The structure alter function allows a coupling facility structure to be reconfigured with minimal disruption to connectors. Structure alter provides for the expansion or contraction of the size of a structure, the reapportionment of the entry-to-element ratio of the structure's storage, and the alteration of the percentage of structure storage set aside for event monitor controls (EMCs). The structure being altered is not deallocated and then re-allocated; it is altered in place.

All functions of structure alter can be initiated by an authorized program; structure size only can be initiated by an operator command. Both methods are supported on an SP 5.2 and higher system. It is highly recommended that applications support the structure alter protocol, especially those applications whose only rebuild method supported is system-managed (IXLCONN ALLOWREBLD=NO,ALLOWAUTO=YES).