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