On Infinite Scalability - Ayende @ Rahien →
Why do we need that buffer?
There are several reasons to want to do that. First, we assume that the system is going to be in production for a relatively long time, so the # of user or their activity is going to grow. Second, in most systems, we are usually talking about some % of the users being active, but there are usually times when you have a significantly more users being active. For example, at end of tax year, an accounting system can be expected to see a greater utilization, as well as at every end of the month.
And within that buffer, we don’t need to change the system architecture, we just need to add more resources to the system.
And why a full order of magnitude?
Put simply, because it is relatively easy to get there. Let us assume end of year again, and now we have 15,000 active users (vs. the “normal” 5,000). But the amount of work we do isn’t directly related to the number of users. It is related to how active they are and what operations they are doing. In such a scenario, it is more likely that the users will be more active and stress the system more.
