Date: Fri, 13 Mar 2026 09:05:13 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: Nazir Bilal Yavuz <byavuz81@gmail.com>
Cc: Manni Wood <manni.wood@enterprisedb.com>, KAZAR Ayoub <ma_kazar@esi.dz>,
	Neil Conway <neil.conway@gmail.com>,
	Andrew Dunstan <andrew@dunslane.net>,
	Shinya Kato <shinya11.kato@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Speed up COPY FROM text/CSV parsing using SIMD
Message-ID: <abQZmZ0KZesCxfR0@nathan>
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On Fri, Mar 13, 2026 at 04:34:49PM +0300, Nazir Bilal Yavuz wrote:
> On Fri, 13 Mar 2026 at 14:57, Nazir Bilal Yavuz <byavuz81@gmail.com> wrote:
>> Unfortunately, v15 causes a regression for a 'csv & wide & 1/3' case
>> on my end. v14 was taking 8000ms but v15 took ~9100ms. If we add the
>> tmp_hit_eof variable then the regression disappears. Also, if I use a
>> struct like below, regression disappears again.
> 
>> When I removed the tmp_hit_eof variable on v14, I didn't encounter any
>> regression. I really don't understand why this is happening on my end.
>> Manni didn't encounter any regression on the benchmark [1].
> 
> Problem might be related to gcc. I am using Debian Trixie and my
> current gcc version is 'gcc version 14.2.0 (Debian 14.2.0-19)'. If I
> compile Postgres with 'Debian clang version 19.1.7 (3+b1)', then there
> is no regression, which makes more sense IMO.

Let's just re-add the temporary variable for hit_eof.  The struct idea is
clever, but it's just a little more complicated than I think is necessary
here.

I've also removed the goto in favor of just duplicating the "out" code,
like you had before.  I'd like to avoid sporadic #ifndef USE_NO_SIMD uses,
and goto is out of fashion, anyway.

-- 
nathan

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