Run df.explain on a Parquet scan and you find ColumnarToRow, an operator whose only job is to change the data’s shape. It is the seam where two architectural eras meet, and a record of how portability in analytical systems has relocated from the JVM runtime to the data format and the query plan.
How Spark’s internal rewriting framework, Catalyst, exposes an embedded DSL with a public extension surface, the same one Delta Lake and Iceberg use to plug into the optimizer pipeline.
Six concrete anti-patterns I encountered building a real Catalyst extension: from the wrong rule type for throws, to mutable state under AQE and Spark Connect, to JVM bootstrap traps in PySpark.
Many of the most surprising performance pathologies in modern data systems are semiotic failures — structural divergences between what an interface signifies and what the underlying system does.
At 10 TB, updating 200k rows can mean rewriting thousands of files. Here’s why, and what to do about it.
Why calling Spark ’lazy’ is technically reductive, and how thinking of it as a dataflow compiler changes the way you design pipelines.