BIND occassional slowdowns

[Daniel Ryslink]

Hello,

I have run into a problem with one of our caching DNS resolvers running 
currently BIND 9.3.2 on FreeBSD 4.11. The problem manifests itself as 
occassional slowdown in response from the average 1-3 ms to sometimess well 
over 3000ms. The anomaly always lasts only a few seconds, and after that the 
normal operation resumes.

Though the DNS responses are never lost, such a delay usually causes 
timeouts on our mailservers that use this machine for resolving, usually 
resulting in delayed mail, application timouts and other unpleasant 
consequences.

I believe that the hardware is sufficient, because the named process mostly 
takes 7-10% of the CPU and about 450MB (out of 1G) of available RAM. The 
server usually has about 300 simultaneous caching queries at one time. I 
also checked the various OS limits like maxprocs, max open files, 
nmbclusters, bandwidth usage, and the machine does not seem to be lacking 
any resource.

The nameserver serves both as authoritative and caching nameserver (I know 
it's not recommended, and we are working on moving all the zones away to 
make it purely caching resolver).

If anyone experienced similar problems, all advices are most welcome.

Thank you in advance.

Best regards,
Daniel Ryslink