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

On 2018-10-03 13:40:03 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On 2018-10-03 13:31:09 -0400, Tom Lane wrote:
> >> I do not see the point of messing with snprintf.c here.  I doubt that
> >> strfromd is faster than the existing sprintf call (because the latter
> >> can use ".*" instead of serializing and deserializing the precision).
>
> > I'm confused, the numbers I posted clearly show that it's faster?
>
> Those were in the context of whether float8out went through snprintf.c
> or directly to strfromd, no?

I measured both, changing float8out directly, and just adapting
snprintf.c:

> snprintf using sprintf via pg_double_to_string:
> 16195.787
>
> snprintf using strfromd via pg_double_to_string:
> 14856.974 ms
>
> float8out using sprintf via pg_double_to_string:
> 16176.169
>
> float8out using strfromd via pg_double_to_string:
> 13532.698

So when using pg's snprintf() to print a single floating point number
with precision, we get nearly a 10% boost. The win unsurprisingly is
bigger when not going through snprintf.c.

Greetings,

Andres Freund