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https://issues.apache.org/jira/browse/DRILL-346?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13881498#comment-13881498
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Jinfeng Ni commented on DRILL-346:
----------------------------------
review board link:
https://reviews.apache.org/r/17333/
> Runtime generated code should evaluate constant expression once in doSetup
> method
> ---------------------------------------------------------------------------------
>
> Key: DRILL-346
> URL: https://issues.apache.org/jira/browse/DRILL-346
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Jinfeng Ni
> Assignee: Jinfeng Ni
> Attachments: DRILL_346.1.patch.txt
>
>
> Currently, when runtime CodeGenerator logic generates class to evaluate an
> expression, it would put the code in doEval() method, regardless of whether
> the expression is a constant, or part of the expression is a constant. This
> means the generated code for the constant expression will be executed once
> for every record, in stead of once for each record batch.
> For a constant expression, we should put the code in doSetup() method, so
> that it will be executed once per record batch. Doing so would improve
> runtime code efficiency.
> In addition, for some function call expression, if the arguments are
> constant, we may want to refer to the constant arguments in doSetup(). For
> instance, given function : regexp_replae(input_string, regex, replace), if
> regex is a constant (eg : regexp_replace(varcharcol, "a[bc]", "XYZ") ), the
> implementation of regexp_replace would use the constant to build a
> java.Pattern in doSetup(), and repeatedly use that java.Pattern object in
> doEval() for each record. This requires CodeGenerator to make the constant
> arguments accessible to doSetup() method for function call.
>
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