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From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Thu, 14 Aug 2025 13:29:35 +0300
Message-ID: 
 <CAN55FZ0houfWHn8_MEEefhprZvc33jr07GrBYo+Bp2yw=TVnKA@mail.gmail.com>
Subject: Re: Speed up COPY FROM text/CSV parsing using SIMD
To: KAZAR Ayoub <ma_kazar@esi.dz>
Cc: Shinya Kato <shinya11.kato@gmail.com>, pgsql-hackers@postgresql.org
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Hi,

On Thu, 14 Aug 2025 at 05:25, KAZAR Ayoub <ma_kazar@esi.dz> wrote:
>
> Following Nazir's findings about 4096 bytes being the performant line length, I did more benchmarks from my side on both TEXT and CSV formats with two different cases of normal data (no special characters) and data with many special characters.
>
> Results are con good as expected and similar to previous benchmarks
>  ~30.9% faster copy in TEXT format
>  ~32.4% faster copy in CSV format
> 20%-30% reduces cycles per instructions
>
> In the case of doing a lot of special characters in the lines (e.g., tables with large numbers of columns maybe), we obviously expect regressions here because of the overhead of many fallbacks to scalar processing.
> Results for a 1/3 of line length of special characters:
> ~43.9% slower copy in TEXT format
> ~16.7% slower copy in CSV format
> So for even less occurrences of special characters or wider distance between there might still be some regressions in this case, a non-significant case maybe, but can be treated in other patches if we consider to not use SIMD path sometimes.
>
> I hope this helps more and confirms the patch.

Thanks for running that benchmark! Would you mind sharing a reproducer
for the regression you observed?

--
Regards,
Nazir Bilal Yavuz
Microsoft