tag: pipeline

Fifteen years of building products leave you with scars, and ours all share an origin: data that entered a system through more than one door. This is the story of why Kilden only has one.

Who decides which users see your new feature? In Kilden, a hash function — with no memory, no assignment table, and no way to disagree with itself. And because flags sit on an event pipeline, they can target behavior, not just attributes.

For a while, some of our session replays played back as minutes of black screen. The recordings were fine. The bug was in a filename — and the fix is a rule about key design worth stealing.

Your analytics tool and your email tool disagree about what a user did today. Only one of them is wrong — good luck finding out which. Kilden's answer is structural: four products that physically cannot disagree, because they read the same stream.

Ask a queue vendor for exactly-once delivery and watch the asterisks multiply. It doesn't exist — but exactly-once effects do, and the whole trick is three decisions about where duplicates go to die.