Caching only servers

[Kevin Darcy]

If you're that short of memory, then it's going to be a narrow margin
between being too aggressive and keeping too much data resident, on the
one hand, plus hitting up the CPU all the time to do cleaning, versus,
on the other hand, not cleaning aggressively enough and having your
virtual memory fill up with unused or little-used cache. You could play
with it and try to hit the "sweet spot" between those 2 extremes. You
could also try playing with max-cache-ttl (the evil twin of
max-ncache-ttl), which will give your nameserver more cleaning
opportunities, at the expense, of course, of increasing query latency
times for data that were cleaned out of the cache prematurely.


- Kevin

"Georgeson, Evan [NCSUS Non J&J]" wrote:

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> Thanks Kevin...I've since uncovered these wonderful little tidbits.
> See, we use QIP and in so doing we have some systems with ISC BIND
> with the majority using Lucent-BIND. Now, 2 weeks ago our deployment
> dept removed 9.1.3 and went to Lucent-BIND. These serving problems
> just started last week so I suspect this...considering our caching
> servers only have, don't laugh, 256 MB of RAM (my laptop has 512!) I
> believe the Lucent BIND added some memory overhead that pushed an
> already overtaxed system(s) over the edge. Today we've since reverted
> to 9.1.3. We will be adding more memory, of course, but do you think
> that there is any reason to re-visit my cleaning-interval? Do you
> have a suggestion on a new value? Also, is there a Lucent-BIND
> support group similar to this? Thank you again for your time and
> advice.
>
> Evan
>
> - -----Original Message-----
> From: Kevin Darcy [mailto:kcd at daimlerchrysler.com]
> Sent: Tuesday, July 16, 2002 5:19 PM
> To: BIND Users (bind-users at isc.org)
> Subject: Re: Caching only servers
>
> "Georgeson, Evan [NCSUS Non J&J]" wrote:
>
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> > Hi,
> >
> >         I'm suffering some bizarre symptoms on my two cache
> > servers.  For some reason, they stop servicing internal requests
> > and then
> > restart after a few minutes. Could there be a load issue?
>
> Yes :-)
>
> > I'm going to give
> > you a list of the named.conf options can I get someone to check
> > them  for validity and confirm correct or no?? Thank you very much
> > if you  can help or advise.
>
> Your cleaning-interval is set to 4 minutes. That seems a little
> rabid. Did you increase the frequency to try to keep your memory
> usage down? If you have sufficient memory, I'd relax the cleaning
> interval. By touching your memory pages this frequently, you may be
> forcing them to be resident more often and actually *hurting* your
> memory situation.
>
> > Also, is it logged when nslookup queries return nxdomain or
> > servfail,  e.g., queries.log??
>
> No, I do not believe this is available in the query log.
>
> NXDOMAIN is a fairly routine reponse code; clients ask for
> non-existent names all of the time (especially when they are
> configured with searchlists, grrrrr....)
>
> SERVFAIL is not so common, but in general, whatever is causing the
> SERVFAIL condition is being logged by your nameserver in some other
> way. Unfortunately, there are many different things which can give
> rise to a SERVFAIL -- it's kind of a catch-all category.
>
> You can try turning up the logging for various categories and/or
> turning on debugging, if you want more information on these
> conditions, but be aware that this will drive up your resource
> consumption, which you may not want to do at this time.
>
> - - Kevin
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