New Day 12: Udf Vs Pandas Udf 2025

Welcome to Day 12 of the Spark Mastery Series! Today we dissect a topic that has ruined the performance of countless ETL pipelines:

A UDF seems innocent - but adding one UDF can slow your entire job by 10x.

Let’s understand why and how to avoid that with better alternatives.

A UDF (User Defined Function) is a Python function applied on Spark DataFrame.

Every record goes through Python → JVM boundary → slow.

If Spark has a built-in function → NEVER write a UDF.

🌟 3. Pandas UDF — The Best Alternative to Normal UDFs

Pandas UDF = uses Apache Arrow for vectorized operations → much faster.

Spark sends data in batches, not row-by-row → huge speed improvement.

🟢 Scalar Pandas UDF Operates like built-in function.

Source: Dev.to