Understanding the Structure Version Numbers

The structure version number (CONAPHYSICALSTRUCTUREVERSION) is used to identify the instance of a structure with a given name. The structure version number changes when a new instance of the structure is allocated, as in a user-managed or system-managed rebuild, when there is at least one active connector to observe the allocation. For example, in a user-managed rebuild, the value of the physical structure version number that is returned on an initial connect to a structure might be “A”. When the IXLCONN REBUILDs are performed during the user-managed rebuild process, the physical structure version number returned for the new structure might be “B”. Keeping track of a structure's physical structure version number allows you to uniquely identify the instance of the structure with which you are working.

In OS/390® Release 8, a second physical structure version number (CONAPHYSICALSTRUCTUREVERSION2) is introduced. This version number is used only in system-managed protocols. Its purpose, in combination with CONAPHYSICALSTRUCTUREVERSION, is to uniquely identify an instance of a structure. For example, if a connector supports system-managed protocols (that is, specifies ALLOWAUTO=YES), the version numbers received on initial connect might be:

CONAPHYSICALSTRUCTUREVERSION: A
CONAPHYSICALSTRUCTUREVERSION2: 0

During a system-managed rebuild, the version numbers provided with the Structure State Change event might be:

EEPLSSCSTRPHYSICALVERSION: B
EEPLSSCSTRPHYSICALVERSION2: 0

During a system-managed duplexing rebuild, it is likely that both version numbers will contain non-zero values.

Because the two pairs of values are not identical, the connector can recognize that a new instance of the structure has been allocated. The following describes how these fields are intended to be used.

When presented to the connector, whether via the Structure State Change Notification event or as the result of a connect request, the connector should “harden” both physical structure version numbers on whatever external media are used for recording such persistent information about structures in use.
On any subsequent connect to the structure, the connector should compare both returned physical structure version numbers against both of the saved physical structure version numbers. If either nonzero structure version number returned on the connect request matches either of the two nonzero saved physical structure version numbers, then the user is connected to a viable structure instance and no special structure data recovery processing is required. Otherwise, such data recovery is required.