On Mon, Feb 10, 2025 at 1:11 PM Tomas Vondra <to...@vondra.me> wrote: > Certainly for the "localized" regressions, and cases when bitmapheapscan > would not be picked. The eic=1 case makes me a bit more nervous, because > it's default and affects NVMe storage. Would be good to know why is > that, or perhaps consider bumping up eic default. Not sure.
I'm relatively upset by the fact that effective_io_concurrency is measured in units that are, AFAIUI, completely stupid. The original idea was that you would set it to the number of spindles you have. But from what I have heard, that didn't actually work: you needed to set it to a significantly higher number. But in 2025, you probably don't even have spindles any more, because you're probably on SSD or some other modern storage medium rather than a rotating hard drive. And if you do have spindles, do you know how many you have? Is that even a meaningful concept? I am not saying that it's this patch's job to replace effective_io_concurrency with something better. I think adopting the streaming read interface is pretty important, and if it works out that we should also change the default effective_io_concurrency from 1 to 2 or 17 or 42715 in the same release, fine. But I think that in the slightly longer term, it would be a really good idea for someone to propose a more sensible model. It's hard to think of a clearer case of a parameter being rendered meaningless by the march of technology. The closest analogue that comes to mind is our sorting implementation used to have a hard coded number of tape drives, when the underlying implementation was a bunch of files all on the same filesystem, but that wasn't a user-settable parameter. -- Robert Haas EDB: http://www.enterprisedb.com
