Subscription leasing, garbage collection and scalability

[David Hull <dmh@tibco.com>]

I believe the upshot of the previous exchange is, if you expect a 
subscriber to make a lot of subscriptions, the lease time had better be 
long or indefinite.  In fact, from the producer's point of view, if you 
expect there to be a lot of subscriptions, period, the lease time had 
better be long or indefinite.

In other words, the only method that WS-BN provides for garbage 
collection of subscriptions should be effectively disabled precisely 
when it is most likely to matter.

I think the problem here is that WS-BN addresses subscription leasing 
and not garbage collection per se.  This doesn't mean that it should try 
to provide all possible means of garbage collection, only that it should 
specifically point out a need, allow for as wide a range of solutions as 
is feasible, and point to subscription leasing (a la WS-RL) as one 
solution.  This is essentially the same road we went down with topics.

The more I consider leasing of individual subscriptions, the more 
potential technical issues I see.  Obviously, none of them is 
insurmountable -- they have all been addressed and solved in other 
contexts.  But each carries weight for the potential implementor.  I'm 
willing to drill down on these a bit if needed, but I'm hoping we can 
avoid this and take a higher-level decision that leasing of individual 
subscriptions, while useful in some contexts, should not be required or 
be the only possible GC mechanism.

With that provisional assumption, the immediate question becomes how can 
we allow for session-based garbage collection without adding undue 
weight to the WS-BN framework.  Sessions have their own technical issues 
and implementation weight.