how to configure SERVFAIL/weird answer caches

[Petr Špaček]

Hello,

could someone share details of how SERVFAIL cache works and how it can 
be configured? Pointers to places in code where I can tweak constants 
are also welcome.

Background:
I'm trying to configure Unbound to cache everything for one day 
(`cache-min-ttl: 86400`). The intent is to create a "snapshot" in 
Unbound's cache, and then I plan to re-query that snapshot from another 
piece of software repeatedly.

I cannot find anything about SERVFAIL cache in unbound.conf or at 
https://unbound.docs.nlnetlabs.nl/en/latest/ .

My question can be generalized to "how do I make Unbound to cache 
everything including broken answers for a specified period of time"?

Thank you!

-- 
Petr Špaček  @  Internet Systems Consortium