7.3 + kqueue + apache/php + DNS lookup problem

[Matthew Seaman]

On 01/10/2011 02:18, Doug Barton wrote:
>> Does this happen when httpd tries to do DNS resolution for, say, an
>> > incoming connection to the web server (e.g. trying to resolve the
>> > incoming IP address of the client to an FQDN), or is it happening within
>> > some PHP code (assuming PHP is installed/used as an Apache module)
>> > that's trying to do DNS resolution of some kind?

> It's a php module doing a lookup for the hostname of the back-end mysql
> server.

Hmmm... Is this a function of DNS traffic being via UDP?  Presumably
you're not seeing the same sort of delays when eg. apache connects to
mysql via TCP.

Hard to think of another UDP protocol you could use to test -- SNMP
perhaps?  Or somehow forcing the DNS traffic to go via TCP?  Tricky to
make that happen when the resolver is on localhost.  Of course, since
DNS will only fall back to TCP after trying UDP, that's going to be even
slower overall than your current situation, but the point here is to
examine the truss output for timing details specifically around where
the TCP query is issued.

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
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PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
JID: matthew at infracaninophile.co.uk               Kent, CT11 9PW

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