[Feature request] Ability to serve expired records in the cache by type.

[Benno Overeinder]

Not sure why prefetch option does not work for you without enabling 
serve-expired.  How did you test the prefetch option?

 From the manual page:

prefetch: <yes or no>
If yes, message cache elements are prefetched before they expire to keep 
the cache up to date. Turning it on gives about 10 percent more traffic 
and load on the machine, but popular items do not expire from the cache.

Prefetch causes active queried cached items to be prefetched when they 
are at 10% of their TTL.  If the cache item is not queried during this 
time, the item will expire.

For serve-expired feature, there are two alternatives available, see the 
documentation: 
https://unbound.docs.nlnetlabs.nl/en/latest/topics/core/serve-stale.html


-- Benno


 > On 8 May 2023, at 00:31, alpominth--- via Unbound-users 
<unbound-users at lists.nlnetlabs.nl> wrote:
 >
 > Here in my tests, prefetch option only works when serve-expired is 
enabled.
 >
 > Here is one of my configuration files:
 >
 > server:
 > interface: 127.0.0.1
 > interface: ::1
 > port: 53
 > cache-max-ttl: 21600
 > cache-min-ttl: 21600
 > cache-max-negative-ttl: 21600
 > val-bogus-ttl: 0
 > infra-host-ttl: 21600
 > prefetch: yes
 > serve-expired: yes
 > serve-expired-ttl: 2592000
 > delay-close: 10000
 > chroot: ""
 > username: "permcache"
 > directory: ""
 > pidfile: ""
 > do-not-query-localhost: no
 > module-config: "validator cachedb iterator"
 >
 > cachedb:
 > backend: redis
 > # redis-server-host: ::1
 > # redis-server-port: 6379
 > redis-server-password: "blah123"
 > redis-server-path: "/opt/permcache/db/redis-server.sock"
 > redis-timeout: 5000
 >
 > forward-zone:
 > name: "."
 > forward-addr: ::1 at 10053
 >
 >
 > /\ Prefetch works, but the negative and host cache are cached for 1 
month when prefetching is enabled, I would like to set a very short 
caching time for them, 1 or 2 days.
 >
 > Options for controlling the expired host cache and negative cache 
separately would be a very good idea, as negative and host entries would 
have different TTLs.
 >
 > The options could be:
 >
 > serve-expired-negative-ttl: <seconds>
 > serve-expired-infra-host-ttl: <seconds>
 >