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
1-5
Other Fundamentals of NonStop™ Himalaya
Systems
Both the PATHMON process and the TCP can be configured as process pairs to support
Pathway applications. When the PATHMON process is configured as a process pair,
you are ensured the ability to control and monitor OLTP system operation even if the
primary PATHMON process fails. When a TCP is configured as a process pair and the
primary TCP fails, terminals controlled by the TCP can still be used.
Pathway server classes provide additional fault tolerance by allowing requests to be
rerouted to surviving server processes in a server class if one server process fails.
Besides process pairs and server classes, fault tolerance in a Pathway application is
ensured by the PATHMON process, the TCP, and the TMF subsystem. Using
information stored in the PATHMON configuration file, the PATHMON process
automatically restarts processes at their initialization level after a failure, allowing these
processes to resume work immediately.
For requesters written in SCREEN COBOL that use the TMF subsystem, the TCP
automatically restarts processing at the transaction boundary (for example, at the
BEGIN-TRANSACTION statement) after a failure. In addition to restarting processing,
the TCP directs the TMF subsystem to back out any incomplete or partial transaction
and restore the database to its pre-failure state of consistency. By both restarting
processing at the transaction boundary and directing the TMF subsystem to recover a
transaction, the TCP ensures that the application and the database are synchronized and
ready to continue processing.
Other Fundamentals of NonStop™ Himalaya Systems
Besides data integrity and fault tolerance, the Pathway environment also provides the
high performance and low cost, system security, scalability, and distributed processing
of NonStop™ Himalaya systems.
High Performance and Low Cost
The more transactions your system can process (preferably without degrading response
time), the lower the cost of each transaction. The Pathway environment supports fast
response time and high system throughput by allowing:
•
Component processes in a Pathway application (for example, requester and server
processes) to reside and execute concurrently in different processors of a multi-CPU
system or even a network. This is called multiprocessing.
•
More than one Pathway application to run in a NonStop™ Himalaya system.
•
More than one requester program to execute in the TCP at the same time. This is
called multithreading. Multithreading permits the processing of multiple and
different transactions concurrently and permits multiple users to perform similar
tasks—for example, order entry—simultaneously.
The Pathway environment also supports fast response time and high system throughput
by allowing the replication of processes and programs and the distribution of processes.
For example: