Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-18
Availability Through Pathsend
Operational Concerns
To ensure application availability, the operations staff must:
•
Decide whether to run the TDP as a process pair with initialized persistence. A
process pair with initialized persistence can take over in less time than a replicated
TDP.
•
Retain the TDP configuration following a total failure of the TDP by maintaining a
command file that will correctly configure the TDP at startup. This command file is
required following failure of both the primary and the backup TDP or following
failure of a TDP process that has no backup.
•
Decide whether to configure two connections between the workstation and the
server. If a single-configured connection fails, then the client process will have to
wait until the problem is corrected before reconnection attempts will succeed. If two
connections are configured, then the client can reconnect to the server
immediately using the alternate connection.
•
For applications that use TCP/IP, decide whether to run the TCP/IP process as a
process pair. When run as a process pair, the backup process is available for
reconnections if the primary process fails.
•
Run the TCP/IP TELNET process as a process pair to ensure that system
management applications can access the RSC/MP application if a processor fails.
Availability Through Pathsend
The Pathsend facility provides a procedure call interface and a link manager function.
The procedure call interface enables compiled requester processes that run on an HP
NonStop system to make requests of NonStop TS/MP servers using the Pathsend
procedure calls. These requesters can be written in any supported language, such as
C, C++, COBOL85, and TAL.
This subsection introduces the Pathsend facility and its availability features. First, it
establishes how the applications that use the Pathsend interface normally function and
includes a skeletal work session. It goes on to describe how availability is maintained
even if critical components fail and how a typical work session is affected. Finally, it
explains what the application designer or developer needs to consider to take full
advantage of these features.
How Does the Pathsend Facility Work?
The link manager function is provided by LINKMON (D and G-series) or the ACS
subsystem. They are used to facilitate access between the Pathsend requester and the
NonStop TS/MP server classes. The link manager works with the PATHMON process
to provide the link-management functions. A link manager function runs in each
processor and is responsible for all the Pathsend requesters executing in its processor.