A Cosmos DB query runs without the partition key. What is the performance impact?
- A Query is rejected
- B Query runs as a cross-partition fan-out, consuming more RUs (correct answer)
- C Query uses a secondary index automatically
- D No impact; Cosmos DB optimizes all queries
Shortcut: Cross-partition queries fan out to every partition, multiplying RU cost. Always include the partition key in queries where possible for single-partition (efficient) execution.