Postgresql Vacuum Beauty

The Day I Realized PostgreSQL Vacuum Was Actually Beautiful

At Atlassian, we had this one database that everyone called “the beast” - a 40TB PostgreSQL instance that stored every git commit hash for Bitbucket Cloud. For months, I thought vacuum was just this annoying maintenance thing that made queries slow at random times. Then I spent a weekend actually reading the source code, and my mind was completely blown by the elegance of MVCC’s garbage collection.

The beauty is in how PostgreSQL handles dead tuples like a crime scene investigator. Every row has this hidden system column called xmin and xmax that tracks transaction visibility, and vacuum is basically CSI PostgreSQL, figuring out which versions of reality can safely be forgotten. When you delete a row, PostgreSQL doesn’t actually delete it - it just marks it as dead and waits for vacuum to come clean up the body. This is why your table can be 90% dead tuples and still technically work, like a zombie database shambling along.

What really gets me is how autovacuum uses the visibility map to skip pages that don’t need cleaning, like a smart janitor who knows which rooms haven’t been used. I started treating vacuum tuning like audio mixing - you need just enough aggressive cleaning to prevent bloat, but not so much that you’re constantly fighting for I/O with your actual queries. Once you understand that vacuum is really about managing parallel universes of data, the whole thing becomes almost poetic.