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

>>>>> "Andres" == Andres Freund <andres(at)anarazel(dot)de> writes:

Andres> Hm, stb's results just for floating point isn't bad. The above
Andres> numbers were for %f %f. But as the minimal usage would be about
Andres> the internal usage of dopr(), here's comparing %.*f:

Andres> snprintf time = 1324.87 ms total, 0.000264975 ms per iteration
Andres> pg time = 1434.57 ms total, 0.000286915 ms per iteration
Andres> stbsp time = 552.14 ms total, 0.000110428 ms per iteration

Hmm. We had a case recently on IRC where the performance of float8out
turned out to be the major bottleneck: a table of about 2.7 million rows
and ~70 float columns showed an overhead of ~66 seconds for doing COPY
as opposed to COPY BINARY (the actual problem report was that doing
"select * from table" from R was taking a minute+ longer than expected,
we got comparative timings for COPY just to narrow down causes).

That translates to approx. 0.00035 ms overhead (i.e. time(float8out) -
time(float8send)) per conversion (Linux server, hardware unknown).

That 66 seconds was the difference between 18s and 1m24s, so it wasn't a
small factor but totally dominated the query time.

--
Andrew (irc:RhodiumToad)