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https://issues.apache.org/jira/browse/SPARK-28978?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiangrui Meng resolved SPARK-28978.
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Fix Version/s: 3.0.0
Assignee: Bago Amirbekian
Resolution: Fixed
> PySpark: Can't pass more than 256 arguments to a UDF
> ----------------------------------------------------
>
> Key: SPARK-28978
> URL: https://issues.apache.org/jira/browse/SPARK-28978
> Project: Spark
> Issue Type: Bug
> Components: PySpark
> Affects Versions: 2.3.2, 2.4.0, 2.4.4
> Reporter: Jim Fulton
> Assignee: Bago Amirbekian
> Priority: Major
> Labels: koalas, mlflow, pyspark
> Fix For: 3.0.0
>
>
> This code:
> [https://github.com/apache/spark/blob/712874fa0937f0784f47740b127c3bab20da8569/python/pyspark/worker.py#L367-L379]
> Creates Python lambdas that call UDF functions passing arguments singly,
> rather than using varargs. For example: `lambda a: f(a[0], a[1], ...)`.
> This fails when there are more than 256 arguments.
> mlflow, when generating model predictions, uses an argument for each feature
> column. I have a model with > 500 features.
> I was able to easily hack around this by changing the generated lambdas to
> use varargs, as in `lambda a: f(*a)`.
> IDK why these lambdas were created the way they were. Using varargs is much
> simpler and works fine in my testing.
>
>
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