Re: stats collector process high CPU utilization

Benjamin Minshall <minshall(at)intellicon(dot)biz> writes:
> Tom Lane wrote:
>> It's sounding like what you had was just transient bloat, in which case
>> it might be useful to inquire whether anything out-of-the-ordinary had
>> been done to the database right before the excessive-CPU-usage problem
>> started.

> I don't believe that there was any unusual activity on the server, but I
> have set up some more detailed logging to hopefully identify a pattern
> if the problem resurfaces.

A further report led us to realize that 8.2.x in fact has a nasty bug
here: the stats collector is supposed to dump its stats to a file at
most every 500 milliseconds, but the code was actually waiting only
500 microseconds :-(. The larger the stats file, the more obvious
this problem gets.

If you want to patch this before 8.2.4, try this...

Index: pgstat.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v
retrieving revision 1.140.2.2
diff -c -r1.140.2.2 pgstat.c
*** pgstat.c 26 Jan 2007 20:07:01 -0000 1.140.2.2
--- pgstat.c 1 Mar 2007 20:04:50 -0000
***************
*** 1689,1695 ****
/* Preset the delay between status file writes */
MemSet(&write_timeout, 0, sizeof(struct itimerval));
write_timeout.it_value.tv_sec = PGSTAT_STAT_INTERVAL / 1000;
! write_timeout.it_value.tv_usec = PGSTAT_STAT_INTERVAL % 1000;

/*
* Read in an existing statistics stats file or initialize the stats to
--- 1689,1695 ----
/* Preset the delay between status file writes */
MemSet(&write_timeout, 0, sizeof(struct itimerval));
write_timeout.it_value.tv_sec = PGSTAT_STAT_INTERVAL / 1000;
! write_timeout.it_value.tv_usec = (PGSTAT_STAT_INTERVAL % 1000) * 1000;

/*
* Read in an existing statistics stats file or initialize the stats to

regards, tom lane