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

Hi,

On Thu, 12 Mar 2026 at 20:37, Nathan Bossart <nathandbossart(at)gmail(dot)com> wrote:
>
> Here is what I have staged for commit, which I'm planning to do tomorrow.
> Please review and/or test if you are able.

Thank you!

Unfortunately, v15 causes a regression for a 'csv & wide & 1/3' case
on my end. v14 was taking 8000ms but v15 took ~9100ms. If we add the
tmp_hit_eof variable then the regression disappears. Also, if I use a
struct like below, regression disappears again.

typedef struct CopyReadLineSIMDResult
{
int input_buf_ptr;
bool hit_eof;
bool result;
} CopyReadLineSIMDResult;

When I removed the tmp_hit_eof variable on v14, I didn't encounter any
regression. I really don't understand why this is happening on my end.
Manni didn't encounter any regression on the benchmark [1].

I benchmarked v15 and both of the cases above:

------------------------------------------------------------

Results for default_toast_compression = 'lz4':

+--------------------------------------------------+
| Optimization: -O2 |
+-------------------+--------------+---------------+
| | Text | CSV |
+-------------------+------+-------+-------+-------+
| WIDE | None | 1/3 | None | 1/3 |
+-------------------+------+-------+-------+-------+
| Old master | 4260 | 4789 | 5930 | 8276 |
+-------------------+------+-------+-------+-------+
| v14 | 2489 | 4439 | 2529 | 8098 |
+-------------------+------+-------+-------+-------+
| v15 | 2494 | 4235 | 2490 | 9140 |
+-------------------+------+-------+-------+-------+
| v15 + tmp_hit_eof | 2487 | 4539 | 2478 | 8041 |
+-------------------+------+-------+-------+-------+
| v15 + struct | 2490 | 4531 | 2483 | 7756 |
+-------------------+------+-------+-------+-------+
| | | | | |
+-------------------+------+-------+-------+-------+
| | | | | |
+-------------------+------+-------+-------+-------+
| | Text | CSV |
+-------------------+------+-------+-------+-------+
| NARROW | None | 1/3 | None | 1/3 |
+-------------------+------+-------+-------+-------+
| Old master | 9955 | 10056 | 10329 | 10872 |
+-------------------+------+-------+-------+-------+
| v14 | 9917 | 10080 | 10104 | 10510 |
+-------------------+------+-------+-------+-------+
| v15 | 9898 | 10062 | 10232 | 10483 |
+-------------------+------+-------+-------+-------+
| v15 + tmp_hit_eof | 9847 | 10004 | 10192 | 10437 |
+-------------------+------+-------+-------+-------+
| v15 + struct | 9877 | 10008 | 10107 | 10521 |
+-------------------+------+-------+-------+-------+

------------------------------------------------------------

Results for default_toast_compression = 'pglz':

+---------------------------------------------------+
| Optimization: -O2 |
+-------------------+---------------+---------------+
| | Text | CSV |
+-------------------+-------+-------+-------+-------+
| WIDE | None | 1/3 | None | 1/3 |
+-------------------+-------+-------+-------+-------+
| Old master | 10579 | 10927 | 12276 | 14488 |
+-------------------+-------+-------+-------+-------+
| v14 | 8832 | 10646 | 8815 | 14352 |
+-------------------+-------+-------+-------+-------+
| v15 | 8859 | 10489 | 8835 | 15414 |
+-------------------+-------+-------+-------+-------+
| v15 + tmp_hit_eof | 8828 | 10829 | 8840 | 14297 |
+-------------------+-------+-------+-------+-------+
| v15 + struct | 8847 | 10829 | 8846 | 14003 |
+-------------------+-------+-------+-------+-------+
| | | | | |
+-------------------+-------+-------+-------+-------+
| | | | | |
+-------------------+-------+-------+-------+-------+
| | Text | CSV |
+-------------------+-------+-------+-------+-------+
| NARROW | None | 1/3 | None | 1/3 |
+-------------------+-------+-------+-------+-------+
| Old master | 9952 | 10342 | 10112 | 10861 |
+-------------------+-------+-------+-------+-------+
| v14 | 9907 | 10344 | 10103 | 10492 |
+-------------------+-------+-------+-------+-------+
| v15 | 9897 | 10261 | 10126 | 10490 |
+-------------------+-------+-------+-------+-------+
| v15 + tmp_hit_eof | 9848 | 10218 | 10184 | 10425 |
+-------------------+-------+-------+-------+-------+
| v15 + struct | 9858 | 10150 | 10116 | 10464 |
+-------------------+-------+-------+-------+-------+

------------------------------------------------------------

It can be seen that the 'csv & wide & 1/3' case is much better on 'v15
+ struct' and 'v15 + tmp_hit_eof' but 'text & wide & 1/3' case is a
bit worse but still better than master.

Regardless of the issues above, I encountered a compiler warning on
the v15, if 'USE_NO_SIMD' is defined, then this warning appears:

copyfromparse.c:1780:1: warning: label ‘out’ defined but not used
[-Wunused-label]

Rest of the changes look good to me. v16 is attached, it fixes the
warning by protecting 'out' with '#ifndef USE_NO_SIMD', no other
changes. In addition to that, I put 'using CopyReadLineSIMDResult
struct' as a 0002 to get an opinion.

[1] https://postgr.es/m/CAKWEB6pMbdMDvhfaX1Z0eSULVQFYhEhssaRHdOxAX_5OYubxKw%40mail.gmail.com

--
Regards,
Nazir Bilal Yavuz
Microsoft