[CentOS] DJBDNS: very weird dnscache issue

Wed Jan 14 18:47:17 UTC 2015
Boris Epstein <borepstein at gmail.com>

Lucian,

So far here is the best we could find out:

https://bugzilla.redhat.com/show_bug.cgi?id=1084747

Testing to see if this is the solution; so far it seems to be.

Cheers,

Boris.


On Tue, Jan 13, 2015 at 2:49 PM, Nux! <nux at li.nux.ro> wrote:

> Use BIND. How the times have changed. :-)
>
> PS: I'm also curious for a solution.. for when djbnostalgia hits me.
>
> Lucian
>
> --
> Sent from the Delta quadrant using Borg technology!
>
> Nux!
> www.nux.ro
>
> ----- Original Message -----
> > From: "Boris Epstein" <borepstein at gmail.com>
> > To: "CentOS mailing list" <centos at centos.org>
> > Sent: Tuesday, 13 January, 2015 15:53:28
> > Subject: [CentOS] DJBDNS: very weird dnscache issue
>
> > Hello all,
> >
> > We have put a DNS server online running  DJBDNS v1.06
> > (ndjbdns-1.06-1.el6.x86_64) on a 64-bit CentOS 6.6 server. We have done
> > some limited testing on the machine which it passed - i.e., dnscache was
> > talking to tinydns, the queries went through fine, etc.
> >
> > As soon as we put it online subjecting it to live load the following
> > happened:
> >
> > 1) Within a short time period (about a minute) the dnscache process
> reached
> > the CPU utilisation level of 100%.
> >
> > 2) The process would then die reporting the following message to the log:
> >
> > dnscache: BUG: out of in progress slots
> >
> > NOTE: Random sampling indicates that at no point sampled did the load
> > exceed 200 requests per second. In tests conducted earlier the DNS server
> > successfully demonstrated speeds in tens of thousands of requests per
> > second.
> >
> > We then proceeded to edit the following parameters in the dnscache.conf
> as
> > they seemed to be the only ones that seemed relevant: DATALIMIT and
> > CACHESIZE. They are described as limints (in bytes) on the total data
> > memory allocation and cache, default values are 80000000 and 50000000
> > respectively.
> >
> > Playing with these demonstrated some highly counterintuitive results:
> >
> > 1) Setting the values lower (say, an order of magnitude lower) made the
> > dnscache process run longer.
> >
> > 2) Shortening the relative gap between the two values (for instance,
> > setting DATALIMIT at 52000 and CACHE at 50000) made it run for about an
> > hour vs about 1 minute, load seeming to be about the same.
> >
> > 3) Running it with DATALIMIT not set was possible though it eventually
> > failed anyways.
> >
> > 4) Running it with CACHESIZE not set was not possible at all.
> >
> > So the issue is currently still not resolved and we are stuck.
> >
> > Any advice will be much appreciated.
> >
> > Cheers,
> >
> > Boris.
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