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On 06/11/2014 06:05 PM, Janczuk, Tomasz wrote:
> Process level isolation is more costly than sub-process level isolation
> primarily due to larger memory consumption. For example, CGI has worse
> cost characteristics than FastCGI when scaled out. But the example closer
> to Marconi¹s use case is database systems: I can¹t put my finger on a
> single one that would isolate queries executed by its users using
> processes.

That is certainly a good point. However not all database systems would 
entirely isolate users from each other. In some a user could overload 
the system with lots of slow queries and impact the responsiveness of 
the database to other users. In extreme cases you could cause deadlocks 
in the database.

> Sub-process multi-tenancy is a not an easy problem, but it is not one that
> cannot be solved, especially in the context of a messaging system. A
> messaging system exposes a set of operations that is very well defined and
> constrained. The cost of these operations can be relatively easily
> assessed a priori and managed accordingly to provide a secure multi-tenant
> platform.

I agree it can be done. Not sure whether I agree that its relatively 
easy to do so - but then it is all relative! :-)

Thanks for the responses though, they have been helpful in improving my 
understanding.

--Gordon.