It's important to note that for interactive applications, queues can have surprisingly little capacity and still provide all the demand levelling necessary. Tec

It's important to note that for interactive applications, queues can have surprisingly little capacity and still provide all the demand levelling necessary. Technically this depends on the variance of the arrivals, but in my practical experience, even quite bursty arrivals are often well-behaved enough that a second or so of queue capacity is sufficient. Any time I've had queues need more than a second of capacity has been when the system is broken and user experience has already degraded to the point where it might be better for the median user to shed a small amount of load to get back to a sub-second queue. (In batch processing where you aim for maximum throughput, obviously you need a long queue to make sure you never run out of job.)