This dark store closes at 15 minutes of backlog, and reopens only under 8

transcript

This dark store closes when its backlog passes 15 minutes. It won't reopen until the backlog is under 8. Why not 15?

First, it's not an on-off switch. The mode is set every few seconds. Backlog over 4 minutes, or riders short? Stretched. Estimates grow. Every order still accepted. Over 8, or promises kept under 85 percent? Throttled. Outer cells close first. Over 15, or power or network lost? Closed. Not serviceable right now.

Stretching is the cheapest rung. Everyone still gets served, with honest estimates. When it must shed, outer cells go first. Their long rides cost the most rider minutes.

Now the way back. Reopen at the same 15? Then the store flaps open and shut every 30 seconds. So close at 15. But reopen only under 8. And only after 5 minutes down there. That gap is called hysteresis.

Every rung works this way. Stretched at 4 minutes of backlog. Back under 2. Throttled at 8. Back under 5. Closed at 15. Back under 8, and the store healthy.

One threshold, both ways, makes a system flap. Two thresholds and a wait make it calm. Close at 15. Open at 8.

Full breakdown in the lecture.