Em qua., 14 de jul. de 2021 às 21:21, David Rowley <dgrowle...@gmail.com> escreveu:
> On Thu, 15 Jul 2021 at 12:10, Ranier Vilela <ranier...@gmail.com> wrote: > > > > Em qua., 14 de jul. de 2021 às 20:43, David Rowley <dgrowle...@gmail.com> > escreveu: > >> > >> On Thu, 15 Jul 2021 at 05:55, Ranier Vilela <ranier...@gmail.com> > wrote: > >> > I repeated (3 times) the benchmark with v8 here, > >> > and the results were not good. > >> > >> Do you have any good theories on why the additional branching that's > >> done in v7b vs v8 might cause it to run faster? > > > > > > Branch Predictions works with *more* probable path, > > otherwise a penalty occurs and the cpu must revert the results. > > But, in v8 there is no additional branch, so no branch to mispredict. > I don't really see how your explanation fits. > In v8 the branch occurs at : + if (ExecGetResultType(outerPlanState(sortstate))->natts == 1) datumSort is tested first. Cpu time is a more expensive resource. Always is executed two branches, if it is right path, win, otherwise occurs a penalty time. > It seems much more likely to me that the results were just noisy. It > would be good to see if you can recreate them consistently. > I do. Can you please share results with v7b? regards, Ranier Vilela
