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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)lists(dot)postgresql(dot)org, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru>
Subject: Re: Performance improvements for src/port/snprintf.c
Date: 2018-10-03 18:01:35
Message-ID: 3316.1538589695@sss.pgh.pa.us
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Andres Freund <andres(at)anarazel(dot)de> writes:
> So when using pg's snprintf() to print a single floating point number
> with precision, we get nearly a 10% boost.

I just tested that using my little standalone testbed, and I failed
to replicate the result. I do see that strfromd is slightly faster,
but it's just a few percent measuring snprintf.c in isolation --- in
the overall context of COPY, I don't see how you get to 10% net savings.

So I continue to think there's something fishy about your test case.

BTW, so far as I can tell on F28, strfromd isn't exposed without
"-D__STDC_WANT_IEC_60559_BFP_EXT__", which seems fairly scary;
what else does that affect?

regards, tom lane

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