snprintf.c hammering memset() - Mailing list pgsql-hackers

From Thomas Munro
Subject snprintf.c hammering memset()
Date
Msg-id CAEepm=3VF=PUp2f8gU8fgZB22yPE_KBS0+e1AHAtQ=09schTHg@mail.gmail.com
Whole thread Raw
Responses Re: snprintf.c hammering memset()  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: snprintf.c hammering memset()  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
Hello hackers,

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?

-- 
Thomas Munro
http://www.enterprisedb.com


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