Availability Guide for Application Design

Availability in the Pathway Transaction-Processing
Environment
Availability Guide for Application Design—525637-004
6-21
Availability of Pathsend Applications
To keep the application available to the users of a specific instance of a requester, the
requester must run as a process pair. The following paragraphs describe the level of
application availability provided by:
•
TMF transactions
•
A Pathsend requester that runs with neither persistence nor as a process pair
•
A Pathsend requester with immediate persistence
•
A Pathsend requester that executes as a process pair
Transaction Protection
TMF provides support for starting, committing, and aborting transactions. The TMF
product is able to roll back transactions to keep the database consistent in the event of
any kind of failure and provide a known point of consistency for restart. Pathsend
procedure calls that are made within a transaction carry the transaction identifier with
them so that the actions performed by the receiving server processes become part of
the transaction.
Following processor failure, or if the server process or requester process stops, then:
1. TMF backs out the transaction, leaving all data in a known consistent state.
2. The requester process starts the transaction again using state information saved
when the transaction was first started.
3. The requester process replays the transaction either by rerunning user input that
was saved before the transaction aborted, or by prompting the user to reenter the
data.
4. On the first server-class send operation issued in the new transaction by the
requester process, the link manager and PATHMON processes provide linkage
with another member of the same server class as the stopped process.
Requester That Has Neither Persistence nor Process Pair
Characteristics
If the requester process is neither persistent, nor runs as a process pair, it can fail if the
requester process calls for an abnormal termination; the processor it is running in fails;
or someone stops the process. Operations protected by transactions are backed out,
but the application becomes unavailable to users of that instance of the requester
because the requester is no longer running.
The requester process must be manually restarted from its beginning for the
application to continue.
Requester Process With Immediate Persistence
A requester process that runs with immediate persistence can still fail, but it will be
immediately, automatically restarted from its beginning. Operations protected by