[Pdns-users] PowerDNS authoritative server random timeouts

[Netsons - Federico Chiacchiaretta]

Hi Klaus,
I excluded network issues for a while, so I focused my analysis
on MySQL.

Simply running a 'show processlist' during one of the random timeouts
brought me to the solution: I found a lot of queries in state 'Waiting
for query cache lock', so I completely disabled query_cache in MySQL
configuration.

I made the change on Sep 19th, and never had a timeout since then.

I hope this can be useful for anyone experiencing the same issue.

Best,

-- 
Federico Chiacchiaretta
System Administrator
Netsons S.r.l. - https://www.netsons.com


On Thu, 2019-09-26 at 07:23 +0200, Klaus Darilion wrote:
> I think, first you should find out if there is a problem with
> PowerDNS 
> or the network - or inbetween.
> 
> If this happens regularly, just use tcpdump to caputre all DNS
> traffic 
> to a file (rotate files, keep only X files and choose X to not fill
> your 
> complete hard disk).
> 
> Or even simpler - just capture with tcpdump the loopback traffic
> (your 
> own check script) with -i lo.
> 
> Make sure you really see the requests to PDNS, but no answers. Of
> maybe 
> there are answers, but much too late.
> 
> The problem may be that PDNS reads fromt he socket to sloow. Then
> the 
> socket fills up and you have packet loss (tools like netstat can
> report 
> this).
> 
> Also monitor the PDNS statistics. Ie read:
> https://blog.powerdns.com/2014/12/11/powerdns-graphing-as-a-service/
> 
> Then watch the number of outstanding queries, maybe send them every
> second.
> 
> regards
> Klaus