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From: KAZAR Ayoub <[email protected]>
To: Nathan Bossart <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Shinya Kato <[email protected]>
Cc: Manni Wood <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Speed up COPY FROM text/CSV parsing using SIMD
Date: Wed, 26 Nov 2025 12:50:58 +0100
Message-ID: <CA+K2Rump8NoMRZRZ2r4jHXUJwByasy_c3_b0oaO+TLkSbMD-jw@mail.gmail.com> (raw)
In-Reply-To: <aR4wDwNdLc5TmcQq@nathan>
References: <aPkvi5P7kpA8oQKc@nathan>
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Hello,
On Wed, Nov 19, 2025 at 10:01 PM Nathan Bossart <[email protected]>
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


Attachments:

  [application/octet-stream] copyfromparse-constant.asm (48.0K, 3-copyfromparse-constant.asm)
  download

  [application/octet-stream] copyfromparse-variable.asm (47.1K, 4-copyfromparse-variable.asm)
  download

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