Re: DNS vs /etc/hosts

Sorry to re-reply, but I had a much simpler idea.  From the client machine
that is slow to connect, type the command "nslookup hostname1".  If it
takes 15 seconds.  If it does, DNS is the problem.

Rick

pgsql-general-owner@postgresql.org wrote on 08/04/2005 03:01:31 PM:

> 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@fuhr.org>

>              Sent by:
To
>              pgsql-general-own         Lowell.Hought@faa.gov

>              er@postgresql.org
cc
>                                        Tino Wildenhain

>                                        <tino@wildenhain.de>,

>              08/04/2005 02:29          pgsql-general@postgresql.org

>              PM
Subject
>                                        Re: [GENERAL] DNS vs /etc/hosts

>

>

>

>

>

>

>
>
>
>
> On Thu, Aug 04, 2005 at 12:04:27PM -0500, Lowell.Hought@faa.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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