Re: vacuum slowed by syslogd

Michael Adler <adler@pobox.com> writes:
> On many occasions, I've noticed that some PostgreSQL activity takes
> far longer than it previously did and that disabling syslogd addresses
> the symptoms.
> ...
> This evidence normally indicates a name resolution issue, but I'm not
> sure how to test for that beyond using "hostname -v -i".

I looked in Red Hat's bugzilla for similar issues, and found a mention
that syslogd tries to reverse-lookup the address it gets each message
from.  A delay there could act as you describe.  At least in recent RH
releases, you can start syslogd with the "-x" switch to disable this
lookup --- does that exist in Debian, and if so does it help?

I would expect any comparable resolution delays on the client side to
occur only once when a backend is started, not once per message, since
we only openlog() once per backend.  So a delay on the syslogd side
seems a likely theory.

Something else you could do to investigate is to test whether syslogd
can log messages from other clients during these 10-second delays.
If it's hung trying to resolve a name, presumably messages from other
clients would get delayed too.

            regards, tom lane