Horton

Re: Speed up COPY FROM text/CSV parsing using SIMD

KAZAR Ayoub <ma_kazar@esi.dz>

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From: KAZAR Ayoub <ma_kazar@esi.dz>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Nazir Bilal Yavuz <byavuz81@gmail.com>, Andrew Dunstan <andrew@dunslane.net>, Shinya Kato <shinya11.kato@gmail.com>, Manni Wood <manni.wood@enterprisedb.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2025-11-26T11:50:58Z
Lists: pgsql-hackers

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Hello,
On Wed, Nov 19, 2025 at 10:01 PM Nathan Bossart <nathandbossart@gmail.com>
wrote:

> On Tue, Nov 18, 2025 at 05:20:05PM +0300, Nazir Bilal Yavuz wrote:
> > Thanks, done.
>
> I took a look at the v3 patches.  Here are my high-level thoughts:
>
> +    /*
> +     * Parse data and transfer into line_buf. To get benefit from
> inlining,
> +     * call CopyReadLineText() with the constant boolean variables.
> +     */
> +    if (cstate->simd_continue)
> +        result = CopyReadLineText(cstate, is_csv, true);
> +    else
> +        result = CopyReadLineText(cstate, is_csv, false);
>
> I'm curious whether this actually generates different code, and if it does,
> if it's actually faster.  We're already branching on cstate->simd_continue
> here.

I've compiled both versions with -O2 and confirmed they generate different
code. When simd_continue is passed as a constant to CopyReadLineText, the
compiler optimizes out the condition checks from the SIMD path.
A small benchmark on a 1GB+ file shows the expected benefit which is around
6% performance improvement.
I've attached the assembly outputs in case someone wants to check something
else.


Regards,
Ayoub Kazar