[Pdns-users] Performance issues

[Martijn Reening]

Hello everyone,

We are seeing very vague issues with our PowerDNS setup where certain
sequences of requests can cause full queues and dropped queries. Under
normal circumstances, the server can handle more than 10 kqueries/sec,
but when the bug is triggered, performance drops to 300-400 queries/sec.

There seems to be a correlation with the amount of domains that are
queried which return REFUSED. DNSSEC makes it easier to trigger this
problem, but disabling it does not make it disappear.

It is reproducible with both MySQL and PostgreSQL used as a backend, so
it doesn't seem to be an issue with the database. The schemas and
indices are correct. Our conclusions so far are that there is some kind
of bottleneck between PowerDNS and the database, but either are fast
enough under normal operation.

The slow requests are cached, because a second run within the TTL does
not cause slowness. We have already tried tuning these variables, and
while it does seem to help, it only masks the real issue.

We have run out of ideas where to look and what to tune. Perhaps anyone
here could help us further?

-- 
Regards,

Martijn Reening