Determining the Number of Lock Structure Users

Use the NUMUSERS or MAXCONN parameters to limit the number of users of a lock structure. The limit can be one that your application imposes or may be a limit based on the level of coupling facility you are using. The limit is returned in the IXLYCONA answer area, field CONAFACILITYMAXLOCKUSERS.

When the NUMUSERS keyword is used by any connection to the structure, the actual number of connections that is supported by the structure does not exceed 32. This rule also applies when the IXLCONN is issued for the rebuild process. To allocate a structure that supports more than 32 connectors, you must use the MAXCONN keyword on the initial connect request to allocate the structure, you must ensure that the structure is allocated in a coupling facility of CFLEVEL=17 or higher, and all subsequent IXLCONN requests must specify the MAXCONN keyword with a value greater than 32. 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 subject connections with connection identifiers up to the specified value specified (for example, EeplExistingConnection or EeplNewConnection).

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

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

The number of lock structure users is returned in field CONALOCKNUMUSERS in IXLYCONA.

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

If you do not specify the same keyword (either MAXCONN or NUMUSERS) on the initial connect request and the rebuild connect request, the rebuild connect request fails with reason code IXLRSNCODEBADLOCKNUMUSER.

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.