On Sat, 24 Jun 2023 at 07:43, Ranier Vilela <ranier...@gmail.com> wrote: > I worked a bit more on the v4 version and made a new v6 version, with some > changes.
> I can see some improvement, would you mind testing v6 and reporting back? Please don't bother. I've already mentioned that I'm not going to consider any changes here which are unrelated to changing the rule that Bitmapsets no longer can have trailing zero words. I've already said in [1] that if you have unrelated changes that you wish to pursue in regards to Bitmapset, then please do so on another thread. Also, FWIW, from glancing over it, your v6 patch introduces a bunch of out-of-bounds memory access bugs and a few things are less efficient than I'd made them. The number of bytes you're zeroing using memset in bms_add_member() and bms_add_range() is wrong. bms_del_member() now needlessly rechecks if a->words[wordnum] is 0. We already know it is 0 from the above check. You may have misunderstood the point of swapping for loops for do/while loops? They're meant to save the needless loop bounds check on the initial loop due to the knowledge that the Bitmapset contains at least 1 word. Additionally, it looks like you've made various places that loop over the set and check for the "lastnonzero" less efficiently by adding an additional surplus check. Depending on the CPU architecture, looping backwards over arrays can be less efficient due to lack of hardware prefetching when accessing memory in reverse order. It's not clear to me why you think looping backwards is faster. I've no desire to introduce code that needlessly performs more slowly depending on the ability of the hardware prefetcher on the CPU architecture PostgreSQL is running on. Also, if you going to post benchmark results, they're not very meaningful unless you can demonstrate what you actually tested. You've mentioned nothing here to say what query-b.sql contains. David [1] https://postgr.es/m/caaphdvo65dxfzcgjz7pvxs75vut+1-wsap_kvefwgsns2y2...@mail.gmail.com
