[Pdns-users] PowerDNS Recursor Performance and Tuning

[Otto Moerbeek]

On Sun, Jan 16, 2022 at 09:39:01AM +0330, Hamed Haghshenas via Pdns-users wrote:

> Hello Dears,
> 
>  
> 
> I install PowerDNS Recursor 4.6.0 on CentOS Linux release 7.9.2009. and
> configure it as bellow for Iran IP address. I want use it in my ISP
> environment for large scale and lots of DNS requests. 

A more modern distribution might be better. What do you call lots?

> My Server have 4 core 2.6 Ghz (x64) and 8GB Ram (KVM Virtualization), I can
> apply more cpu or ram.

If you have 8G of RAM, likely the default cache sizes could be
enlarged (max-cache-entries for the record cache and
max-packetcache-entries for the packet cache)

Virtulization *could* be an issue, for example when the network
interface is virtualized in a way thet hinders performance. 

> Could you please help me that is my configuration correct? How many
> distributor-threads and threads should I use? (same as number of cpu cores
> or more).

Some comments inline below.

> 
> Need something to change, or any kernel optimization ?
>  
> 
> allow-from-file=/etc/pdns-recursor/IP-Iran-List.txt
> 
> setuid=pdns-recursor
> 
> setgid=pdns-recursor
> 
> local-address=127.0.0.1 172.16.1.186

If you are using NAT: this *kills* the performance. See
https://docs.powerdns.com/recursor/performance.html

> 
> any-to-tcp=yes
> 
> distribution-load-factor=1.25
> 
> pdns-distributes-queries=yes
> 
> distributor-threads=4

Depending on kernel version and other factors resuseports and multiple
distributor thread might work better or not, best to start with
reuserport=no and distributor-threads=1, test & measure and then
change to yes and 4 and compare performance on your actual setup.

> 
> dnssec=validate
> 
> dnssec-log-bogus=yes

If you see a lot ot bogus results this might impact performance

> entropy-source=/dev/random

This is likely slow, better use the default setting (leave it out).

> 
> logging-facility=0
> 
> lowercase-outgoing=yes

why? 

> max-tcp-queries-per-connection=10
> 
> quiet=no

This amount of logging will kill performance

> reuseport=yes

See above

> 
> threads=4

You might want to reduce it to 3 if you use 1 distribnutor thread, as
the total number of threads doing lots of work is distributor threads +
worker threads.  This is depedent on your cach hit ratios. Again:
try and measure.

	-Otto