Preventing Lockouts

CATALOG MANAGEMENT uses the SYSIGGV2 reserve while serializing access to catalogs. The SYSIGGV2 reserve is used to serialize the entire catalog BCS component across all I/O as well as to serialize access to specific catalog entries. The SYSZVVDS reserve is used to serialize access to associated VVDS records. The SYSZVVDS reserve along with the SYSIGGV2 reserve provide an essential mechanism to facilitate cross system sharing of catalogs.

Preventing lockouts: When your data sets reside on the same volume as other shared catalogs, deadlocks can occur. An example is shown in Figure 1. In this example, SYS 1 and SYS 2 share DASD volumes, VOLSER1 and VOLSER2. The SYSIGGV2 reserve is held for CATALOG A by SYS 1 while trying to obtain a reserve for data set A. SYS 2 has a SYSIGGV2 reserve for CATALOG B while trying to obtain a reserve for data set B. Reserves for data set A or data set B could be for SYSVTOC or SYSZVVDS. You can prevent such deadlocks, by always converting the SYSIGGV2 reserves to SYSTEMS ENQUEUEs using Global Resource Serialization (GRS) or an equivalent product. The resources SYSZVVDS or SYSVTOC should be either both converted or both excluded in the GRS RNL lists. The important point about SYSZVVDS and SYSVTOC is that they both be treated the same way, either both converted or both excluded. You should review info apar II14297 which contains a number of items to consider when sharing catalogs and the GRS RNL definitions that cover sharing catalogs. For further information concerning catalog serialization, see z/OS MVS Planning: Global Resource Serialization.

Figure 1. Data Sets Residing on the Same Volume as Other Shared Catalogs

Lockouts that occur because of a failure to convert the SYSIGGV2 reserve are not system failures for which the IBM® System Support personnel are able to provide assistance. You prevent these lockouts by ensuring that your support personnel has converted the SYSIGGV2 reserve.

Preventing a lockout due to resource SYSIGGV2 contention: In rare situations, a lockout may occur when a different address space (instead of the Catalog Address Space) obtains the resource SYSIGGV2 exclusive for a catalog as an ECS rebuild for the structure is in progress. Note that it doesn't matter if the catalog is ECS-active or not. Some of the applications that obtain SYSIGGV2 exclusive are DFDSS and IDCAMS IMPORT. IBM recommends that these functions should not run simultaneously on catalogs when ECS is active since a rebuild could occur at any time. However, if contention does occur because of a rebuild, issue the D GRS,RES=(SYSIGGV2,*) command to determine the job and the owner of the resource SYSIGGV2. Proceed to cancel the job and the rebuild should then complete successfully. You can rerun the cancelled job as soon as the rebuild completes.

You can also resolve the problem by deactivating ECS temporarily with command F CATALOG,DISCONNECT on one of the systems in the sysplex. This will cause all systems to quiesce ECS activity. Once the applications are finished running, re-enable ECS by connecting the disconnected system back into ECS (F CATALOG,ECSHR(CONNECT)) and then turn on AutoAdd (F CATALOG,ECSHR(AUTOADD)) to add catalogs back into ECS.

SYSIGGV2 BCS resource is no longer raised for each catalog request to a catalog in RLS mode. Instead, the SMSVSAM address space will obtain data set and record locks from the CF lock structure on a catalog’s behalf.