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Re: Why don't we allow DNS names in pg_hba.conf?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jon Jensen <jon(at)endpoint(dot)com>
Cc: Andreas Pflug <pgadmin(at)pse-consulting(dot)de>, "Marc G(dot) Fournier" <scrappy(at)postgresql(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Why don't we allow DNS names in pg_hba.conf?
Date: 2006-01-02 19:06:38
Message-ID: 8029.1136228798@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Jon Jensen <jon(at)endpoint(dot)com> writes:
> On Mon, 2 Jan 2006, Tom Lane wrote:
>> Can you demonstrate that this is actually a serious concern next to the
>> total time spent launching a backend?  I can't measure any real change
>> in total time for "psql -l" when log_hostname is enabled, which should
>> be a comparable hit.

> The difference is negligible when using a UNIX socket (of course) or names 
> listed in /etc/hosts. But it's certainly slower in my tests if you really 
> use DNS. On a run of 1000 connections doing "psql -l", it takes 18.89s 
> without the DNS lookup for log_hostname, and 31.5s with. Or run as a 
> one-off, it's 0.032 to 0.041s.

Um --- I was testing a local-loopback connection, but now that I look at
the nsswitch.conf setup, it was going to /etc/hosts for that case.
Coming across the network so that a real DNS lookup is forced, there
seems to be a difference of about 4ms (note this is with a local DNS
daemon).  I don't think that's significant.  If it is, you've got other
performance problems anyway, and should switch to pooled connections to
reduce the number of backend launches.

			regards, tom lane

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