Diagnosing and tuning PostgreSQL 17/18 from engine evidence: MVCC tuple versions, VACUUM/freeze and bloat, HOT updates and visibility maps, plans and cardinality, work memory/spills, WAL and checkpoints, locks/SSI, connection processes and PgBouncer session semantics, plus pgjdbc prepared-plan, batch, and fetch behavior. Use when the symptom or change depends on PostgreSQL internals. Not generic query-plan, ORM, or HikariCP sizing guidance.
