Optimizing Performance

Because the Microsoft Exchange client polls installed extensions every time a context change occurs, Microsoft Exchange can exhibit decreased performance or response time if several extensions are installed. In particular, performance can be affected when displaying menus, sending and receiving messages, or selecting different messages and folders. This performance degradation can be caused by extensions that respond to events that are not applicable to the functionality they provide. It can also be caused by extensions that take a long time to respond when Microsoft Exchange invokes their methods.

When developing an extension, you can reduce the impact on the performance of Microsoft Exchange by keeping the following programming guidelines in mind:

• Register your extension only for contexts that are applicable to it. This can be done by placing the appropriate values in the context map in the EXCHNG.INI file or the registry. The context map designates contexts in which an extension will participate. Although specifying a context map is optional, it is highly recommended. If you don't specify a context map, an attempt will be made to install your extension in all contexts and it will be loaded at all times. For more information about context maps, see Registering Extensions.
• Register your extension only for interfaces that are applicable to it. This can be done by placing the appropriate values in the interface map in the EXCHNG.INI file or the registry. Although specifying an interface map is optional, it is highly recommended. The interface map prevents Microsoft Exchange from making calls to IUnknown::QueryInterface for interfaces that are not supported. This can improve the performance of context creation and application startup.
• Optimize functions that handle various events received by your extension. For example, event-handling functions should minimize the use of any time-consuming calculations, loops, lookups, and file input and output.