Lazy Evaluation in PySpark: Why Spark Waits, How It Optimizes, and When Your Code Actually Runs
Master lazy evaluation — the most important PySpark concept nobody explains properly. Why Spark waits, how the Catalyst Optimizer rewrites your code, transformations vs actions with complete lists, predicate pushdown, column pruning, the DAG, narrow vs wide transformations, the cache trap, proving laziness with a hands-on experiment, and how it powers your SCD Type 2 pipeline.