Assess graduate-level understanding of database concurrency control: principles and trade-offs of locking protocols (two‑phase locking variants, deadlock handling, lock granularity and compatibility), multiversion concurrency control mechanisms (versioning, timestamp ordering, visibility rules, garbage collection), and snapshot isolation semantics (how snapshots are taken, allowed anomalies such as write skew, and its relation to serializability). Include short analyses of execution histories and design/trade-off reasoning.