Unbound Serve expired; cache hit rate reducing with time

[Yorgos Thessalonikefs]

Hi Andy, Issac,

Maybe you are both hitting a variation of
https://github.com/NLnetLabs/unbound/issues/994.
Namely, Unbound when resolving will try to update the cache with new 
data even if the stale data would have been more useful.
There is ongoing work to make Unbound more careful with replacing cached 
content when serve-expired is used.

Best regards,
-- Yorgos

On 01/08/2024 04:46, Andy Lemin via Unbound-users wrote:
> Hi,
> 
> I have a similar experience, where prefetch seems to poison the cache 
> with negative responses.
> 
> This is a good read; 
> https://unbound.docs.nlnetlabs.nl/en/latest/topics/core/serve-stale.html 
> <https://unbound.docs.nlnetlabs.nl/en/latest/topics/core/serve-stale.html>
> 
> Can any one clarify a parameter combination which allows immediate cache 
> responses, and which tells prefetch to always ignore negative responses?
> 
> I wonder if taking the advice of the above article (and being mindful of 
> this https://github.com/NLnetLabs/unbound/issues/533 
> <https://github.com/NLnetLabs/unbound/issues/533> it is possible to get 
> this working). Just can’t figure out how to force prefetch to ignore 
> negative responses.
> 
> Please share your results :)
> Andy.
> 
> 
>> On 31 Jul 2024, at 20:33, sir izake via Unbound-users 
>> <unbound-users at lists.nlnetlabs.nl> wrote:
>>
>> 
>> Hi
>> I have installed unbound version: 1.20.0 on a FreeBSD 14 server. This 
>> was working fine until the server lost internet connectivity to the 
>> upstream internet provider. Prior to this the average cache hit rate 
>> on the server was 99.0% with only 1% recursive replies.
>> Part of my unbound.conf file is shown below
>>
>> server: prefetch: yes serve-expired: yes
>> # serve-expired-ttl: 0
>>  # serve-expired-ttl-reset: no
>> After loss of internet average cache hit rate has reduced to 14% 
>> whiles recursive queries is showing 86% (still internet is not restored)
>> My expectation is
>> Caching server should continue to serve expired and keep the cache hit 
>> rate high because the serve-expired-ttl is default
>> (meaning it should continue serving cached content until upstream is 
>> restored).
>> My observation is the opposite. Is there anything I am missing? How 
>> can i ensure that the caching server will continue serving cache data 
>> several days after upstream
>> internet is lost
>> Regards
>> Isaac
>>
>>
>>