Notes and explanations about software engineering.
A deep dive into pages, slotted pages, heap files, and full table scans — the physical layer underneath every SQL query we write.
A ground-up tour of MVCC in PostgreSQL — row versions, the hidden columns and how a tuple is really laid out on disk, snapshots, and the visibility rule — and how they let thousands of transactions read and write at once without waiting on each other.
MVCC leaves a dead row version behind on every update. This is the cleanup story — why bloat slows queries down instead of just filling disk, what VACUUM and VACUUM FULL really do, how autovacuum decides when to run, why one forgotten transaction can block cleanup across the whole database, and how freezing stops 32-bit transaction IDs from silently eating your data.