CST(33)-Messaging and Queuing

Every Distributed Application Development needs a Message Oriented Middleware. MOM is a key piece of middleware that is absolutely essential for a class of Client/Server products. MOM allows general purpose messages to be exchanged in a Client/Server system using message queues. Applications communicate over networks by simply putting messages in queues and getting messages from queues.

MOM messaging and queuing allows clients and servers to communicate across a network without being linked by a private, dedicated, logical connection. The clients and servers can run at different times. Messages does not impose any constraints on an application’s structure i.e. if no response is required none is sent.

MOM products provide their own NOS services – including hierarchical naming security and a layer that isolates applications from the network. They use virtual memory on the local OS to create their queues. Most messaging products allow the sender to specify the name of the reply queue.

MOM enabled programs do not talk to each other directly, so either program can be busy, unavailable or simply not running at the same time. A program can decide when it wants to retrieve a message off its queue. Messaging queues ae very versatile. They can be used to create one-to-many or many-to-one relationships. Many clients can send requests to one server queue. The messages are picked off the queue by multiple instances of the server program that are concurrently servicing the clients. The server instances can take off the messages either on First in first out basis or priority basis.

The servers can also use message filters to throw away the messages they don’t want to process or they can pass it to other servers. Most also provide persistent and nn persistent queues. Persistent messages are slower but they can be recovered in case of system crash. A message can be local or remote. System administrators can usually specify the number of messages a queue can hold and the maximum size. 
CST(33)-Messaging and Queuing Reviewed by 1000sourcecodes on 21:40 Rating: 5
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