Random slow queries

Stacey Jonathan Marshall Stacey.Marshall at Sun.COM
Thu Feb 25 11:01:55 UTC 2010


On 02/24/10 18:50, Mike Chesney wrote:
> 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 <http://example.com> @localhost 
> | grep "Query time:"; done;
Centos is a time-sharing system right.  I wonder if your time-share is 
up and your simply being scheduled off CPU - the network communication 
is an opportunity for the scheduler to do that.
Try adding a sleep and see if your results smooth out - more 0 msec and 
less msec total.

for i in {1..250}; do sleep 0.5; dig example.com <http://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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