po 24. 8. 2020 v 21:43 odesÃlatel Pavel Stehule <pavel.steh...@gmail.com> napsal:
> > > 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 > I think it can work. It is a good enough solution for people who need a different behaviour with minimal impact on people who don't need a change. Regards Pavel > > Regards > > Pavel > >> >> regards, tom lane >> >>
