The architecture described in the first few pages is interesting. With a title like "Application Architecture", I was mislead into thinking this chapter was more about the application, but rather it is the fundamental pieces that Oracle has built to interface with various applications. I am a bit cautious about the apparent benefits of scaling vertically and horizonatally; obviously, everyone wants the option to scale if needed. While Vertical scaling seems to be the most common solution, I am a bit discouraged how hard Oracle PR has pushed Horizontal scaling in the form of RAC, almost as if it were a panacea for all functional and performance issues. But I digress.
I was excited to see the section "How Oracle Net Services work". As with previous technical material in this document, I was again disappointed with the high-level summary provided, instead of the real nuts and bolts. Ironically, in light of the coverage, I was surprised to find mention of "industry-standard higher level protocols"; seems to be a bit of bandwidth to advertise how compliant they are. I would think the reader would be more interested in the details that specifically relate to how Oracle talks to itself, leaving the underlying transports systems for a book of another scope. The whole point of an API is to abrstract out the details that one does not really care about. So I was glad to move on to the next section about the Listener and Services.
Yet my concern did not stop there. Check out this quote from the Listener section:
When multiple databases or instances run on one computer, as in Real Application Clusters, service names enable instances to register automatically with other listeners on the same computer. A service name can identify multiple instances, and an instance can belong to multiple services. Clients connecting to a service do not have to specify which instance they require.
Wow. Ok, so RAC runs on one computer?!? Since when? I have to admit that I am greatly impressed by how PMON communicates not only with the local listener, but also remote listeners on different computers. But there is no mention of local_listener, remote_listeners or how those play a huge role. Worse, "services" have not even been covered in sufficient detail yet; it would probably help to point out that while a service may map to multiple instances, all such instances must be part of the same database. Regardless, I have to repeat that I am duly impressed by the slickness we call "services" (head nod to Jeremy Schneider for his paper on making it a little more public). If only more beans were spilled out of the can here in the Concepts Guide.
And then the chapter ends right there. Egads! 6 pages covers Application Architecture?!?