Microsoft Transaction Server
Microsoft Transaction Server (MTS) was software that provided services to Component Object Model (COM) software components, to make it easier to create large distributed applications. The major services provided by MTS were automated transaction management, instance management (or just-in-time activation) and role-based security. MTS is considered to be the first major software to implement aspect-oriented programming.[1]
MTS was first offered in the
COM+ is still provided with
Architecture
A basic MTS architecture comprises:
- the MTS Executive (mtxex.dll)
- the FactoryWrappers and Context Wrappers for each component
- the MTS Server Component
- MTS clients
- auxiliary systems like:
- runtimeservices
- the Service Control Manager (SCM)
- the Microsoft Distributed Transaction Coordinator(MS-DTC)
- the MSMQ)
- the COM-Transaction Integrator (COM-TI)
- etc.
COM components that run under the control of the MTS Executive are called MTS components. In COM+, they are referred to as COM+ Applications. MTS components are in-process
MTS inserts a Factory Wrapper Object and an Object Wrapper between the actual MTS object and its client. This interposing of wrappers is called interception. Whenever the client makes a call to the MTS component, the wrappers (Factory and Object) intercept the call and inject their own instance-management algorithm called the Just-In-Time Activation (JITA) into the call. The wrapper then makes this call on the actual MTS component. Interception was considered difficult at the time due to a lack of extensible metadata.[1]
In addition, based on the information from the component's deployment properties, transaction logic and security checks also take place in these wrapper objects.
For every MTS-hosted object, there also exists a Context Object, which implements the IObjectContext interface. The Context Object maintains specific information about that object, such as its transactional information, security information and deployment information.
MTS does not create the actual middle-tier MTS object until the call from a client reaches the container. Since the object is not running all the time, it does not use up a lot of system resources (even though an object wrapper and skeleton for the object do persist).
As soon as the call comes in from the client, the MTS wrapper process activates its Instance Management algorithm called JITA. The actual MTS object is created "just in time" to service the request from the wrapper. And when the request is serviced and the reply is sent back to the client, the component either calls SetComplete()/SetAbort(), or its transaction ends, or the client calls Release() on the reference to the object, and the actual MTS object is destroyed. In short, MTS uses a stateless component model.
Generally, when a client requests services from a typical MTS component, the following sequence occurs on the server :
- acquire a database connection
- read the component's state from either the Shared Property Manager or from an already existing object or from the client
- perform the business logic
- write the component's changed state, if any, back to the database
- close and release the database connection
- vote on the result of the transaction. MTS components do not directly commit transactions, rather they communicate their success or failure to MTS.
It is thus possible to implement high-latency resources as asynchronous resource pools, which should take advantage of the stateless JIT activation afforded by the middleware server.
References
- ^ ISBN 978-0-201-73411-9. Retrieved 4 October 2011.