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