Activating protected conversations
z/OS® uses a construct with z/OS Resource Recovery Services (RRS) called a context.
Definition: A context is the entity for which resource managers perform services, to which they allocate resources and lock ownership, and in which they can express interest in participating in the protocol to ensure that the resource is updated in an orderly manner.
The type of context that the resource manager creates, owns, and manipulates is called the private context. A resource manager can create a context on behalf of another resource manager. RRS uses the private context to identify an application program's unit of work to maintain information for the resource manager concerning which of their resources are associated with the unit of work.
APPC as the communications manager
When
APPC is the communications manager, RRS support
is activated when a conversation is allocated with SYNCLVL=SYNCPT.
This type of conversation is a protected conversation.
When SYNCLVL=SYNCPT is
specified, APPC acquires a private context on behalf of IMS. IMS provides
its resource manager name to APPC in its identity call. APPC provides
the private context to IMS as
the message header. IMS, using
this context, then assumes the role of a participant in the two-phase
commit process with the sync-point manager, RRS.
In
addition to the SYNCLVL=SYNCPT, the keyword ATNLOSS=ALL must
be specified in the VTAM definition file for whichever LUS need
to be enabled for protected conversations.
Using OTMA with protected conversations
In an OTMA environment, OTMA is not a resource manager registered with RRS. The process remains an inter-process protocol between a server (IMS) and a number of clients (application programs). Therefore, OTMA cannot obtain a private context token to pass to IMS, as APPC does. The client-adapter code that uses OTMA is responsible for obtaining and owning a private context, and for providing the context ID. In messages passed between the partners, the context-ID field contains the context token (if it is a protected conversation).
When IMS finds the context-ID in the message, IMS assumes the role of a participant in the two-phase commit process, as it does in the APPC environment.
XRF and protected conversations
Running protected conversations (using RRS with either APPC/PC or OTMA) in an IMS-XRF environment does not guarantee that the alternate system can resume and resolve any unfinished work started by the active system. A failed resource manager must re-register with its original RRS system if the RRS system is still available when the resource manager restarts. Only if the RRS on the active system is not available can an XRF alternate system register with another RRS in the sysplex and obtain the incomplete unit of recovery data of the failing active system.