Re: SIMD optimization for list_sort

From: John Naylor <johncnaylorls(at)gmail(dot)com>
To: "R, Rakshit" <rakshit(dot)r(at)intel(dot)com>
Cc: "Devulapalli, Raghuveer" <raghuveer(dot)devulapalli(at)intel(dot)com>, Andrei Lepikhov <lepihov(at)gmail(dot)com>, "Giacchino, Luca" <luca(dot)giacchino(at)intel(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "Shankaran, Akash" <akash(dot)shankaran(at)intel(dot)com>, "Paul, Sourav Kumar" <sourav(dot)kumar(dot)paul(at)intel(dot)com>
Subject: Re: SIMD optimization for list_sort
Date: 2025-02-28 12:36:08
Message-ID: CANWCAZZd7PLGoi=a7-KLbMmtr+oaWe0dhiyJLUfamyi3KZbT8A@mail.gmail.com
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On Fri, Feb 28, 2025 at 12:43 PM R, Rakshit <rakshit(dot)r(at)intel(dot)com> wrote:

> > I don't think "another extension might use it someday" makes a very strong case,
> > particularly for something that requires a new dependency.
>
> The x86-simdsort library is an optional dependency in Postgres. Also the new list sort implementation which uses the x86-simdsort library does not impact any of the existing workflows in Postgres.

"Optional" and "Does not impact" are not great selling points to get
us to take a 1500 line patch. As we told you in November, list_sort
isn't critical for us. You need to start with the user and work
backwards to the technology. Don't pick a technology and try to sell
people on using it.

> We ran our extension to stress list sort with low cardinality inputs. For eg, for an array of size 100k having repeated values in the range 1-10 we still see a gain of around 20% in throughput.
> We will collect more data for low cardinality inputs and with AVX2 too.

Thanks for the news, those are encouraging results.

--
John Naylor
Amazon Web Services

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