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In-Reply-To: <abGv0ScUWVa6eogw@nathan>
From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Wed, 11 Mar 2026 21:49:22 +0300
Message-ID: 
 <CAN55FZ3gdK8dGrEo0M6KFW97OaF8TUbjO_dFoxQKi63davE-jA@mail.gmail.com>
Subject: Re: Speed up COPY FROM text/CSV parsing using SIMD
To: Nathan Bossart <nathandbossart@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>
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Hi,

On Wed, 11 Mar 2026 at 21:09, Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> On Wed, Mar 11, 2026 at 02:36:46PM +0300, Nazir Bilal Yavuz wrote:
> > 0002 has an attempt to remove some branches from SIMD code but since
> > it is kind of functional change, I wanted to attach that as another
> > patch. I think we can apply some parts of this, if not all.
>
> Could you describe what this is doing and what the performance impact is?

SIMD code check these characters:

csv mode: nl, cr, quote and possibly escape.

text mode: nl, cr and bs.

v12 checks them like that:

            if (is_csv)
            {
                match = vector8_or(vector8_eq(chunk, nl),
vector8_eq(chunk, cr));
                match = vector8_or(match, vector8_eq(chunk, quote));
                if (unique_escapec)
                    match = vector8_or(match, vector8_eq(chunk, escape));
            }
            else
            {
                match = vector8_or(vector8_eq(chunk, nl),
vector8_eq(chunk, cr));
                match = vector8_or(match, vector8_eq(chunk, bs));
            }

But actually we know that we will definitely check nl, cr and one of
the quote or bs characters in the code. So, we can introduce a new
variable named bs_or_quote, it will be equal to bs if the mode is text
and it will be equal to quote if the mode is csv. Then, we can remove
the 'if (is_csv)' check and only check for escape ('if
(unique_escapec)'). Now code will look like that:

            match = vector8_or(vector8_eq(chunk, nl), vector8_eq(chunk, cr));
            match = vector8_or(match, vector8_eq(chunk, bs_or_quote));
            if (unique_escapec)
                match = vector8_or(match, vector8_eq(chunk, escape));

That is what v13-0002 does. I saw 1%-2% speedups with this change and
there was no regression.

Regardless of introducing the bs_or_quote variable, we can move 'match
= vector8_or(vector8_eq(chunk, nl), vector8_eq(chunk, cr));' outside
of the if checks, though.

--
Regards,
Nazir Bilal Yavuz
Microsoft