Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-15
How Does RSC/MP Work?
The remainder of this subsection discusses how the RSC/MP products, the application
code, and appropriate operation combine to protect the application from these potential
failures.
How Availability Works
RSC/MP provides you with protection against the loss of a communications line or the
loss of the TDP. Availability of the server process is not protected by RSC/MP; instead,
the NonStop TS/MP subsystem provides that protection as described under NonStop
TS/MP and Highly Available Server Processes on page 6-4. Availability of the client
process is a function of the workstation capability and the language in which the client
is compiled.
Highly available RSC/ MP applications require significant involvement from
development and operations staff as described under Design Implications for RSC/MP
Applications on page 6-16. RSC/MP, however, does provide the following availability
features for you:
•
Transaction capability in the RSC/MP application programmer interface
•
Support for multiple data communications lines and multiple protocols
•
Replicated TDPs or initialized persistent TDPs
Transaction Protection
The ability to protect the database with transactions is critical to providing availability to
RSC/MP applications. Transaction begin, commit, and abort operations requested by
the client process using RSC/MP calls are converted to TMF calls on the server by the
TDP. A known point of consistency is thereby provided at the beginning of the
transaction, providing a safe point to resume operation if a critical component were to
fail, such as loss of the connection to the server, loss of the TDP, or loss of the server
process.
Note that TMF transactions begin and end in the TDP. It is up to the application
developer to trace the integrity of the transaction from the client process. Refer to
Design Implications for RSC/MP Applications
on page 6-16.
Multiple Data Communications Lines and Protocols
RSC/MP allows you to configure multiple data communications lines between your
client workstations and the HP server. These communications lines can be any
combination of TCP/IP, Failsafe TCP/IP, NETBIOS, or asynchronous lines, depending
on the connectivity of your workstations.
Following the loss of a data communications line, the client application can reconnect
to the server using an alternate communications line. This line might use a different
protocol. The TDP is notified of the loss of the line and performs any necessary clean
up on the server, including aborting any transactions that were started over the failed
line and terminating active sessions.