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What is data skew in a distributed job (Spark), and how do you fix it?

The top cause of mysteriously slow Spark jobs: one partition does 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 Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

The top cause of mysteriously slow Spark jobs: one partition does 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.

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