A detailed technical examination of Azure Database for PostgreSQL Flexible Server, the fifth in a series reviewing managed PostgreSQL offerings. The central architectural distinction is that Flexible Server implements HA via synchronous PostgreSQL streaming replication at the database-process level — every commit waits for WAL to be flushed on both primary and standby — unlike competitors that use block-level storage replication. This design provides strong, auditable durability guarantees but puts the standby directly in the write path, meaning standby degradation raises primary commit latency. Key operational insights include: the SyncRep wait event as the diagnostic tell for standby-induced stalls, the counterintuitive behavior that cancelling a stuck COMMIT still commits the transaction, and that blast radius scales with commit frequency not size. The post also covers same-zone vs. zone-redundant HA tradeoffs, built-in PgBouncer, extension allow-list constraints, the burstable tier's production hazards, and best-fit workload profiles.
