Re: DNS vs /etc/hosts

I'd start by comparing the /etc/nsswitch.conf files on the various
machines. If the second column contains "files" for passwd and hosts on
the fast machines, and "dns" on the slow machine, then change the slow
machine to "files" and see if it speeds up. That's an easy way to rule out
or condemn DNS.

If you change a machine to "files", make sure the /etc/passwd has at least
the user you intend to login as, and /etc/hosts has the hostnames.

Rick

Michael Fuhr
<mike(at)fuhr(dot)org>
Sent by: To
pgsql-general-own Lowell(dot)Hought(at)faa(dot)gov
er(at)postgresql(dot)org cc
Tino Wildenhain
<tino(at)wildenhain(dot)de>,
08/04/2005 02:29 pgsql-general(at)postgresql(dot)org
PM Subject
Re: [GENERAL] DNS vs /etc/hosts

On Thu, Aug 04, 2005 at 12:04:27PM -0500, Lowell(dot)Hought(at)faa(dot)gov wrote:
> Version 7.2 psql - /usr/bin/psql -d dbname -h machine1 ----
> connection time instant
> Version 8.0 psql - /usr/local/pgsql/bin/psql -d dbname -h machine1 ----
> conection time 15 seconds
> Version 8.0 psql - /usr/local/pgsql/bin/psql -d dbname -h ip.address
----
> connection time instant

Do the 8.0 connections to a name take exactly 15 seconds every time,
or does the time vary?

Have you done process traces on 7.2 vs. 8.0 to see what they're
doing differently? You mentioned that you were using Linux, so
something like "strace -o filename -r psql ..." should work (the
-r option should add relative timestamps to the trace so you can
see where the slowness is happening). As others have mentioned,
name resolution is generally done by libraries that aren't part of
PostgreSQL, so if two versions of PostgreSQL behave differently in
that respect then we need to find out what's different about them.
Have you used ldd to see what libraries each version of psql is
linked against? Are there differences aside from libpq?

Have you used a tool like dig, host, or nslookup to test whether
DNS indeed has a problem? That wouldn't answer why different
versions of psql apparently behave differently, but it should at
least tell us whether DNS is really a problem.

Have you used a sniffer like tcpdump or ethereal to watch DNS queries
and PostgreSQL connections?

--
Michael Fuhr

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