Date: Tue, 17 Mar 2026 13:49:24 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: KAZAR Ayoub <ma_kazar@esi.dz>
Cc: Andres Freund <andres@anarazel.de>,
	Pg Hackers <pgsql-hackers@postgresql.org>,
	Neil Conway <neil.conway@gmail.com>,
	Manni Wood <manni.wood@enterprisedb.com>,
	Andrew Dunstan <andrew@dunslane.net>,
	Shinya Kato <shinya11.kato@gmail.com>,
	Mark Wong <markwkm@gmail.com>,
	Nazir Bilal Yavuz <byavuz81@gmail.com>
Subject: Re: Speed up COPY TO text/CSV parsing using SIMD
Message-ID: <abmiNPQOqBrRlf_m@nathan>
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On Sat, Mar 14, 2026 at 11:43:38PM +0100, KAZAR Ayoub wrote:
> Just a small concern about where some varlenas have a larger binary size
> than its text representation ex:
> SELECT pg_column_size(to_tsvector('SIMD is GOOD'));
>  pg_column_size
> ----------------
>              32
> 
> its text representation is less than sizeof(Vector8) so currently v3 would
> enter SIMD path and exit out just from the beginning (two extra branches)
> because it does this:
> + if (TupleDescAttr(tup_desc, attnum - 1)->attlen == -1 &&
> + VARSIZE_ANY_EXHDR(DatumGetPointer(value)) > sizeof(Vector8))
> 
> I thought maybe we could do * 2 or * 4 its binary size, depends on the type
> really but this is just a proposition if this case is something concerning.

Can we measure the impact of this?  How likely is this case?

> +static pg_attribute_always_inline void CopyAttributeOutText(CopyToState cstate, const char *string,
> +															bool use_simd, size_t len);
> +static pg_attribute_always_inline void CopyAttributeOutCSV(CopyToState cstate, const char *string,
> +														   bool use_quote, bool use_simd, size_t len);

Can you test this on its own, too?  We might be able to separate this and
the change below into a prerequisite patch, assuming they show benefits.

>  			if (is_csv)
> -				CopyAttributeOutCSV(cstate, string,
> -									cstate->opts.force_quote_flags[attnum - 1]);
> +			{
> +				if (use_simd)
> +					CopyAttributeOutCSV(cstate, string,
> +										cstate->opts.force_quote_flags[attnum - 1],
> +										true, len);
> +				else
> +					CopyAttributeOutCSV(cstate, string,
> +										cstate->opts.force_quote_flags[attnum - 1],
> +										false, len);
> +			}
>  			else
> -				CopyAttributeOutText(cstate, string);
> +			{
> +				if (use_simd)
> +					CopyAttributeOutText(cstate, string, true, len);
> +				else
> +					CopyAttributeOutText(cstate, string, false, len);
> +			}

There isn't a terrible amount of branching on use_simd in these functions,
so I'm a little skeptical this makes much difference.  As above, it would
be good to measure it.

-- 
nathan