TMF Introduction (G06.24+)

TMF Application Programming

HP NonStop Transaction Management Facility (TMF) Introduction—522414-001

5-2

The Requester/Server Model

In the Pathway application environment, applications consist of two types of

programs: requesters and servers. This design allows application logic to reside

near the resources it manages. For example, presentation logic is located near

workstations or terminal devices; database logic resides in server programs near

the database. The requester sends a request to the server, which performs the

requested action and then replies to the requester. The requester and server may

reside on the same processor or on different processors. Requesters and servers

communicate by using the Guardian file system or the message system that is part

of the NonStop Kernel operating system. For a sample application based on the

requester/server model, see Designing Applications for the Pathway Environment

on page 5-9.

Even though transactions are typically controlled by the requester, most servers

need transaction control to back out (abort) a transaction if errors occur.

Servers must always reply to requesters to indicate whether they were able to

perform the requested work. The reply satisfies TMF requirements for committing

or aborting transactions. If a server does not reply to a requester with the status of

the transaction, the requester is left with an outstanding request to the server and

cannot complete the transaction.

Accessing and Locking Data

TMF automatically manages database access and locking of audited files. It generally

operates in the same way, regardless of the API or programming language used to

access the database. The syntax the applications use to access a database, however,

varies, depending on the programming language and the type of database.

The issues involved in accessing and locking data include:

•

Controlling transaction isolation

•

Accessing SQL data

•

Accessing Enscribe data

•

Managing deadlock

Note. In distributed applications, the client/server model is often used. This model

extends the requester/server model. In general, but not always, in this model the client

process resides on a workstation and the server process resides on a second workstation,

minicomputer, or mainframe system. Communication takes the form of request and reply

pairs, which are initiated by the client and serviced by the server. Client/server computing

is often used to connect different types of workstations or personal computers to a host

computer system by means of communication protocols.