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Structure allocation when rebuilding a structure z/OS MVS Setting Up a Sysplex SA23-1399-00 |
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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:
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:
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. |
Copyright IBM Corporation 1990, 2014
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