Tomas Vondra digs into some metrics:
I do a fair number of benchmarks, not only to validate patches, but also to find interesting (suspicious) stuff to improve. It’s an important part of my development workflow. And it’s fun 😉 But we’re dealing with complex systems (hardware, OS, DB, application), and that brings challenges. Every now and then I run into something that I don’t quite understand.
Consider a read-only pgbench, the simplest workload there is, with a single
SELECTdoing lookup by PK. If you do this with a small data set on any machine, the expectation is near linear scaling up to the number of cores. It’s not perfect, CPUs have frequency scaling and power management, but it should be close.
Click through for a quick look at some odd behavior, followed by a lot of interesting digging into the weeds trying to find answers.