[Pdns-users] Using pdns-recursor on a network with high latency.

bert hubert bert.hubert at netherlabs.nl
Fri Sep 18 08:40:06 UTC 2009

On Fri, Sep 18, 2009 at 9:16 AM, Sten Spans <sten at blinkenlights.nl> wrote:
> As far as I know there currently is no way to improve powerdns-recursor's
> behaviour, short of modifying the source. I think Bert would appreciate a
> well tested patch which improves the behaviour, although only if it doesn't
> hurt lookup performance. It might be reasonable to add an "high-latency"
> option, or even better use the initial root-hints lookup and prehaps later
> ones to auto-tune a reasonable timeout value.

Sten, Andre,

I'm currently looking in to this and I see why this has not been fixed
- the timeout mechanism is rather crude, and may in fact not even be
doing exactly what it is supposed to be doing. It is supposed to
deliver a '1000ms' timeout right now, but it appear it is only doing
that on average, sometimes doing a 0ms timeout and sometimes a 2000ms

So I suspect this would be hard for a third party to patch. I'm
looking into this to see if there IS a bug, and if there could be a
tunable timeout somewhere.

On a related note, both BIND and djbdns decide to keep on sending
questions until they get an answer, behaviour I do not find to be
warranted for normal operations. PowerDNS effectively tries not to be
an amplifier, and is thus slightly more prone to sending timeouts. In
effect, PowerDNS delivers a lower percentage of timeouts to clients in
the 'normal case', so this is not a problem.


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