Em seg., 4 de mar. de 2024 às 03:18, Andrey M. Borodin <x4...@yandex-team.ru> escreveu:
> > > > On 14 Jan 2024, at 18:55, John Naylor <johncnaylo...@gmail.com> wrote: > > > > On Sat, Jan 13, 2024 at 9:36 PM Ranier Vilela <ranier...@gmail.com> > wrote: > >> > >> Em ter., 9 de jan. de 2024 às 06:31, John Naylor < > johncnaylo...@gmail.com> escreveu: > > > >>> This just moves an operation from one place to the other, while > >>> obliterating the explanatory comment, so I don't see an advantage. > >> > >> Well, I think that is precisely the case for using memset. > >> The way initialization is currently done is much slower and harmful to > the branch. > >> Of course, the gain should be small, but it is fully justified for > switching to memset. > > > > We haven't seen any evidence or reasoning for that. Simple > > rules-of-thumb are not enough. > > > > Hi Ranier, > > I’ll mark CF entry [0] as “Returned with Feedback”. Feel free to reopen > item in this CF or submit to the next, if you want to continue working on > this. > > I took a glance into the patch, and I would agree that setting field > nonzero values with memset() is somewhat unusual. Please provide stronger > evidence to do so. > I counted the calls with non-zero memset in the entire postgres code and they are about 183 calls. I counted the calls with non-zero memset in the entire postgres code and they are about 183 calls. At least 4 calls with -1 File contrib\pg_trgm\trgm_op.c: memset(lastpos, -1, sizeof(int) * len); File src\backend\executor\execPartition.c: memset(pd->indexes, -1, sizeof(int) * partdesc->nparts); File src\backend\partitioning\partprune.c: memset(subplan_map, -1, nparts * sizeof(int)); memset(subpart_map, -1, nparts * sizeof(int)); Does filling a memory area, one by one, with branches, need strong evidence to prove that it is better than filling a memory area, all at once, without branches? best regards, Ranier Vilela
