The Slate, Properly (caching to real depth)

The slate drawn again with the engineering on it: what a copy is worth, what makes it lie, and the failure that takes the stall down.

Before you start. You need one picture from The slate next to the stove (caching): the chai stall chalks the day’s prices on a slate by the stove, so nobody walks to the register in the back room for an answer somebody already fetched. That is the whole background. The rest is a programmer at LiveJournal in 2003, a team at Facebook in 2013, one table you add up by hand, and a failure that strikes when everything is going well.