
                
> Improve support for Constant Object Inspectors
> ----------------------------------------------
>
>                 Key: HIVE-2470
>                 URL: https://issues.apache.org/jira/browse/HIVE-2470
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Jonathan Chang
>            Assignee: Jonathan Chang
>         Attachments: HIVE-1360.part2.patch, HIVE-2470.patch
>
>
> ConstantObjectInspectors are nice but they need to be more widely supported and used.
 In particular,
> * More functions need to be using them.
> * There need to be facilities for propagating constness.
> * Support for complex types must be added.

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