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Salt the Hot Merchant

A hard Spark mock interview question on DataDriven. Practice with AI-powered feedback, real code execution, and a hire/no-hire decision.

Domain
Spark
Difficulty
hard
Seniority
mid

Interview Prompt

The daily payment reconciliation Spark job joins 1.2 billion transactions against a 500K-row merchants dimension on merchant_id. It has been failing for three days. Spark UI shows one task processing 38% of all rows while the other 199 finish in seconds. The hot merchant is your company's internal payment processor that handles all driver payouts. You cannot broadcast merchants because a downstream join adds a 2 GB enrichment table. Propose and implement a salting strategy.

How This Interview Works

  1. Read the vague prompt (just like a real interview)
  2. Ask clarifying questions to the AI interviewer
  3. Write your spark solution with real code execution
  4. Get instant feedback and a hire/no-hire decision