If he’s processing LLMs or really any non-trivial DB (read: any business DB)

Actually... as a former DBA on large databases, you typically want to minimize swapping on a dedicated database system. Most database engines do a much better job at keeping useful data in memory than the Linux kernel's file caching, which is agnostic about what your files contain. There are some exceptions, like elasticsearch which almost entirely relies on the Linux filesystem cache for buffering I/O.

Anyway, database engines have query optimizers to determine the optimal path to resolve a query, but they rely on it that the buffers that they consider to be "in memory" are actually residing in physical memory, and not sitting in a swapfile somewhere.

So typically, on a large database system the vendor recommendation will be to set vm.swappiness=0 to minimize memory pressure from filesystem caching, and to set the database buffers as high as the amount of memory you have in your system minus a small amount for the operating system.