Page #83 (Chapter 12 - IIS Applications and Microsoft Transaction Server)

	Chapter 12 - IIS Applications and Microsoft Transaction Server
	Visual Basic Developers Guide to ASP and IIS
	A. Russell Jones

Copyright 1999 SYBEX Inc.

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	How Can MTS Help You?

	Beyond all the features and advantages already mentioned, possibly the biggest advantage that MTS provides is the capability to update a component without stopping the server. When IIS uses a DLL, it "locks" the DLL into memory. To replace the DLL, you must stop IIS. During development that's no problem at all, but in a production environment it may be impossible to stop the server simply to update one component for your application. Other users may be in the middle of critical operations in other applications running on that server. If you stop the server, you destroy all the sessions.

	Using the Internet Service Manager, you can mark your applications so that they run in a separate process space than the root Web application. If you do that, you can release DLL locks on components used exclusively by your application by unloading the application. That helps, but not enough. If any other application is using the DLL, unloading your application won't release all the locks, and you'll still be unable to replace the component. If you run the component under MTS, you can release all references and replace the component without having to stop the applications. Of course, depending on the application's needs, you may still affect the application if you update components while the applications are running.

	The second largest advantage is that MTS maintains objects in memory. Throughout this book, I've tried to hammer home the first rule of Web programming: Get in, get the data, get out. Almost anything that can help you do that is worth doing, and you'll see immediate benefits, either in application responsiveness or in application scalability. Unfortunately, few things that you can do will improve both responsiveness and scalability. MTS does slow down application initialization, so the first people to reach your application will have to wait longer for the application to load. After it's loaded, though, you'll be able to scale much better with MTS than without it.

	Finally, MTS lets you group functionality and control access to functionality through role-based security. In many Web applications, where users access the site anonymously, this kind of security won't do you any good. On intranet sites, where all the people accessing the application can be authenticated through the network, MTS security is a blessing. Instead of having to set individual properties or write code, you can break your application into interfaces and assign permissions to the interfaces.