ne 23. 8. 2020 v 23:08 odesÃlatel Tom Lane <t...@sss.pgh.pa.us> napsal:
> Pavel Stehule <pavel.steh...@gmail.com> writes: > > I am sending a patch that is years used in GoodData. > > I'm quite unexcited about that. I'd be the first to agree that the > ten-pages estimate is a hack, but it's not an improvement to ask users > to think of a better value ... especially not as a one-size-fits- > all-relations GUC setting. > This patch is just a workaround that works well 10 years (but for one special use case) - nothing more. Without this patch that application cannot work ever. > I did have an idea that I think is better than my previous one: > rather than lying about the value of relpages, let's represent the > case where we don't know the tuple density by setting reltuples = -1 > initially. This leads to a patch that's a good bit more invasive than > the quick-hack solution, but I think it's a lot cleaner on the whole. > > A possible objection is that this changes the FDW API slightly, as > GetForeignRelSize callbacks now need to deal with rel->tuples possibly > being -1. We could avoid an API break if we made plancat.c clamp > that value to zero; but then FDWs still couldn't tell the difference > between the "empty" and "never analyzed" cases, and I think this is > just as much of an issue for them as for the core code. > > I'll add this to the upcoming CF. > I'll check it Regards Pavel > > regards, tom lane > >
