Resolver cache redesign
This is a meta issue to collect current problems & ideas what to do about it.
Current known problems:
- LRU cleaning can get state into a weird state: #2744
- Cache cleaning can block things, and is generally a mess: #3261, #4383 (closed)
- Negative answers from e.g. a random subdomain attack can push out useful things: #2495, #1831
- ADB vs. cache size is hardcoded and nobody knows if this is optimal or not: #2483 (closed), #2405
- Sizing is hard to get right: #614
- Cache is child-centric: #3311
- RRSIGs and not tightly bound to respective RR: #3396
- Data structures referenced by RBTDB are a mess: #4356, #3403, #3405