Broadening the scope of the negative connection cache

[Marc VanHeyningen]

Gerald (Jerry) Carter sed:
>> The obvious solution would be to migrate the negative 
>> connection cache to be stored in a different way, probably
>> as a TDB file.  This would allow every child process to share
>> the failure information.
>
>I believe the easiest way to achieve this is simply to
>use the gencache API and set a 60 second TTL on entries.

Sounds good, but a 60 second TTL seems too short to me.  Attempting 
to find a host and having it fail to respond can take a significant 
fraction of 60 seconds in some (admittedly unusual) cases.

Probably the best system is an adaptive one, which increases the 
TTL of the negative entry the longer the target remains inaccessible,
but that's more complexity than this situation really warrants.

Marc