Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > I wonder if this fsync for PostgreSQL messages is some change made to
> > Linux syslog.
>
> You're missing the point: by default syslog fsyncs *all* messages.
> You can turn this off on a per-output-file basis by putting "-" on the
> desired lines of the syslog config file. It has nothing whatever to do
> with Postgres.
>
> The fact that you don't see any fsync calls doesn't prove anything. How
> about O_SYNC or O_DSYNC flags when opening the output files? That would
> be the natural way to implement it given the spec.
Well, doing a grep for sync, I see:
(2) grep -i -4 SYNC syslogd.c/* Flags to logmsg(). */#define IGN_CONS 0x001 /* don't print on console
*/#defineSYNC_FILE 0x002 /* do fsync on file after printing */#define ADDDATE 0x004 /* add a date to
themessage */#define MARK 0x008 /* this message is a mark *//* Types of actions */-- char *lp;
lp = msg + msglen; for (p = msg; p < lp; p = q + 1) { flags = SYNC_FILE | ADDDATE; /* fsync
fileafter write */ if (parse_pri(&p, &pri)) { if (pri &
~(LOG_FACMASK|LOG_PRIMASK)) pri = DEFSPRI; } else {--
f->f_name)); } } else { f->f_warning = 0;
if (flags & SYNC_FILE) (void)fsync(f->f_file); }
break; case F_USER:-- p += snprintf(p, sizeof(buf) + buf - p, ": %s",
strerror(errno)); dprintf(("%s\n", buf)); logmsg(LOG_SYSLOG|LOG_ERR, NULL, buf, p - buf,
LocalHostName, ADDDATE|SYNC_FILE);}
Which basically shows one fsync, no O_SYNC's, and setting of the flag
only for klog reads.
> strace'ing syslogd on my HPUX box shows that it doesn't issue explicit
> fsync calls either, but I don't know of any way to tell whether it's got
> the log files opened O_SYNC.
>
> BTW the Linux man page says specifically that their syslogd tries to be
> compatible with BSD.
Yes, I saw that too, but maybe not in this area. It is all in one file,
so here is the FreeBSD version:
http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.sbin/syslogd/syslogd.c?rev=1.59.2.28&content-type=text/x-cvsweb-markup
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square,
Pennsylvania19073
