[jira] [Commented] (SPARK-45745) Extremely slow execution of sum of columns in Spark 3.4.1

["Javier (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-45745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17781539#comment-17781539 ] 

Javier commented on SPARK-45745:
--------------------------------

I originally posted a comment in StackOverflow asking for feedback on this ([https://stackoverflow.com/questions/77391731/extremely-slow-execution-in-spark-3-4-1-when-computing-the-sum-of-pyspark-datafr]) and a user there pointed me to a problem to a never ending UT reported here https://issues.apache.org/jira/browse/SPARK-43972 It is for the same Spark version, but I honestly don't know if this can be related.

> Extremely slow execution of sum of columns in Spark 3.4.1
> ---------------------------------------------------------
>
>                 Key: SPARK-45745
>                 URL: https://issues.apache.org/jira/browse/SPARK-45745
>             Project: Spark
>          Issue Type: Bug
>          Components: PySpark
>    Affects Versions: 3.4.1
>            Reporter: Javier
>            Priority: Major
>
> We are in the process of upgrading some pySpark jobs from Spark 3.1.2 to Spark 3.4.1 and some code that was running fine is now basically never ending even for small dataframes.
> We have simplified the problematic piece of code and the minimum pySpark example below shows the issue:
> {code:java}
> n_cols = 50
> data = [{f"col{i}": i for i in range(n_cols)} for _ in range(5)]
> df_data = sql_context.createDataFrame(data)
> df_data = df_data.withColumn(
>     "col_sum", sum([F.col(f"col{i}") for i in range(n_cols)])
> )
> df_data.show(10, False) {code}
> Basically, this code with Spark 3.1.2 runs fine but with 3.4.1 the computation time seems to explode when the value of `n_cols` is bigger than about 25 columns. A colleague suggested that it could be related to the limit of 22 elements in a tuple in Scala 2.13, since the 25 columns are suspiciously close to this. Is there any known defect in the logical plan optimization in 3.4.1? Or is this kind of operations (sum of multiple columns) supposed to be implemented differently?



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