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LetsGit.IT / Categories / PostgreSQL Answer VACUUM removes dead tuples left by MVCC , updates visibility maps and statistics, and helps prevent table bloat and transaction ID wraparound. Autovacuum runs this automatically in the background so the database stays healthy.
Advanced answer Deep dive Expanding on the short answer — what usually matters in practice:
Context (tags): vacuum, autovacuum, maintenance, mvcc Data model and access patterns: dominant queries (read/write ratio, sorting, pagination). Indexes: when they help vs hurt (write amplification, memory). Consistency & transactions: what’s guaranteed and what can bite you. Explain the "why", not just the "what" (intuition + consequences). Trade-offs: what you gain/lose (time, memory, complexity, risk). Edge cases: empty inputs, large inputs, invalid inputs, concurrency. Examples A tiny example (query shape):
-- Example: index + query shape
SELECT *
FROM users
WHERE email = '[email protected] '
LIMIT 1;Common pitfalls Too generic: no concrete trade-offs or examples. Mixing average-case and worst-case (e.g., complexity). Ignoring constraints: memory, concurrency, network/disk costs. Interview follow-ups When would you choose an alternative and why? What production issues show up and how do you diagnose them? How would you test edge cases? in Postgres: why don’t readers block writers?
#postgres #mvcc #concurrency