I particularly liked the way Clara summarized the problem with tier-based architectures:
GigaSpaces argues that tier-based architecture is the nemesis to
linear scalability. In fact, the architecture itself is the bottleneck,
not unoptimized component. This is because in a tier-based
architecture, as scability patches are introduced, the communication
between the tiers become more complicated and expensive. The complex
interaction between tiers and between physical machines in the
deployment cause problems with latency and data consistency. Possible
problems with tier-based architecture are bottlenecked access to the
database, bottlenecked access to a centralized messaging provider,
messaging overhead, network latency, inefficient clustering, and
unreliable failover recovery. GigaSpaces addresses each of those
problems by providing a platform that enables space-based architecture.
Couldn’t say it any better.