Memory utilisation problem on busy bind resolver

[Dennis Perisa]

Hi folks,

We are running a number of BIND 9.7.3-p3 caching nameservers.  In the
last couple of months, we've observed the memory utilisation of named
increasing at a steady rate of 1-2% per day on our busiest resolver
with no indication of subsiding - on occasion, there have been large
step increases of 1 GB or so.

All our other resolvers are configured identically but are behaving
themselves with memory utilisation remaining at fairly constant
levels.

I've looked at all the named logs until my eyeballs have almost fallen
out of my head but am unable to determine the cause of this.  So I'm
taking a step back and hoping to get some advice - what else can I do
to find the cause of this?  Or is it something I simply need to live
with?

We're looking at measures such as periodic cache flushes, and tuning
max-cache-size, max-cache-ttl and max-cache-nttl params to limit
memory usage, but this may only be treating the symptom and costs us
extra cpu cycles.

Regards
Dennis