Structure allocation when rebuilding a structure

The results of structure allocation during the rebuild process, whether user-managed or system-managed, may differ significantly from those during initial allocation, depending on what system conditions exist. The size of a structure undergoing a rebuild or duplexing rebuild process might require more coupling facility storage than specified by the SIZE parameter in order to allocate the new structure. As a general rule, SIZE specifies the maximum size to which a structure can expand. However, because the rebuild process requires that the rebuilt structure contain the objects from the original structure, and because storage algorithms for different coupling facilities may yield different results, the coupling facility configuration may dictate that additional storage is needed to accomodate the allocation of the new structure. For example, a coupling facility at CFLEVEL=15 would require more storage for a list structure than a coupling facility at CFLEVEL=14 would for the same structure. Conversely, for rebuild purposes, a structure might be allocated with a size smaller that INITSIZE or the value specified or defaulted to for MINSIZE.

When a user-managed rebuild or duplexing rebuild process is initiated, the system determines whether either of the following conditions exist:

The installation has changed the SIZE specification in the CFRM policy, and the policy change is pending.
The application has changed any structure attributes on its IXLCONN REBUILD request. (The application may initiate a structure rebuild for the purpose of modifying the structure attributes.)

If either of these conditions is true, the system attempts to allocate the new structure as previously described for initial allocation. If you are migrating to a new coupling facility or a new operating system level when either of these conditions is true, your policy SIZE and/or INITSIZE values must accomodate the required control space; otherwise, the rebuild will fail.

On the other hand, if neither of these conditions exist, or the rebuild process is system-managed, the system allocates the new structure based on the attributes of the initial structure. The system will allocate the structure large enough to contain all the objects that had been allocated in the old structure. The allocated size of the new structure:

Might be larger than the maximum size indicated by SIZE.
Might be between the INITSIZE and SIZE values. (Perhaps in order to be able to copy all data that must be copied from the old structure to the new structure.)
Might be less than INITSIZE. (Perhaps because of a coupling facility storage constraint, but the small size still provided a sufficient number of structure objects to allow the copy process to succeed.)
Might be less than MINSIZE. (Perhaps because of a coupling facility storage constraint, as long as there is enough space in the new structure to copy all the inuse objects from the old structure.)

After the rebuild process is complete, the installation should display the actual amount of storage allocated to the structure by issuing the DISPLAY XCF,STRUCTURE command. It might then be necessary to update the CFRM policy with appropriate size values so that future initial allocations will not fail. Such failures could occur because during initial structure allocation, the system does not allow the size of a structure to exceed the SIZE specified in the active CFRM policy.