Notes

Queueing theory originated in 1909 with a paper written by a mathematician named Agner Krarup Erlang.
 He accurately estimated the probability that a call would be blocked at different capacity utilization levels.

It can provide essential insights to product developers because there're similar problems of unpredictable work arrival times and task durations.

Queueing systems:
 Queue: the waiting work.
 Server: the resource performing the work, whose time to complete the work may be unpredictable.
 Arrival Process: the pattern with which work arrives. It's usually unpredictable.
 Service Process: the process in which the server accomplishes the work.
 Queueing discipline: how queue handles the waiting work, the rules under which an organization processes incoming items. For example, First Come, First Served, Last In First Out, First In Still Here, etc.

Kendall notation: $M/M/1/\infty$ queue.
 The first $M$ refers to the arrival process, in this case, is the Markov process.
 The second $M$ refers to the service process, which is also a Markov process.
 The number $1$ refers to the number of parallel servers in the system.
 The final term $\infty$ describes the upper limit on queue size.