Performance Analysis
What happens to request waiting time as server utilization (fraction of busy time) approaches 100%?
- AIt grows sharply (the increase accelerates as utilization rises)
- BIt grows gradually in proportion to utilization
- CHigher utilization shortens waiting time
Show answer and explanation
Answer: A. It grows sharply (the increase accelerates as utilization rises)
When requests arrive irregularly, queues form whenever arrivals happen to bunch up, even if the server has idle time. The higher the utilization, the less idle time there is to drain queues, so waiting time grows sharply, roughly in proportion to 1 ÷ (1 − ρ) for utilization ρ. Waiting times at 50% and 90% utilization differ several-fold. Systems where responsiveness matters therefore keep utilization headroom.
- A. Correct. That is why systems are run with headroom.
- B. It is not proportional; it grows sharply.
- C. It grows longer instead.