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From "Jinfeng Ni (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4715) Java compilation error for a query with large number of expressions
Date Fri, 10 Jun 2016 19:55:21 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15325176#comment-15325176

Jinfeng Ni commented on DRILL-4715:

AFAIK, it's not caused by lacking support of subexpression level. It's block vs expressions.
 In Aditya's work, the breakup happens at block level, assuming each expression will go into
a separate block.  CSE puts all the expressions for some operators (project,) into one block.
That essentially disable Aditya's checking, since the method will have only one block.

[1] https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/expr/ClassGenerator.java#L222-L226
[2] https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/expr/ClassGenerator.java#L254

> Java compilation error for a query with large number of expressions
> -------------------------------------------------------------------
>                 Key: DRILL-4715
>                 URL: https://issues.apache.org/jira/browse/DRILL-4715
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Execution - Codegen
>            Reporter: Jinfeng Ni
> The following query would hit compilation error, when Drill generates and compiles the
run-time code. 
> Q1 :
> {code}
> select  expr1, expr2, expr3, ...., exprN
> from table
> {code} 
> In Q1, expr1, expr2, ..., exprN are non-trivial expression (in stead of simply column
reference), and N is big enough, then the run-time generated code may have a method which
goes beyond the 64k limit imposed by JVM. 
> This seems to be a regression from DRILL-3912 (Common subexpression elimination). CSE
tries to put as many expressions in one block as possible, to detect and eliminate as many
CSE as possible. However, this implies we may end up with big method with compilation error.

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