Re: Speed up COPY FROM text/CSV parsing using SIMD - Mailing list pgsql-hackers

Hi,

On Thu, 12 Mar 2026 at 20:37, Nathan Bossart <nathandbossart@gmail.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