Transactions and Concurrency

A transaction is a group of statements that succeed or fail together. Concurrency is what happens when more than one transaction runs at the same time. The intersection — what guarantees you get, what anomalies you don't — is one of the most consequential and least-understood areas of SQL.

Place in the curriculum

• Prerequisites: Data Manipulation for BEGIN/COMMIT/ROLLBACK. Some familiarity with Indexes helps for the locking discussion.

Chapters

1. ACID and Transactions — Atomicity, Consistency, Isolation, Durability. What each means in practice.
2. Isolation Levels — the four standard levels, the anomalies they prevent, snapshot vs serializable.
3. MVCC and Locking — Postgres's MVCC mental model, row vs table locks, deadlocks, advisory locks.