[Pdns-users] no default cache-limit in pdns recursor?

Rudolph Bott rb at megabit.net
Tue Sep 25 21:16:43 UTC 2007

Rudolph Bott wrote:
> Hey List,
> does the powerDNS recursor limit itself to a reasonable amount of cache 
> entries if you do *not* set the relevant parameter in recursor.conf? We 
> had a setup with a recursor which ate up the memory of the server pretty 
> fast (within a couple of days). As soon as it reached the limit of 
> physical memory, the machine started to swap heavily and was rendered 
> almost useless (the recurser stoped responding to almost all queries or 
> returned failures). Unfortunatly this happend quite a while ago and I 
> don't have the munin graphs at hand right now. We solved the problem by 
> uncommenting and setting this in recursor.conf:
> #################################
> # max-cache-entries     If set, maximum number of entries in the main cache
> #
> max-cache-entries=500000
> We are using the standard packages available on Debian etch (should be 
> version 3.1.4-1)
> On top of that, i just noticed that apparently the recursor keeps more 
> than max-cache-entries in memory:
> stats: 429816539 questions, 503914 cache entries, 24045 negative 
> entries, 66% cache hits
> Mit freundlichen GrÌßen / with kind regards
> Rudolph Bott

Unfortunatly I kinda forgot to tell you what acutally bugged me about this situation:
As expected, the memory usage on the server raised continously until the limit of physically available memory was reached. At that point I would expect to see the usage of swap raising with the same steadiness. But instead it just explodes and seems to render the machine useless within just minutes (thats why I mentioned including the munin graphs).
As soon as I can find the time to recreate the problem in a non-production-environment, I will post my results to the list!

Mit freundlichen GrÌßen / with kind regards

Rudolph Bott
Megabit Informationstechnik GmbH
Karstr.25  41068 Moenchengladbach  Tel:02161/30898-0  Fax:-18
AG MG HRB 10141, GF: Dipl.-Ing. Thomas Tillig, Michael Benten

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