Date: Sun, 12 Aug 2018 06:26:15 +0000
From: Noah Misch <noah@leadboat.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Chapman Flack <chap@anastigmatix.net>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: libpq should not look up all host addresses at once
Message-ID: <20180812062615.GA2619236@rfd.leadboat.com>
References: <4913.1533827102@sss.pgh.pa.us>
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 <14647.1533839578@sss.pgh.pa.us>
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On Thu, Aug 09, 2018 at 02:32:58PM -0400, Tom Lane wrote:
> Chapman Flack <chap@anastigmatix.net> writes:
> > On 08/09/2018 11:05 AM, Tom Lane wrote:
> >> So I think what this code should do is (1) look up each hostname as it
> >> needs it, not all at once, and (2) proceed on to the next hostname
> >> if it gets a DNS lookup failure, not fail the whole connection attempt
> >> immediately.  As attached.
> 
> > Would it be worth the complexity to be a little async about it,
> > fling a few DNS requests out, and try the hosts in the order the
> > responses come back?
> 
> It would be nice if an async connection request didn't have to block during
> DNS lookups ... but I don't know of any portable library API for async DNS
> requests

https://c-ares.haxx.se/ is the async DNS API that I've experienced.  It works
well if you really need such a thing, but I haven't needed it in libpq.