Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs
От | Nathan Bossart |
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Тема | Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs |
Дата | |
Msg-id | 20240322144739.GA2321246@nathanxps13 обсуждение исходный текст |
Ответ на | Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs
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Список | pgsql-hackers |
On Thu, Mar 21, 2024 at 08:59:54PM -0400, Tom Lane wrote: > Nathan Bossart <nathandbossart@gmail.com> writes: >> On Thu, Mar 21, 2024 at 03:40:12PM -0500, Nathan Bossart wrote: >>> On Thu, Mar 21, 2024 at 04:31:45PM -0400, Tom Lane wrote: >>>> I don't think we have any really cheap way to de-duplicate the role >>>> OIDs, especially seeing that it has to be done on-the-fly within the >>>> collection loop, and the order of roles_list is at least potentially >>>> interesting. Not sure how to make further progress without a lot of >>>> work. > >>> Assuming these are larger lists, this might benefit from optimizations >>> involving SIMD intrinsics. > >> Never mind. With the reproduction script, I'm only seeing a ~2% >> improvement with my patches. > > Yeah, you cannot beat an O(N^2) problem by throwing SIMD at it. I apparently had some sort of major brain fade when I did this because I didn't apply your hashing patch when I ran this SIMD test. With it applied, I see a speedup of ~39%, which makes a whole lot more sense to me. If I add the Bloom patch (updated with your suggestions), I get another ~73% improvement from there, and a much smaller regression in the role creation portion. hash hash+simd hash+simd+bloom create 1.27 1.27 1.28 grant 0.18 0.11 0.03 -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
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