Why is the KEYS command discouraged in production?

1. A It requires admin privileges
2. ✓ B It blocks the single-threaded server while scanning the entire keyspace (correct answer)
3. C It returns only 10 results
4. D It is deprecated

Shortcut: Redis executes commands on one thread. KEYS scans every key, stalling all other traffic. SCAN iterates incrementally with a cursor and should be used instead.