Average latency can look healthy while a small fraction of requests take much longer. Tail latency focuses on those slow outcomes because they often determine user-visible delay in distributed systems.
A request that waits for several replicas or services becomes more likely to encounter at least one slow response as fan-out grows. Coordination protocols must therefore account for the tail, not only typical response time.
Acronyms and aliases
long-tail latency variant
Related terms
Frequently asked questions
What does p99 latency mean?
It is the response time below which 99 percent of measured requests complete, leaving one percent slower.
Why does replication increase tail-latency risk?
A coordinated operation can be delayed by its slowest required participant, and more participants create more chances to encounter one.
