The catalog address space maintains information about when a catalog, either a BCS or a VVDS, is changed. Each system can identify when a catalog has changed, and a system refreshes its copy of the catalog in main memory only when necessary.

Sharing systems maintain control blocks for each BCS and VVDS accessed. Under normal conditions, these control blocks need no special maintenance.

However, if you cannot access a shared BCS or VVDS after recovery, refresh the control blocks for the BCS or VVDS. Use the MODIFY CATALOG command with CLOSE or UNALLOCATE to remove the control blocks for a BCS. The next request that accesses the BCS rebuilds the control blocks. The control blocks for a VVDS can be removed using the VCLOSE or VUNALLOCATE options of MODIFY CATALOG.

If you recover a shared BCS to a volume with a different volume serial number or device type than the original BCS had, use the access method services IMPORT CONNECT ALIAS command to update the catalog connector record for the BCS in the master catalog of each sharing system.

Sharing catalogs also affects catalog performance. See The Effect of Sharing Catalogs on Cache Usage for more information on the performance of shared catalogs, and Working with the Catalog Address Space for more information on MODIFY CATALOG.