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

On Wed, Nov 26, 2025 at 5:51 AM KAZAR Ayoub <ma_kazar@esi.dz> wrote:

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

Correction to my last post:

I also tried files that alternated lines with no special characters and lines with 1/3rd special characters, thinking I could force the algorithm to continually check whether or not it should use simd and therefore force more overhead in the try-simd/don't-try-simd housekeeping code. The text file was still 20% faster (not 50% faster as I originally stated --- that was a typo). The CSV file was still 13% faster.

Also, apologies for posting at the top in my last e-mail.

--

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