What is data skew in a distributed job (Spark), and how do you fix it?
The number-one cause of mysteriously slow Spark jobs: one partition handles most of the work while the rest idle. The signal is reading the symptom (a few straggler tasks) and reaching for the right fix, salting, broadcast, or AQE.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
The number-one cause of mysteriously slow Spark jobs: one partition handles most of the work while the rest idle. The signal is reading the symptom (a few straggler tasks) and reaching for the right fix, salting, broadcast, or AQE.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
