Availability Guide for Application Design

What Is Application Availability?
Availability Guide for Application Design—525637-004
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Design Program Modules for Availability
Applications That Run in the NonStop Tuxedo Open
Environment
The NonStop Tuxedo product provides an open interface for developing or porting
applications for execution on NonStop systems. The combination of this product and
the NonStop architecture bring the NonStop fundamentals, including availability, to
applications that use this standard interface.
The NonStop Tuxedo product provides for highly available applications using the
client/server model. Server processes typically run on an NonStop server, while client
processes typically run on client PCs or workstations. Server processes are highly
available because they run under the supervision of a PATHMON process. The
PATHMON process ensures that a server is always available by creating replicated
server processes and restarting servers that fail. The PATHMON process itself runs as
a process pair to ensure that it is always available to monitor your application.
A workstation handler (WSH) process provides a gateway to the NonStop system. It
provides database consistency and application availability through starting and ending
TMF transactions on behalf of the client process on the workstation. The WSH process
is neither a process pair nor an immediately persistent process. Workstation listener
(WSL) processes, however, are immediately persistent and start WSH processes
whenever necessary.
Section 5, Increasing the Availability of Tuxedo Applications, contains a discussion of
availability issues in NonStop Tuxedo applications.
Applications That Run in the Pathway Transaction
Processing Environment
Applications that run in the Pathway transaction processing environment also support
client/server applications but use traditional NonStop interfaces. The server part of the
application runs on an NonStop server while the client process runs on a PC,
workstation, or host other than an NonStop host. Requester processes that typically
control terminals run on an NonStop server in the same Expand network as the server
process; although conceptually the same as client processes, these processes are
called requesters for historical reasons.
At the heart of every application in the Pathway transaction processing environment is
the PATHMON process, which supports the server part of the application. It monitors
the server to ensure that the server process is always running. PATHMON is a process
pair that ensures that monitoring continues even if the primary PATHMON process
fails.
The availability features of the client or requester depend on the interface. The
following interfaces each provide facilities to support highly available applications:
•
RSC/MP
•
Pathsend interface to NonStop TS/MP
•
Pathway/iTS