[Unbound-users] cache size usage.

W.C.A. Wijngaards wouter at NLnetLabs.nl
Mon Sep 6 08:46:24 UTC 2010

Hash: SHA1

Hi Hugo,

The message cache contains the 'message formats', with DNS rcodes and
validation status (like the header part of 'dig' output).  The rrset
cache contains the RR data (like the data part of 'dig' output).
- From experiment we think rrset cache should be about 2x the size of the
msg cache.

For you, I timidly suggest, msg-cache-size: 256M and rrset-cache-size:
512M.  If you also do dnssec validation, increase the key cache and neg
cache too, say 128M each.

If the parameters are not used, defaults (4M) are used.  The cache grows
until it hits the limit that is configured.  Then it stops growing.
Well, unbound stops asking for more memory, but your system memory
allocator may not be able to satisfy the requests for different sizes
and thus incur a 2x overhead on top. (my suggestion with a 2x overhead
comes to about 2Gb, leaves you with spare room; it could be possible to
increase memory further).

Best regards,

On 08/23/2010 03:20 PM, hugo hugoo wrote:
> Hello,
> I plan to use UNBOUND on an HP linux server (1CPU quad core - 3 GB)
> I have the following questions about the cache size.
> On my present DNS software, the cache size is present in the
> configuration file and is put to 2Gb.
> In UNBOUND, I see in the configuration file the following parameters:
> msg-cache-size ==> what is the meaning of this parameter?  What do I
> have to put as value for my specific hardware?
> rrset-cache-size ==> what is the meaning of this parameter?  What do I
> have to put as value for my specific hardware?
> Last question, what happens if these parameters are not used?
> Is the cache always growing and giving a problem when no more memory is
> available?
> Thanks in advance for your help.
> Hugo,
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