R8Hedged requests: beating tail latency

The problem

1 s on screen = 100 ms

Every server is fast. Why is the page still slow so often?

Wait for the slowest of five

A page asks five shards at once and waits for all five. Each takes 20 ms, but one in 20 is twelve times slower.

Live metrics for each version of the scene
Metric	The tail	Hedged	Change
target ≤ 400 ms	—	—	—
target ≤ 400 ms	—	—	—
	—	—	—

R8Hedged requests: beating tail latency

When a page fans out to many servers, one straggler makes it slow. Send a backup request once the 95th percentile has passed.