[Pdns-users] Spikey response times in powerdns recursor

[bert hubert]

On Wed, Mar 17, 2010 at 11:16:40AM +0000, Simon Bedford wrote:

> >Mar 17 11:57:02 [5] bbc.co.uk.: Resolved 'bbc.co.uk.' NS ns1.bbc.co.uk. to: 132.185.132.21
> >Mar 17 11:57:02 [5] bbc.co.uk.: Trying IP 132.185.132.21:53, asking 'bbc.co.uk.|A'
> >Mar 17 11:57:04 [5] bbc.co.uk.: timeout resolving
> 
> It never used to happen before 23/12/09 though looking at our graphs
> and as you say this happens for at least 5 domain names that we
> monitor (some of which are our own and some external).

bbc.co.uk still has a nameserver that is down, so having that domain resolve
slowly every once in a while is to be expected.

You've indicated you've occasionally seen 500ms lookups times for
google.com, but I have not heard of any other problems.  

google.com takes between 0 and 100ms to resolve in my tests. 

> >This matches the expectations.
> 
> Doubling overnight and acceptable to have 2 second look up times??
> This is definitely not something that would be acceptable to our
> customers for valid domains...

These measurements from dnsscope are for _all_ domain names, not just valid
domains. Please do not think that I recommend 2 second lookup times. 

The reality is that a huge number of domains have unresponsive nameservers.
Your graph indicates that 1% of queries takes between 1024 and 2048 msec to
resolve at night, and this is entirely to be expected.

A doubling of *average* response times, but still in the <40ms range, is
entirely to be expected on a server that is relatively idle at night.

	Bert