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https://issues.apache.org/jira/browse/HIVE-5771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13824147#comment-13824147
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Eric Hanson commented on HIVE-5771:
-----------------------------------
Right now, a query like this:
select ...
from T
where a = 2 * 2;
will not vectorize. This is because the "=(column,scalar)" operator looks in
the syntax tree to find variable expression result or column on the left and a
single scalar on the right. If the constant folder can turn 2 * 2 into the
integer literal 4, then the vectorization code can process the "a = 4" filter.
Being able to fold CAST(constant-expression AS type) will also help, because
people use this, especially for casting a string literal to a timestamp.
> Constant propagation optimizer for Hive
> ---------------------------------------
>
> Key: HIVE-5771
> URL: https://issues.apache.org/jira/browse/HIVE-5771
> Project: Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Ted Xu
> Assignee: Ted Xu
> Attachments: HIVE-5771.patch
>
>
> Currently there is no constant folding/propagation optimizer, all expressions
> are evaluated at runtime.
> HIVE-2470 did a great job on evaluating constants on UDF initializing phase,
> however, it is still a runtime evaluation and it doesn't propagate constants
> from a subquery to outside.
> It may reduce I/O and accelerate process if we introduce such an optimizer.
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