Comparison
LatencyvsResponse time
Latency
you measure the delay before the work starts moving, separately from how long the work itself takes.
Strictly, the delay before a transfer or operation begins — network propagation, queueing, scheduling. Casually it is used for total request duration, which is why the word causes so many crossed wires in performance conversations. Say which you mean, because latency and service time have completely different fixes.
Full entry →Response time
you measure what the user actually experiences: request sent to last byte received, queueing and all.
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.
Full entry →