This figure shows there is only a 0.01% chance of getting more than 360 requests (24 users) per second during peak traffic on a Reddit hug-of-death. Thus, here it will tell show the maximum number of callers they will expect to receive 99% of the time.įigure 3: The cumulative distribution function for the number of server requests per second (from the maximum load of 10 users per second). The CDF gives the probability of receiving a certain number of events or lower per time period. By setting their allowable risk (here, we’ll say full coverage 99% of the time), they can look at the cumulative distribution function (CDF) for the Poisson distribution for their average call rate. The call center would want to model this to determine the minimum staffing required to cover these high-call periods, balancing out their risk of excessive hold times caused by under staffing with the financial cost of adding more customer service agents. Each call comes in independently from each other call, so there might be stretches where no calls arrive or periods where many calls arrive. There is only a 0.01% chance of getting more than 360 requests (24 users) per second during peak traffic on a Reddit hug-of-death.Ī primer on Poisson processes: One of the canonical examples of a Poisson process is the distribution of calls to a call center, where the average rate is known, but the calls come in at random times. Although we don’t have the second-by-second information, we can estimate what it looks like by modeling the user arrivals as a random Poisson process.
The average rate, however, hides the fact that the requests come in randomly and thus this value will fluctuate. To give you an idea of the scale, in 2008 Wikipedia handled 50,000 requests per second with 300 servers. A request is a browser asking for a piece of data on the page (scripts, images, html), and thus one user will make many requests when they arrive.
This works out to an average rate of 157 requests per second and 10 users per second. The peak traffic came at 4:00 PM, during which hour there were 565,310 server requests from 35,870 unique visitors. Figure 1: Hourly totals for server requests, unique visitors, and bandwidth during a trip to Reddit’s front page.
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