Database transactions guarantee the fundamental ACID properties (Atomicity, Consistency, Isolation, Durability) that enable reliable business applications. However, the “I” in ACID (Isolation) is almost never absolute in production databases.
To maintain high transaction throughput across concurrent connections, storage engines offer a spectrum of isolation levels. Operating at the wrong isolation level can introduce subtle, catastrophic data corruption bugs: phantom inventory, race conditions during bank account transfers, and classic Write Skew anomalies that pass individual database constraints while violating global invariants.
This module deconstructs transaction isolation internals: the ANSI SQL isolation hierarchy, Multi-Version Concurrency Control (MVCC) snapshot visibility engines in PostgreSQL and MySQL InnoDB, Strict Two-Phase Locking (SS2PL), and modern Serializable Snapshot Isolation (SSI).