Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-25
How Pathway/iTS Works
A TCP executes screen programs and coordinates communication between such a
program, its terminal, and the server processes it calls on. The TCP automatically runs
multiple screen programs concurrently and interleaves the processing of different
transactions from multiple terminals. These features of TCP are keys to simplifying
application programming.
Using the intelligent device support (IDS) facility of the TCP, access to the Pathway
server classes is increased to include a wide range of intelligent devices.
The following sequence shows a skeletal outline of a typical TCP application when
operating normally. Familiarity with this sequence will be helpful in understanding the
recovery requirements and procedures described later in this section.
1. The COBOL program begins a transaction and gets a transaction identifier. The
TCP automatically checkpoints the relevant state information to its backup
process.
2. The program formulates a request and sends it to the server process.
3. If the requester is not yet linked with a server process, the PATHMON process
establishes a link with one member of the selected server class, and the send
operation proceeds using Guardian interprocess communication. If the requester is
already linked with a server, then the send proceeds without involvement from the
PATHMON process. Note that lost messages between the requester and server
are automatically retried by the file system.
4. The server processes the request and replies to the requester.
Figure 6-6. Components Supporting Pathway/iTS Applications
Server
Server Class
PATHMON
TCP
TCP
Terminals
Automated Teller
Machines
IDS
Database
Pathway/iTS
NonStop TS/MP
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