[jira] [Commented] (SPARK-26182) Cost increases when optimizing scalaUDF

["Jiayi Liao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-26182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16704347#comment-16704347 ] 

Jiayi Liao commented on SPARK-26182:
------------------------------------

[~fanweiwen] We're doing some optimizations on our own streaming business. I'm appreciate if you're able to tell me the reason for this.

> Cost increases when optimizing scalaUDF
> ---------------------------------------
>
>                 Key: SPARK-26182
>                 URL: https://issues.apache.org/jira/browse/SPARK-26182
>             Project: Spark
>          Issue Type: Bug
>          Components: Optimizer
>    Affects Versions: 2.4.0
>            Reporter: Jiayi Liao
>            Priority: Major
>
> Let's assume that we have a udf called splitUDF which outputs a map data.
>  The SQL
> {code:java}
> select
>     g['a'], g['b']
> from
>    ( select splitUDF(x) as g from table) tbl
> {code}
> will be optimized to the same logical plan of
> {code:java}
> select splitUDF(x)['a'], splitUDF(x)['b'] from table
> {code}
> which means that the splitUDF is executed twice instead of once.
> The optimization is from CollapseProject. 
>  I'm not sure whether this is a bug or not. Please tell me if I was wrong about this.



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