On Wed, Sep 3, 2025 at 8:16 PM Andres Freund <and...@anarazel.de> wrote: > > I don't see that level of improvement with DIO. For me it's 6054.921 > > ms with prefetching, 8766.287 ms without it. > > I guess your SSD has lower latency than mine...
It's nothing special: a 4 year old Samsung 980 pro. > This actually might be the thing to tackle to avoid this and other similar > regressions: If we were able to isssue combined IOs for interspersed patterns > like we have in this query, we'd easily win back the overhead. And it'd make > DIO much much better. That sounds very plausible to me. I don't think it's at all unusual for index scans to do this (that particular aspect of the test case query wasn't unrealistic). In general this seems important to me. > I don't quite know if this is best done as an optional feature for read > streams, a layer atop read stream or something dedicated. My guess is that it would work best as an optional feature for read streams. A flag like READ_STREAM_REPEAT_READS that's passed to read_stream_begin_relation might work best. > For now I'll go back to working on read stream test infrastructure. That's the > prerequisite for testing the "don't synchronously wait for in-progress IO" > improvement. "don't synchronously wait for in-progress IO" is also very important to this project. Thanks for your help with that. > And if we want to have more complicated merging, that also seems > like something much easier to develop with some testing infra. Great. -- Peter Geoghegan
