Sometimes my customers (especially the ones who are used to different database servers,) ask me about the CPU and memory consumption of a MySQL server process.
Initially I thought that this kind of requests were rather odd, mostly because the whole box was dedicated to the database, thus measuring the global usage of CPU and memory could give a rough estimate of how well the database server is performing.
With time, I came to appreciate the request, and I started digging into the operating system intricacies to find out as much as I could about the resources used by a single process. This information can be useful if there are different services running in the same machine, and it could be of paramount importance to find out if your DBMS process can exceed the operating system resources.
My measurements are referred to the GNU/Linux operating system. Other systems have different ways of gathering the same data.