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In this chapter, we looked at various features that COM+ provides to help develop scalable enterprise systems. These features include:
ODBC connection pooling and OLE DB resource pooling
Asynchronous method calls
There were more scalability features that were initially planned to be released with Windows 2000 but were ultimately dropped. Two such features were Component Load Balancing (CLB) and In-Memory Database (IMDB).
CLB will be included with a new product from Microsoft named AppCenter Server. With this technology, the client requests the AppCenter Server machine to activate an object. The COM+ Service Control Manager (SCM) on the AppCenter Server has been modified to handle the request locally or forward it to one of the specified set of machines based on dynamic input col-lected and analyzed by the load-balancing service. See Tim Ewald s article in Microsoft Systems Journal [Ewa-00] for more details.
With IMDB, a database can be completely loaded into memory. As the data is now accessed from the memory instead of a very slow (comparatively) hard disk, the throughput increases significantly. IMDB is very useful for those applications where reads vastly outnumber writes. See David Platt s book [Pla-99] for more details. The current status of IMDB can be found at the Microsoft website [MSDN-01].
A future release of COM+ (COM+ 1.x) will provide more services that will improve the scalability of a COM+ application. You will be able to configure the isolation level of a transaction (see Chapter 8) on a per-component basis. The release will also provide a mechanism to automatically and gracefully shutdown and restart a server process whose performance has degraded over time (for example, because of memory leaks). This feature is referred to as process recycling.
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