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PostgreSQL: Documentation: 16: 13.2. Transaction Isolation

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The SQL standard defines four levels of transaction isolation. The most strict is Serializable, which is defined by the standard in a paragraph which says that any concurrent execution of a set of Serializable transactions is guaranteed to produce the same effect as running them one at a time in some order. The other three levels are defined in terms of phenomena, resulting from interaction between concurrent transactions, which must not occur at each level. The standard notes that due to the definition of Serializable, none of these phenomena are possible at that level. (This is hardly surprising -- if the effect of the transactions must be consistent with having been run one at a time, how could you see any phenomena caused by interactions?) The phenomena which are prohibited at various levels are: A transaction reads data written by a concurrent uncommitted transaction. A transaction re-reads data it has previously read and finds that data has been modified by another transaction (t

PostgreSQL: Documentation: 18: 13.2. Transaction Isolation July 16, 2026: PostgreSQL 19 Beta 2 Released! Documentation → PostgreSQL 18 Supported Versions: Current ( 18 ) / 17 / 16 / 15 / 14 Development Versions: 19 / devel Unsupported versions: 13 / 12 / 11 / 10 / 9.6 / 9.5 / 9.4 / 9.3 / 9.2 / 9.1 / 9.0 / 8.4 / 8.3 / 8.2 / 8.1 / 8.0 / 7.4 / 7.3 / 7.2 / 7.1 13.2. Transaction Isolation Prev Up Chapter 13. Concurrency Control Home Next 13.2. Transaction Isolation # 13.2.1. Read Committed Isolation Level 13.2.2. Repeatable Read Isolation Level 13.2.3. Serializable Isolation Level The SQL stan

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