> The best you will ever do, even with full application knowledge and complete control of the machine, is an LRU cache replacement algorithm

First of all, even the kernel can do better than simple LRU. We have MGLRU now for example. That said, the kernel is at a structural disadvantage.

A general purpose eviction and prefetch algorithm is like an automatic transmission on a car. It can react only to what it's seen.

When you drive stick, you can react to what you can see on the road ahead of you. A database has a query plan. It can see the future as well as remember the past. It has more information than the kernel.

> So a simpleminded LRU always makes optimal use of available cache, regardless of access pattern or other load on the system

That cannot be true. If I have a random access pattern, LRU will perform no better than random. If I have a future-oracle, I can just evict what's most distant in my set of future accesses.

Regardless of whether you're right about the suitability of LRU for this or that workload, it's simply false, mathematically, from a computer science POV, that LRU is optimal.

And if you go around making confidently wrong claims like this, one must wonder about what else you are wrong. If you want to be disagreeable in public, fine: just make sure you have math on your side first.