Bind 9.21: no more recursive clients

[Simon Waters]

Jeffery Jones wrote:
> 
>   This one wasn't obvious from reading the bind8 to 9 migration notes.

I think the default limit is the same, but BIND 9 is
substantially slower on single CPU machines, so maybe that is
why you hit the limit?

> In the meantime, I have bumped the recursive-clients limit to 5000.
> I may increase the limit to 20,000 after I do a bit more research.

I think it was limited originally because it took a few bytes
per outstanding query, I guess it could lead to memory
exhaustion if the performance was poor or memory limited. Memory
probably isn't such an issue at a nickle per megabyte or
whatever we are at these days.

You might want to keep an eye on performance at peak load.