Re: Performance improvements for src/port/snprintf.c

On 2018-08-17 14:32:59 -0400, Tom Lane wrote:
> I've been looking into the possible performance consequences of that,
> in particular comparing snprintf.c to the library versions on macOS,
> FreeBSD, OpenBSD, and NetBSD. While it held up well in simpler cases,
> I noted that it was significantly slower on long format strings, which
> I traced to two separate problems:

> Perhaps there's a way to improve that
> without writing our own floating-point conversion code, but I'm not
> seeing an easy way offhand. I don't think that's a showstopper though.
> This code is now faster than the native code for very many other cases,
> so on average it should cause no real performance problem.

I kinda wonder if we shouldn't replace the non pg_* functions in
snprintf.c with a more modern copy of a compatibly licensed libc. Looks
to me like our implementation has forked off some BSD a fair while ago.

There seems to be a few choices. Among others:
- freebsd libc:
https://github.com/freebsd/freebsd/blob/master/lib/libc/stdio/vfprintf.c
(floating point stuff is elsewhere)
- musl libc:
https://git.musl-libc.org/cgit/musl/tree/src/stdio/vfprintf.c
- stb (as Alexander referenced earlier)
https://github.com/nothings/stb/blob/master/stb_sprintf.h

I've not benchmarked any of these. Just by looking at the code, the musl
one looks by far the most compact - looks like all the relevant code is
in the one file referenced.

Greetings,

Andres Freund