**Why it matters**: At scale, design choices directly impact reliability, latency, and cost. Wrong decisions compound across jobs and teams.
Adaptive Query Execution (AQE) optimizes Spark queries at runtime. Introduced in Spark 3.x, it: (1) Coalesces partitions after shuffle based on actual data sizes (`spark.sql.adaptive.coalescePartitions.enabled`). (2) Converts Sort-Merge Join to Broadcast Join when runtime stats show a join side is small....
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like Globant. The answer also includes follow-up discussion points that interviewers commonly explore.
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