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From "Steven Phillips (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (DRILL-3912) Common subexpression elimination
Date Wed, 07 Oct 2015 21:43:26 GMT

     [ https://issues.apache.org/jira/browse/DRILL-3912?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Steven Phillips reassigned DRILL-3912:
--------------------------------------

    Assignee: Steven Phillips

> Common subexpression elimination
> --------------------------------
>
>                 Key: DRILL-3912
>                 URL: https://issues.apache.org/jira/browse/DRILL-3912
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Steven Phillips
>            Assignee: Steven Phillips
>
> Drill currently will evaluate the full expression tree, even if there are redundant subtrees.
Many of these redundant evaluations can be eliminated by reusing the results from previously
evaluated expression trees.
> For example,
> {code}
> select a + 1, (a + 1)* (a - 1) from t
> {code}
> Will compute the entire (a + 1) expression twice. With CSE, it will only be evaluated
once.
> The benefit will be reducing the work done when evaluating expressions, as well as reducing
the amount of code that is generated, which could also lead to better JIT optimization.



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