Availability Guide for Application Design

Increasing the Availability of Tuxedo Applications
Availability Guide for Application Design—525637-004
5-3
High-Availability NonStop Tuxedo Applications
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Process pairs with initialized persistence
A process runs with a backup process that takes over if the primary process stops.
The backup process is preinitialized by a single checkpoint operation that occurs
when the primary process finishes its initialization phase.
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Process pairs with continual checkpointing
A process runs with a backup process that takes over if the primary process stops.
In this case, state information is continually checkpointed to the backup process so
that the backup process is able to take over processing from the point at which the
primary process stopped.
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File-system retries
If a failure occurs during an I/O operation, the file system has the capability to send
the I/O request again when function is restored. This technique is used, for
example, when sending nontransactional requests to the primary disk process and
the primary disk process fails.
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Transaction Management Facility (TMF) transactions
The transaction concept, as explained in Section 4, Data Protection and Recovery,
provides a known point of consistency for restart following a failure. Availability is
enhanced because the original transaction is backed out, leaving the database
exactly as the transaction found it. The new transaction can then execute as it
would have the first time.
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Client/requester context
The client process or requester process can save its execution context
immediately before starting a TMF transaction. The client or requester process can
use the saved context to restart a failed transaction.
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Process replication
More than one instance of the same program runs in separate processors to make
sure that there is always one copy of the process available if a processor failure
occurs. Server processes often execute this way to provide server availability in
addition to providing the ability to service a greater number of requesters and
balance the load.
The following subsection gives information on how these techniques provide
availability to NonStop Tuxedo applications.
High-Availability NonStop Tuxedo Applications
The NonStop Tuxedo product provides an environment for developing and executing
client/server applications that use a set of standard interfaces. The Tuxedo/WS portion
of the product ensures that client Tuxedo processes can run on a network workstation
in addition to running as a native client process on the server system itself. Any