Slow/no response

[Ian Carr-de Avelon]

Ralf Hildebrandt wrote:
>On Thu, Oct 21, 1999 at 04:21:30PM +0100, Ian Carr-de Avelon wrote:
>> I have a problem that looking up hosts on our system occasionally becomes
>> slow and then searches start to fail. This even affects local zones. The
>> problem occures at times of high congestion on the net, which leads me to 
>
>If the net is congested, how should BIND's answers come through?
I am obviously not being clear enough here. I don't mean that my own
net is congested, or my link to the Internet, I mean that the international
links are congested. The inability to resolve is exactly the same on the 
name server itself as on the rest of the local net. I would expect that 
distant zones would resolve progresively slower and then start to time out.
I would expect resolutions from cached zones to remain fast (obviously
it is difficult to be sure that cached information has not exceeded its
time to live. I would expect that resolution of zones for which the 
server is the primary would always remain fast. So if I type:
host www.emit.pl 
on the server and that never resolves, something has gone wrong. This
happens after named has been running for hours/days without problems. If I
kill named, I hear a large amount of disk activity for a few seconds 
and a newly started named will resolve local addresses as expected 
for a few minutes, before the same problem occures. 


S Trefethen wrote:
>Just a thought, but you might want to check to see if your server is
>swapping.  *ANY* swapping can slow dns down considerably, lots of swapping
>will severely impair a dns box.
What I see on the system is:

	CPU states:  0.7% user,  0.3% system,  0.0% nice, 99.1% idle
	Mem:   30716K av,  27404K used,   3312K free,   6460K shrd,   2304K buff
	Swap: 142408K av,   5400K used, 137008K free                 12312K cached

	  PID USER     PRI  NI  SIZE  RSS SHARE STAT  LIB %CPU %MEM   TIME COMMAND
	  846 Web        3   0  7080 6528  1076 S       0  0.0 21.2  32:51 roxen
	12957 root       1   0  2108 1460   412 S       0  0.1  4.7   0:21 named
Obviously there is a very little bit of swap used there, but that seams to be
typical of the way Linux manages memory. I don't hear any thrashing of the 
disk. I can maybe play with setting named to a negative nice value, but 
it is not that the program really stops. Strace   shows that there is a 
sort of heartbeat going on, but it never answers the resolver.

Yours
Ian