Snapshot isolation and serializability compared
Research context
theory comparison · established · As of 2026-10-10
PostgreSQL 18 repeatable read uses snapshot isolation: each transaction reads a stable snapshot, but concurrent writes to different rows can produce write skew and a nonserializable joint outcome.
Key knowledge
PostgreSQL 18 repeatable read uses snapshot isolation: each transaction reads a stable snapshot, but concurrent writes to different rows can produce write skew and a nonserializable joint outcome. Its serializable level additionally tracks conflicts and may reject a transaction. Read committed can observe different committed snapshots on successive commands. These mechanisms make different performance and anomaly tradeoffs under the same workload.
Conditions and scope
- This implementation statement concerns PostgreSQL 18 as documented on 10 October 2026; SQL isolation names alone do not determine another database's mechanism.
- Serialization failures require retrying the full transaction with a suitable idempotency strategy.
Sources · 1
References
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Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: §13.2: read committed, repeatable read and serializable; anomalies, serialization failures and retries. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
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