Ed Elliott uncovers a mystery:
To understand this we need to take a look at how we can create a UDF in .NET that is called by the Java VM Apache Spark code because, that is logically, what happens. In our application we call into Apache Spark and ask it to do things like read from a file, run some transformation and write files back out again. With UDF’s, we ask Spark to run a UDF and Spark comes back to our UDF, passing it some data and asks the UDF to execute but the Java VM does not understand how to execute .NET code.
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