Recursive bind becomes unresponsive with high load

Michael Brunnbauer brunni at
Thu Mar 31 17:32:21 UTC 2016

Hello Tony,

On Thu, Mar 31, 2016 at 05:08:43PM +0100, Tony Finch wrote:
> Michael Brunnbauer <brunni at> wrote:
> >
> > I am using bind on a server that does massive crawling with a multithreaded
> > Java app. This server occasionally has to do lookups for hosts in our local
> > zone - for which it is not authoritative - and those lookups tend
> > to fail when the load is high (e.g. >1000 recursing clients). This suggests
> > some kind of congestion.
> Have you tried adjusting the clients-per-query and max-clients-per-query
> options?

I just tried 

        clients-per-query 250;
        max-clients-per-query 1000;

and it did not help. I noticed a drop in the number of recursing clients and
the number of queries/s when a lookup failed for the local zone but named
logged no special messages in the syslog.

Is is possible that is this connected to rndc stats? I will stop doing
rndc stats for a while to test (it currently runs every minute).

BTW: I also excluded packet loss as cause of the problem.


Michael Brunnbauer

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