SNAX/APC Application Programming Manual

Using the Application Program Interface
SNAX/APC Application Programming Manual—138786
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Support of APPC Sync Point Services in SNAX/APC
Support of APPC Sync Point Services in
SNAX/APC
General Description of Sync Point Services
The APPC architecture describes the synchronization point (sync point) services as
follows.
The sync point services allow all Transaction Programs (TPs) processing a distributed
transaction to coordinate error recovery and maintain consistency among distributed
resources such as data bases.
The sync point services affect protected resources. These include conversation resources
and implementation or installation-designated resources such as data bases. Any changes
to a protected resource are logged so that they can be either backed out if the transaction
detects an error, or committed if the transaction is successful.
The TPs divide the distributed transaction into discrete, synchronized Logical Units of
Work (LUWs), delimited by sync points. LUWs are sequences of operations that are
indivisible units for the application. Any failure in the LUW invalidates the entire LUW
and the transaction is backed out to the previous sync point.
Sync point services are carried out with the use of the following components:
•
Sync point Services Component (SPS): This is a component of LU Presentation
Services (PS) also known as sync point manager. It coordinates the sync point
function at each LU. For each TP process participating in the distributed LUW, the
corresponding PS. SPS tracks the state of that LUW by propagating the following
sync point commands throughout the network. These commands are transmitted in
Presentation Services (PS) Headers:
•
PREPARE: Solicits Request Commit or Forget. This command tells the
receiving side to place its protected resources in a state that allows them to be
fully committed to the changes that have been accumulated during this LUW,
but that also allows these changes to be backed out.
•
REQUEST COMMIT: Solicits Committed. This command indicates that the
issuer has succeeded in preparing all of its protected resources.
•
COMMITTED: Confirms Committed. This command informs the soliciting
sync point manager that all resources attached through this conversation are
committed.
•
FORGET: This command informs the Committed sync point manager that its
log record for this LUW can be erased. FORGET also tells the initiating sync
point manager that the sync point is complete and that it can return control to the
TP.
•
BACKED-OUT: This command informs the receiving sync point manager that
the sending sync point manager has backed out the LUW.
•
Conversation-Protected Resource Manager (C-PRM): Each protected resource has a
protection manager that logs significant state changes during an LUW, detects errors