You’ve misunderstood what they’re saying. Not that the benchmark is invalid, but that it’s an incomplete picture if your use case is a mixed set of applications where DB performance is not the only important thing. Hence the comment about memory - O_DIRECT is optimal in terms of DB performance but then the caches are owned by the application and the kernel isn’t free to discard those caches whenever it wants like it can with the page cache. I’m not actually sold on this argument though - I have an embedded DB that with a very tiny block cache goes very very fast, and uses far less RAM than using the page cache because it knows when read ahead is called for vs when it’s not