Super Bowl: let the timeline run late

transcript

The Super Bowl. Posts jump ten times. And the plan is to let your timeline run late. On purpose.

A normal day: about 6,000 posts a second. The big game: about 60,000 a second. Each pushed to about 700 followers. That's 42 million timeline inserts. Every second.

You know it's coming. So you pre-scale from the event calendar. Still, the posts flood in. Ten times the usual. The fan-out queues back up. Workers can't keep pace. Something has to give. So what do you protect?

The normal promise: every post in timelines within 5 seconds. Hold that now, and everyone waits on the backlog. But most people are reading, not posting. So keep reads at 99 point 99 percent. And let delivery slip to 10 to 30 seconds.

On your phone, the timeline still loads fast. It's just a little stale. The newest posts are seconds behind. Nothing fails. Then the workers catch up, and the posts land.

But here's the catch. Delay needs a limit. A fan-out queue past a million messages is the critical alarm.

A slightly stale timeline, served fast, beats making everyone wait. Degrade by delay. Not by failure.

Full breakdown in the lecture.