Random slow queries

[Mike Chesney]

Running Bind 9.6.1-P3

We run authorative DNS for 60k+ zones.  One one network where we two dns
servers both running the same hardware on Centos 5.4

We see slow dns responses : example

for i in {1..250}; do dig example.com @localhost | grep "Query time:"; done;

Sometimes they'll all come back w/ a 0msec response .  But every few runs we
see.
; Query time: 501 msec
;; Query time: 111 msec
;; Query time: 0 msec
;; Query time: 0 msec
; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 1461 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 441 msec
;; Query time: 0 msec
;; Query time: 0 msec
;; Query time: 0 msec

This is just a snapshot, most other entries are all 0.  This doesn't happen
on any of our other dns servers.  Load is pretty low on this machine around
.3   4gb ram.  Named consumes about 15% of memory and 4% of cpu.  Not sure
where to look next.
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