snapshot-isolation · shipping · also SI

Snapshot isolation

Snapshot isolation gives a transaction a stable committed snapshot plus its own writes and prevents concurrent transactions that write the same data from both committing.

It can permit write skew across different rows. PostgreSQL 18 uses this model for Repeatable Read, not its stronger Serializable level. A transaction snapshot is an isolation mechanism, not a storage backup.

Relations

related

serializability, write-skew

Citations

1. Hal Berenson et al. A Critique of ANSI SQL Isolation Levels. ACM SIGMOD 1995; MSR-TR-95-51, section 4.2. (accessed 2026-10-12)
2. PostgreSQL 18 documentation, section 13.2: Transaction Isolation. (accessed 2026-10-12)
3. Storage consistency: ordering is not a transaction or a durability promise (accessed 2026-10-12)

JSON: /data/terms/snapshot-isolation.json