NOTE
PostgreSQL Isolation Levels
Read Committed, Repeatable Read, Serializable, snapshots, and serialization failures.
This is a historical learning note and may contain outdated or incomplete understanding.
PostgreSQL supports Read Committed, Repeatable Read, and Serializable semantics; READ UNCOMMITTED is treated as Read Committed. Read Committed takes a new statement snapshot, while Repeatable Read keeps a stable transaction snapshot.
Serializable adds protection against serialization anomalies using PostgreSQL’s serializable implementation and may abort transactions that must be retried. Isolation does not remove application-level uniqueness/invariant design; use constraints and retry-safe transaction logic.