performance aspects libunbound

[Michael Ströder]

HI!

Developer colleagues are testing libunbound instead of
libasyncresolv for validating DNSSEC RRs later.

Currently even without DNSSEC RRs they experience a significant higher 
CPU load.

Some questions:
- Is libunbound using caching when used as stub resolver?
- Can caching be deactivated? (local resolver on same machine)
- Any general hints for performance optimization for high load?

Ciao, Michael.