R7Cold caches and thundering herds

The problem

1 s on screen = 100 ms

Only the cache restarted. Why did the whole site go down?

Back up, and empty

A cache holds the 800 most asked-for of 3,000 pages, in front of a database that answers 80 a second at most.

Live metrics for each version of the scene
Metric	Cold restart	Warmed	Change
target ≤ 400 ms	420 ms	420 ms	—
	73%	73%	—
	79%	79%	—
	0%	0%	—

R7Cold caches and thundering herds

Anything that makes everyone act at the same instant creates a spike you never sized for.