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A key chooses one drawer.

Why can an index skip most records?

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The original inspiration

Levers & fulcrums The surprising gyroscope The field cannon Inside the human body

Original demonstrations by The Bugged Dev. The teaching models and interactions here are new implementations.

Community builds

New teaching models inspired by public builds shared around Anatomy.

Anatomy · the original announcement How a rocket pushes through space · Gustavo Inside a tactile key switch · @retaqib Pressure through the coffee bed · Gustavo The overbalance wheel · Shawn A seconds pendulum clock · @Baconbrix Three feet on the ground · Soju Inside a layered particle detector · Yash A double-deck pressure cabin · Charlie Leave the spent booster behind · @quantapar Principal, interest and escrow · Sean Gear a Martian year · @samani_Two balls in, two balls out · @samani_Two slits, one probability pattern · @samani_Join through a clear plastic cover · Josh Brown Lay pipe without a sharp bend · @Phi10w Eight cylinders and a blower · @love4hxns Four columns under a Joglo roof · Nur Asyrof An office for dependent tasks · Yaroslav Yablonski One image, six editable layers · Meng To The Redis caching machine · @uviii_03 Inside the Sony CMD-J5 · Ann Afterburner thrust stand · Joshua Guo Open-back headphones · Surajan Shrestha Two-thread lockstitch machine · @slashui Signal factory · Dhruval Golakiya

Computers and networks

A key chooses one drawer.

Why can an index skip most records?

Setting up the mechanism…

Record payload: No current query

More

Key comparisons: 0
Record pages scanned: 0
Full-scan comparisons: 14

Fit the rack, leaf drawers and records.

Why can an index skip most records?

A balanced search tree uses separators to choose a small leaf page. In this cabinet, any key needs one root and one leaf page; the full scan examines records until it finds a match or reaches the end. Missing keys return no record. The counts describe this fixed tree, not a universal database speedup.

Key 14: 3 separator comparisons + 2 leaf comparisons = 5

What this model simplifies

A fixed balanced two-level B+ tree over keys 1–16, with root separators 5, 9 and 13 and four leaves of four keys. Leaf records contain payload key × 10 + 3. Separator and leaf searches are explicitly linear within each page. Page reads and key comparisons are separate counts. This teaching cabinet is not a running PostgreSQL database; heap fetches, MVCC, cache state and mutations are omitted.

Read the source · postgresql.org ↗

Put it to work.

Find key 14 through two index pages using fewer comparisons than a full scan.

Make it work.

Compare indexed lookup with a full scan.

Run

Fine adjustments 1

Lookup key