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https://issues.apache.org/jira/browse/IMPALA-6590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16764269#comment-16764269
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Paul Rogers commented on IMPALA-6590:
-------------------------------------
We are working on steps to improve expression rewrites. The goal is to merge
rewrites into expression analysis to achieve a number of benefits, including
avoiding the costly pattern matching steps currently used in rewrites. Will
also allow better type propagation, avoidance of the need to analyze, reset and
re-analyze, etc. See IMPALA-8041 for some of the changes.
> Disable expr rewrites and codegen for VALUES() statements
> ---------------------------------------------------------
>
> Key: IMPALA-6590
> URL: https://issues.apache.org/jira/browse/IMPALA-6590
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 2.8.0, Impala 2.9.0, Impala 2.10.0, Impala 2.11.0
> Reporter: Alexander Behm
> Priority: Major
> Labels: perf, planner, ramp-up, regression
>
> The analysis of statements with big VALUES clauses like INSERT INTO <tbl>
> VALUES is slow due to expression rewrites like constant folding. The
> performance of such statements has regressed since the introduction of expr
> rewrites and constant folding in IMPALA-1788.
> We should skip expr rewrites for VALUES altogether since it mostly provides
> no benefit but can have a large overhead due to evaluation of expressions in
> the backend (constant folding). These expressions are ultimately evaluated
> and materialized in the backend anyway, so there's no point in folding them
> during analysis.
> Similarly, there is no point in doing codegen for these exprs in the backend
> union node.
> *Workaround*
> {code}
> SET ENABLE_EXPR_REWRITES=FALSE;
> SET DISABLE_CODEGEN=TRUE;
> {code}
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