Overview of Connect Processing

You connect to a coupling facility structure to use XES services to manipulate structure data. The system administrator must define the characteristics of the structure in an administrative CFRM policy and an operator must activate that policy before you can connect to the structure.

The first user to Start of change successfully End of change connect to a structure causes the structure to be allocated in a coupling facility, using the attributes from both the policy definition and the IXLCONN parameters. Subsequent connectors to the structure cannot change these initial attributes, unless all connectors agree to rebuild (ALLOWREBLD=YES) or alter (ALLOWALTER=YES) the structure with new attributes. The number of users that are allowed to connect to a structure is a function of the coupling facility model, the CFRM couple data set format statements, and for a lock structure, a user-supplied limit when the lock structure is allocated.

Start of change If you wish your IXLCONN request to perform only a connection but not an allocation of the structure, consider specifying ALLOC=NO on the request. For example, if you connect to a structure only to work with existing structure data, and the structure was potentially not allocated, then coding ALLOC=NO could avoid the unnecessary allocation of a new structure. End of change

A connector to a structure is aware of other connectors to the same structure, (called peer connections), through its event exit.

Upon successful completion of your IXLCONN request, you

Receive data in the connect answer area (mapped by IXLYCONA)
Are connected to the coupling facility structure you requested
Can request structure services that are valid for this type of structure
Will be notified about other connections to this structure through your event exit. (Any other active connections to the structure also are notified of your connection through their event exits.)

Note: If you are connecting to a lock or a serialized list structure, the system joins an XCF group for your connection. You might need, therefore, to allow for an increase in the number of XCF groups and reformat the sysplex couple data set accordingly. Be aware that this XCF group is strictly for the system's use. If you wish to use XCF services, then you must join your own group using IXCJOIN.

If your IXLCONN request does not complete successfully, you might decide to use the ENF notification of events to determine whether to retry the request. Users waiting to connect to a structure can use ENF event code 35 to be notified when coupling facility resources become available. Whether a subsequent IXLCONN request will be successful depends on the then current set of factors, such as whether the structure dumping or structure rebuild processing is in progress.

For planned reconfiguration or recovery, connected users to a structure can rebuild the structure. The new structure has the same name as the old structure, but can be placed in a different coupling facility and can have some changed attributes, such as size. All connected users must participate in the rebuilding process or else must disconnect from the structure. Rebuilding requires stringent coordination among the participating systems; checkpoints in the form of event notifications require responses from all participants.

For improved availability and usability, connected users to a cache structure can duplex the structure. By default, the new instance of the structure is placed in a different coupling facility and has the same or better connectivity as the old structure. As with rebuilding, all connected users must participate in the user-managed duplexing process, all participating systems are required to coordinate their actions, and all participating systems are required to respond to event notifications.