Pathway/iTS TCP and Terminal Programming Guide

Introduction to TCP and Terminal Application

Programming

Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001

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Data Integrity

If your database is corrupted by a hardware or software failure, you might need weeks to

isolate and then correct the problem. Because an inaccessible or inconsistent database

can have a dramatic, adverse effect on business operations, the Transaction Management

Facility (TMF) subsystem, provided in the NonStop™ TM/MP product, was developed

as a way of ensuring database consistency. The TMF subsystem, which works with

NonStop™ TS/MP, protects the entire database from catastrophic system failures by

maintaining an audit trail of database changes (that is, transactions); an audit trail is also

commonly known as a transaction log. You can use the audit trail to rebuild the

database in the event of a hardware or software failure.

The design of Pathway servers supports the integrity of individual transactions and

therefore transaction processing protection as a whole. Because the requester/server

model allows a clear division of processing functions, application programmers can

code each server program to handle a specific set of transaction types: for example,

checking an account balance, entering a new customer, or updating the parts inventory.

The server processes service their transactions by performing the same set of tasks over

and over again. In this way, a valid transaction is defined as a specific set of tasks both

by the requester program and within the server logic.

If for any reason a server is unable to complete all tasks involved in processing a

transaction, it can abort the transaction and thereby maintain the transaction’s integrity.

The server does not have to wait for the requester to abort the transaction.

Fault Tolerance

Because OLTP systems automate core business operations and deliver key business

services, companies depend on OLTP applications to stay up and running—even if a

hardware or software component fails.

NonStop™ Himalaya systems, which are specifically intended for online transaction

processing, are designed to remain continuously available during the hours when

transactions are being entered and business is being conducted. Typically, a NonStop™

Himalaya system can continue processing despite the failure of any single software or

hardware component within that system. This ability is referred to as fault tolerance.

In the Pathway enviroment, automatic fault tolerance (that is, fault tolerance that does

not require any additional programming effort on your part) is provided by the use of

process pairs and the actions of the PATHMON process, the TMF subsystem, and the

terminal control process (TCP).

In the Guardian operating environment, the functions and tasks of an application are

performed by processes, which are running programs. A process pair consists of a

primary process, which does some specific function in the overall work of the

application, and a secondary (backup) process, which remains ready to take over if the

primary process fails. During processing, the primary process keeps the backup process

informed of what it is doing (for example, sending a request) by means of special

interprocess messages, in an activity called checkpointing. Through checkpointing, the

backup process has enough information to take over and continue if the primary process

fails.