[Unbound-users] NOTIFY implementation to unbound

[Aaron Hopkins]

On Mon, 19 Oct 2009, Greg A. Woods wrote:
> However if _all_ the slaves are configured to send NOTIFY to Unbound
> (including, or excluding, the true master) then the last one to reload
> will cause a final flush of Unbound's cache and all will be well.
>
> Sorry I didn't make this concept clear before.  It was so obvious to me
> I forgot to mention it!  :-)

I'm not sure that this will be obvious to everyone or possible in many
topologies, and will lead to non-deterministic behavior that many people
will interpret as a bug in unbound.

More code could solve this, such as querying the SOA of all authoritative
servers for the zone(s) you were notified about and only flushing the
recursive servers' caches when they are all up-to-date.  However, this may
be better placed in an external daemon.

> BTW, performance considerations are secondary (or even tertiary).

It depends on how long each flush locks a big cache.  How many queries are
you willing to drop on the floor with each NOTIFY?  Are you willing to do so
with all of your recursive servers simultaneously?

                                     -- Aaron