On Mon, Dec 8, 2025 at 10:47 PM Thomas Munro <[email protected]> wrote: > Yielding just because you've scanned N index pages/tuples/whatever is > harder to think about. The stream shouldn't get far ahead unless it's > recently been useful for I/O concurrency (though optimal distance > heuristics are an open problem), but in this case a single invocation > of the block number callback can call ReadBuffer() an arbitrary number > of times, filtering out all the index tuples as it rampages through > the whole index IIUC. I see why you might want to yield periodically > if you can, but I also wonder how much that can really help if you > still have to pick up where you left off next time.
I think of it as a necessary precaution against pathological behavior where the amount of memory used to cache matching tuples/TIDs gets out of hand. There's no specific reason to expect that to happen (or no good reason). But I'm pretty sure that it'll prove necessary to pay non-zero attention to how much work has been done since the last time we returned a tuple (when there's a tuple available to return). > I guess it > depends on the distribution of matches. To be clear, I haven't done any kind of modelling of the problems in this area. Once I do that (in 2026), I'll be able to say more about the requirements. Maybe Tomas could take a look sooner? Right now my focus is on getting the basic interfaces/API revisions in better shape. And avoiding regressions while doing so. -- Peter Geoghegan
