Re: index prefetching

On Wed, Aug 6, 2025 at 9:35 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> On Tue, Aug 5, 2025 at 4:56 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
> > True, the complex patch could prefetch the leaf pages.

There must be a similar opportunity for parallel index scans. It has
that "seize the scan" concept where parallel workers do one-at-a-time
locked linked list leapfrog.

> What I meant was that the complex patch can make up for the fact that
> direct I/O presumably won't ever have an equivalent to simple
> read-ahead. Just by having a very flexible prefetching implementation
> (and without any special sequential access heuristics ever being
> required).

I'm not so sure, there are certainly opportunities in different layers
of the system. I'm going to dust off a couple of experimental patches
(stuff I talked to Peter about back in Athens), and try to describe
some other vague ideas Andres and I have bounced around over the past
few years when chatting about what you lose when you turn on direct
I/O. Basically, the stuff that we can't fix with "precise" I/O
streaming as I like to call it, where it might still be interesting to
think about opportunities to do fuzzier speculative lookahead. I'll
start a new thread.