Backend & systems·Scaling and load management
you measure what the user actually experiences: request sent to last byte received, queueing and all.
Response time
Also calledend-to-end latency, wall clock time
The total elapsed time a client observes, comprising network latency, queueing delay and service time. It is the number that matters to users and the one to put in an SLO. Under load it is dominated by queueing rather than processing, which is why optimising the handler does nothing once the system is saturated.