On 2018-06-18 16:44:09 -0400, Robert Haas wrote: > On Sat, Jun 16, 2018 at 3:41 PM, Andres Freund <and...@anarazel.de> wrote: > >> The posix_fadvise approach is not perfect, no doubt about that. But it > >> works pretty well for bitmap heap scans, and it's about 13249x better > >> (rough estimate) than the current solution (no prefetching). > > > > Sure, but investing in an architecture we know might not live long also > > has it's cost. Especially if it's not that complicated to do better. > > My guesses are: > > - Using OS prefetching is a very small patch. > - Prefetching into shared buffers is a much bigger patch.
Why? The majority of the work is standing up a bgworker that does prefetching (i.e. reads WAL, figures out reads not in s_b, does prefetch). Allowing a configurable number + some synchronization between them isn't that much more work. > - It'll be five years before we have direct I/O. I think we'll have lost a significant market share by then if that's the case. Deservedly so. Greetings, Andres Freund
