|
|
|
|
|
|
What Are Nested and Forwarded Service Requests
Nested Requests
A powerful feature of the BEA Tuxedo system is that it allows services to act as clients and call other services. Nesting is limited to two levels, which works particularly well in a 3-tier client/server architecture, that is, a system that comprises a presentation logic layer, a business logic layer, and a database layer. In such a system, the presentation layer is used to formulate a request for a particular business function that involves one or more queries to a database. Because nesting is limited to two levels, it does not degrade performance.
Nested Service Requests
One benefit of using nested requests is that doing so enables you to keep your code small and reusable, such that each piece performs a limited task. However, if the services in your system are distributed across several servers, nested requests can lead to poor performance. While a nested request is being processed, the original service (that is, the service that issued the nested request) must wait for a response before continuing. Until a response is received, the original service cannot process another request. As a result, messages can get backed up in the request queue for the server on which this service resides.
Example of a Nested Service Request
A customer uses a cash machine to transfer money from her savings account to her checking account. A BEA Tuxedo application performs the work necessary to transfer the money. First, on behalf of the customer, the client issues a request for a service called TRANSFER, and the request is placed on a queue for a server that provides that service. Next, the TRANSFER service requests two other services, WITHDRAW and DEPOSIT, which are processed by a second server. The WITHDRAW and DEPOSIT services return responses to the TRANSFER service. Finally, TRANSFER sends a response to the client's response queue. When the client retrieves the response from the queue, the system displays a message on the screen of the cash machine, notifying the customer that the transfer is complete.
Forwarded Requests
One alternative to nesting service requests is called request forwarding. Instead of processing a client's request, a service can pass the request to another service. The second service, also, can either process the request or pass it to another service.
Forwarded Service Requests
There is no limit to the number of times a request can be forwarded. Because a service that forwards a request does not need to wait for a reply from the service receiving the request, forwarding, unlike nesting requests, does not block servers. Forwarding, however, is not supported by the X/OPEN protocol X/ATMI, which may be a problem in some applications.
See Also
|
|
|
|
|
|
Copyright © 2000 BEA Systems, Inc. All rights reserved.
|