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help / color / mirror / Atom feedFrom: Manni Wood <[email protected]>
To: Nathan Bossart <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Cc: KAZAR Ayoub <[email protected]>
Cc: Neil Conway <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Cc: Shinya Kato <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Speed up COPY FROM text/CSV parsing using SIMD
Date: Mon, 9 Mar 2026 21:30:21 -0500
Message-ID: <CAKWEB6oE_1aNRV-utrAkUbYhM-0z1fZRvYLrDC4SxfW-UXOmpA@mail.gmail.com> (raw)
In-Reply-To: <aa8QlTVEDhG1JU0Z@nathan>
References: <CAKWEB6pq7C0Wv1wT9Y1_c_1fn-+cR8pb210Pj3w2FcEOmNGxbQ@mail.gmail.com>
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<aa8QlTVEDhG1JU0Z@nathan>
On Mon, Mar 9, 2026 at 1:25 PM Nathan Bossart <[email protected]>
wrote:
> On Wed, Mar 04, 2026 at 06:15:53PM +0300, Nazir Bilal Yavuz wrote:
> > +#ifndef USE_NO_SIMD
> > +static bool CopyReadLineTextSIMDHelper(CopyFromState cstate, bool
> is_csv,
> > +
> bool *temp_hit_eof, int *temp_input_buf_ptr);
> > +#endif
>
> Should we inline this, too?
>
> > + /*
> > + * Do not disable SIMD when we hit EOL or
> EOF characters. In
> > + * practice, it does not matter for EOF
> because parsing ends
> > + * there, but we keep the behavior
> consistent.
> > + */
> > + if (!(simd_hit_eof || simd_hit_eol))
> > + cstate->simd_enabled = false;
>
> nitpick: I would personally avoid disabling it for EOF. It probably
> doesn't amount to much, but I don't see any point in the extra
> complexity/work solely for consistency.
>
> > + /*
> > + * We encountered a EOL or EOF on the
> first vector. This means
> > + * lines are not long enough to skip fully
> sized vector. If
> > + * this happens two times consecutively,
> then disable the
> > + * SIMD.
> > + */
> > + if (first_vector)
> > + {
> > + if
> (cstate->simd_failed_first_vector)
> > + cstate->simd_enabled =
> false;
> > +
> > + cstate->simd_failed_first_vector =
> true;
> > + }
>
> The first time I saw this, my mind immediately went to the extreme case
> where this likely regresses: alternating long and short lines. We might
> just want to disable it the first time we see a short line, like we do for
> special characters. This is another thing that we can improve
> independently later on.
>
> > + /* First try to run SIMD, then continue with the scalar path */
> > + if (cstate->simd_enabled)
> > + {
> > + int temp_input_buf_ptr = input_buf_ptr;
> > + bool temp_hit_eof = false;
> > +
> > + result = CopyReadLineTextSIMDHelper(cstate, is_csv,
> &temp_hit_eof,
> > +
> &temp_input_buf_ptr);
> > + input_buf_ptr = temp_input_buf_ptr;
> > + hit_eof = temp_hit_eof;
>
> Given CopyReadLineTextSIMDHelper() doesn't have too much duplicated code,
> moving the SIMD stuff to its own function is nice. The temp variables seem
> a bit too magical to me, though. If those really make a difference, IMHO
> there ought to be a big comment explaining why.
>
> --
> nathan
>
Here are some benchmarks showing what performance will look like for users
who continue to use default_toast_compression = pglz.
all compiled by meson with debugoptimized (-g -O2)
arm NARROW master without inline (git revert
dc592a41557b072178f1798700bf9c69cd8e4235) default_toast_compression = pglz
TXT : 10055.141000 ms
CSV : 10549.174500 ms
TXT with 1/3 escapes: 10213.864750 ms
CSV with 1/3 quotes: 12188.039000 ms
arm NARROW master with inline with v11patch default_toast_compression = pglz
TXT : 10070.153750 ms -0.149304% regression
CSV : 10161.348750 ms 3.676361% improvement
TXT with 1/3 escapes: 10618.005000 ms -3.956781% regression
CSV with 1/3 quotes: 12279.366250 ms -0.749319% regression
arm WIDE master without inline (git revert
dc592a41557b072178f1798700bf9c69cd8e4235) default_toast_compression = pglz
TXT : 11355.602750 ms
CSV : 13893.110500 ms
TXT with 1/3 escapes: 12872.690500 ms
CSV with 1/3 quotes: 16722.262500 ms
arm WIDE master with inline with v11patch default_toast_compression = pglz
TXT : 9001.007250 ms 20.735099% improvement
CSV : 8988.679750 ms 35.301171% improvement
TXT with 1/3 escapes: 12191.137000 ms 5.294569% improvement
CSV with 1/3 quotes: 16297.541500 ms 2.539854% improvement
x86 NARROW master without inline (git revert
dc592a41557b072178f1798700bf9c69cd8e4235) default_toast_compression = pglz
TXT : 26243.084500 ms
CSV : 27719.564000 ms
TXT with 1/3 escapes: 29578.192750 ms
CSV with 1/3 quotes: 34467.571250 ms
x86 NARROW master with inline with v11patch default_toast_compression = pglz
TXT : 26371.996750 ms -0.491224% regression
CSV : 26137.186500 ms 5.708522% improvement
TXT with 1/3 escapes: 28080.201000 ms 5.064514% improvement
CSV with 1/3 quotes: 32557.377500 ms 5.542003% improvement
x86 WIDE master without inline (git revert
dc592a41557b072178f1798700bf9c69cd8e4235) default_toast_compression = pglz
TXT : 28734.774750 ms
CSV : 35700.485000 ms
TXT with 1/3 escapes: 32376.878250 ms
CSV with 1/3 quotes: 47024.985750 ms
x86 WIDE master with inline with v11patch default_toast_compression = pglz
TXT : 22753.755750 ms 20.814567% improvement
CSV : 22977.195500 ms 35.638982% improvement
TXT with 1/3 escapes: 29526.887000 ms 8.802551% improvement
CSV with 1/3 quotes: 40298.196750 ms 14.304712% improvement
--
-- Manni Wood EDB: https://www.enterprisedb.com
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