[BLCCoreStudio]

Summary

Upgrades database/postgresql from a compact schema-v1 overview into a schema-v3 deep technical reference centered on PostgreSQL's real execution and storage lifecycle: server processes, planner/executor, MVCC snapshots, locks, WAL, checkpoints, vacuum, indexes, replication, backup, recovery, and security.

Changes

• explain cluster/database/schema/process architecture and connection lifecycle
• deepen parser/planner/executor flow, planner statistics, ANALYZE, EXPLAIN, and row-estimate diagnosis
• cover MVCC tuple versions, snapshots, isolation levels, retries, locks, deadlocks, advisory locks, HOT, visibility map, vacuum/autovacuum, and transaction-ID aging
• document WAL durability, checkpoints, memory/concurrency capacity, index families, partitioning, JSONB, extensions, and production DDL/migration safety
• add physical/logical backup, PITR, streaming/synchronous replication, slots, hot-standby conflicts, logical replication, HA/fencing, and restore verification
• cover roles, pg_hba.conf, TLS, RLS, search-path/security-definer boundaries, connection storms/pooling, monitoring, incident triage, failure modes, and upgrade discipline
• verify the canonical PostgreSQL license and add Technology Universe coverage plus typed alternatives to MySQL and SQLite

Quality bar

The module treats PostgreSQL as an MVCC/WAL database system with operational state, not merely a SQL feature list. It makes transaction visibility, maintenance, planner estimates, WAL/replication retention, backup recovery, and HA/security boundaries explicit enough to reason about production failures.