PostgreSQL Subtransactions Considered Harmful | Database Lab · Fast clones of PostgreSQL databases · Postgres.aiPostgreSQL subtransactions (nested transactions) may cause multiple performance and scalability issues: higher rates of XID growth and higher risks of transaction ID wraparound, performance degradation when more than PGPROC_MAX_CACHED_SUBXIDS (64) are used in a session, drastic performance slowdowns when subtransactions are combined with SELECT .. FOR UPDATE, and finally, brief downtime on standbys when subtranasctions used on the primary in paralell with long-running transactions or just slow statements. Subtransactions can be created using SAVEPOINT in regular SQL or using EXCEPTION WHEN blocks in PL/pgSQL. 