PostgreSQL Fundamentals

PostgreSQL is a mature, open-source relational database, and it's a deep subject because its advanced features — not just 'it runs SQL' — are what decide whether a Spring Boot app is fast and correct under real load. The capabilities I anchor on: MVCC, multi-version concurrency control, which lets readers not block writers by giving each transaction a snapshot, enabling high concurrency at the cost of bloat that VACUUM reclaims. The index types — B-tree for equality and range, GIN for arrays and JSONB and full-text, GiST for geospatial — because choosing the right index is the core tuning lever. JSONB, which gives you a queryable, indexable document model inside Postgres as a middle ground for semi-structured fields. EXPLAIN ANALYZE, which shows the actual query plan, because reading the plan rather than guessing is how you find slow queries. And isolation levels, which trade consistency for concurrency — read committed is the fast default, serializable is correct for things like account transfers but throws serialization failures you must retry. The trade-off I always name is performance versus correctness, and the cost of indexes: they speed up reads but slow writes and consume space, so I index only what queries actually need.