Hi, On 2018-10-01 19:52:40 -0400, Tom Lane wrote: > Thomas Munro <thomas.mu...@enterprisedb.com> writes: > > Mateusz Guzik was benchmarking PostgreSQL on FreeBSD investigating the > > kqueue thread and complained off-list about a lot of calls to memset() > > of size 256KB from dopr() in our snprintf.c code. > > > Yeah, that says: > > PrintfArgType argtypes[NL_ARGMAX + 2]; > > ... > > MemSet(argtypes, 0, sizeof(argtypes)); > > > PrintfArgType is an enum, and we define NL_ARGMAX as 16 if the OS > > didn't already define it. On FreeBSD 11, NL_ARGMAX was defined as 99 > > in <limits.h>. On FreeBSD 12, it is defined as 65536... ouch. On a > > Debian box I see it is 4096. > > > Is there any reason to use the OS definition here? > > Ouch indeed. Quite aside from cycles wasted, that's way more stack than > we want this to consume. I'm good with forcing this to 16 or so ... > any objections?
Especially after your performance patch, shouldn't we actually be able to get rid of that memset entirely? And if not, shouldn't we be able to reduce the per-element size of argtypes considerably, by using a uint8 as the base, rather than 4 byte per element? > (I wonder if this has anything to do with Andres' performance gripes.) It probably plays some role, but the profile didn't show it as *too* large a part. Greetings, Andres Freund
