Determining the Number of List Structure Users

Use the MAXCONN parameter to limit the number of users of a list structure. The limit can be one that your application imposes or a limit based on the level of coupling facility that you are using. The limit is returned in the IXLYCONA answer area field CONACFACILITYUSERLIMIT.

When the requested MAXCONN attribute is in the range 0 to 32, the MAXCONN value is 32.

To allocate a structure that can support more than 32 connectors, you must use the MAXCONN keyword on the initial connect request to allocate the structure, and you must ensure that the structure is allocated in a coupling facility of CFLEVEL=17 or higher. Specifying the MAXCONN keyword with any value indicates that the connection can support a user-id limit change that results from a system-managed process (for example, rebuild). XCF communicates the user-id limit change through the structure state change event. Specifying the MAXCONN keyword with a value greater than 32 indicates that the connector can understand events for connections. Events have a target connection (the connector to which the event is being delivered to) and a subject connection (the connector that is the subject of the event) with connection identifiers up to the specified value (for example, EeplExistingConnection or EeplNewConnection).

The total number of list structure users is the minimum of one of the following:

MAXCONN parameter on IXLCONN.
Number of CONNECT records that the CFRM policy accepts. (These records limit the number of connections per structure.)
User-id limit based on the coupling facility level.

For the rebuild of a list structure, you can specify a MAXCONN value that is greater than the number of in-use connections to the old structure instance. If you specify a MAXCONN value that is less than the number of in-use connections to the old structure instance, the request fails with reason code IXLRSNCODEINCOMPATNUMUSER.

Installations should not use more than 32 instances of the application until the following recommendations are met.

You have upgraded all the relevant application instances to a level that supports greater than 32 connectors.
The sysplex contains at least two coupling facilities that are CFLEVEL=17 or higher.

Failure to implement these recommendations can result in an unsafe migration path to greater-than-32 connectors to a structure and can lead to failed connection attempts, failure to rebuild the structure, or failure to duplex the structure.