Thank you for some clue in this. So, I assume changing log_destination (from syslog to stderr) was a way around it to override log_min_messages when the -d option is specified?
I am checking with the vender, SIOS, on what scenarios LifeKeeper would start up PostgreSQL with the -d5 option.
> From: tgl@sss.pgh.pa.us
> To: kong_mansatiansin@hotmail.com
> CC: pgsql-admin@postgresql.org
> Subject: Re: [ADMIN] log_min_messages=debug5, despite an explicit setting to warning on postgresql.conf
> Date: Sun, 23 Dec 2012 12:21:12 -0500
>
> Kong Man <kong_mansatiansin@hotmail.com> writes:
> > We ran into a production issue during our maintenance window when I switched over LifeKeeper/PostgreSQL nodes from one to another. We noticed that the database was 1000 times slower than it usually is, then realized that the log_min_messages setting was set to 'debug5' for no reason.
>
> How was the postmaster started? From memory, "-d5" on its command line
> would do that, and would not have been overridable from postgresql.conf.
>
> regards, tom lane