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

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Performance improvements for src/port/snprintf.c
Date: 2018-09-27 01:18:14
Message-ID: 20180927011814.kpncoksuqq3gy44s@alap3.anarazel.de
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Hi,

On 2018-09-26 17:57:05 -0700, Andres Freund wrote:
> snprintf time = 1324.87 ms total, 0.000264975 ms per iteration
> pg time = 1434.57 ms total, 0.000286915 ms per iteration
> stbsp time = 552.14 ms total, 0.000110428 ms per iteration

Reading around the interwebz lead me to look at ryu

https://dl.acm.org/citation.cfm?id=3192369
https://github.com/ulfjack/ryu/tree/46f4c5572121a6f1428749fe3e24132c3626c946

That's an algorithm that always generates the minimally sized
roundtrip-safe string output for a floating point number. That makes it
insuitable for the innards of printf, but it very well could be
interesting for e.g. float8out, especially when we currently specify a
"too high" precision to guarantee round-trip safeity.

Greetings,

Andres Freund

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