Availability Guide for Application Design

Increasing the Availability of Tuxedo Applications
Availability Guide for Application Design—525637-004
5-6
Availability of NonStop Tuxedo Applications
process to make sure that enough servers are available to handle the workload,
control of the distributor process pairs that provide load balancing among the
servers, and server process restart capabilities.
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A link manager process that uses information in the bulletin board to provide
linkage between a WSH or a native client process and a server.
Transaction support through TMF provides transactions that are atomic, consistent,
isolated, and durable as described in Section 4, Data Protection and Recovery.
NonStop Tuxedo Skeletal Work Session
The following sequence shows the skeletal outline of a typical NonStop Tuxedo
application when operating normally. Familiarity with this sequence will be helpful in
understanding the recovery requirements and procedures described later in this
subsection. For simplicity, the following outline assumes context-free servers and
synchronous response. Note that conversational servers can also be implemented, as
can asynchronous communication.
1. On request from the client process, the WSL process establishes a session
between the client and a WSH process.
2. The client process requests to start a transaction. The WSH process converts the
ATMI or TX function call into a Transaction Management Facility (TMF) procedure
call that invokes the TMF product. TMF in turn supplies a new transaction identifier.
3. The client process makes a request for a service. The link manager process uses
the information in the bulletin board to locate an appropriate server process—one
that contains the requested service—and establishes a link between the WSH
process and the server process.
4. The server processes the request—invoking other servers if necessary—and
replies to the WSH process.
5. The WSH process replies to the client process.
6. The client makes additional requests (Step 3 through Step 5).
7. The client process requests the end of the transaction. The WSH process converts
the ATMI or TX function call into a TMF procedure call that invokes TMF to carry
out the two-phase commit protocol.
8. The client issues additional transactions (Step 2 through Step 7).
Availability of NonStop Tuxedo Applications
NonStop Tuxedo applications depend on a combination of availability techniques to
keep the application online. TMF transactions provide a known point of consistency for
application restart following a failure. Process replication ensures that a server process
is always available. Process pairs keep the supervisor process always available and
also keep the NonStop TCP/IP processes on the server system available, if so
configured. Transaction context is saved by the WSH process and might also be kept