Amazon RDS for PostgreSQL Multi-AZ Clusters Fail Snapshot Isolation
2025-04-29
Jepsen's testing reveals that Amazon RDS for PostgreSQL multi-AZ clusters don't fully guarantee snapshot isolation. Anomalies like G-nonadjacent cycles, violating snapshot isolation rules, were observed. These included Long Fork, suggesting RDS for PostgreSQL might offer the weaker Parallel Snapshot Isolation. This means read transactions may disagree on execution order under high concurrency. Users should be mindful of transaction structures, avoid Long Fork, or use only the writer endpoint to recover snapshot isolation.