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v Notification that the resource is not available, requiring temporary suspension
(shunting) of the UOW
v Notification that the resource is available, enabling retry of shunted UOWs
v Notification that a connection is reestablished, and can deliver a commit or
rollback (backout) decision
v Syncpoint rollback
v Normal termination of the UOW
The identity of a UOW and its state are owned by the CICS recovery manager, and
are recorded in storage and on the system log. The system log records are used by
the CICS recovery manager during emergency restart to reconstruct the state of the
UOWs in progress at the time of the earlier system failure.
The execution of a UOW can be distributed over more than one CICS system in a
network of communicating systems.
The CICS recovery manager supports SPI commands that provide information
about UOWs.
Coordinating updates to local resources
The recoverable local resources managed by a CICS region are files, temporary
storage, and transient data, plus resource definitions for terminals, typeterms,
connections, and sessions.
Each local resource manager can write UOW-related log records to the local system
log, which the CICS recovery manager may subsequently be required to re-present
to the resource manager during recovery from failure.
To enable the CICS recovery manager to deliver log records to each resource
manager as required, the CICS recovery manager adds additional information
when the log records are created. Therefore, all logging by resource managers to
the system log is performed through the CICS recovery manager.
During syncpoint processing, the CICS recovery manager invokes each local
resource manager that has updated recoverable resources within the UOW. The
local resource managers then perform the required action. This provides the means
of coordinating the actions performed by individual resource managers.
If the commit or backout of a file resource fails (for example, because of an I/O
error or the inability of a resource manager to free a lock), the CICS recovery
manager takes appropriate action with regard to the failed resource:
v If the failure occurs during commit processing, the UOW is marked as
commit-failed and is shunted awaiting resolution of whatever caused the
commit failure.
v If the failure occurs during backout processing, the UOW is marked as
backout-failed, and is shunted awaiting resolution of whatever caused the
backout to fail.
Note that a commit failure can occur during the commit phase of a completed
UOW, or the commit phase that takes place after successfully completing backout.
(These two phases (or ‘directions’) of commit processing—commit after normal
completion and commit after backout—are sometimes referred to as ‘forward
commit’ and ‘backward commit’ respectively.) Note also that a UOW can be
backout-failed with respect to some resources and commit-failed with respect to
Chapter 2. Resource recovery in CICS 19