ABCs of z/OS System Programming Volume 3 - IBM Redbooks

6.24 Enhanced catalog sharing
MVS 1
VVR
Coupling
Facility
MVS 2
VVR
Figure 6-38 DFSMS enhanced catalog sharing
CATALOG
Conditions for ECS:
ECSHARING in IDCAMS DEFINE/ALTER
Active connection to ECS CF structure
Activate ECS through MVS command:
MODIFY CATALOG,ECSHR(AUTOADD)
Enhanced catalog sharing (ECS)
In 6.9, “Sharing catalogs across systems” on page 343, sharing catalogs across multiple
systems is discussed. A catalog uses its specific VVR to serialize the access from multiple
systems. Reading serialization information from the VVR on the DASD causes a significant
amount of overhead for I/O operations. However, it is better to have this VVR than to discard
the catalog buffers, when in shared catalog mode. This is called VVDS mode.
Most of the overhead associated with shared catalog is eliminated if you use enhanced
catalog sharing (ECS). ECS uses a cache Coupling Facility structure to keep the special
VVR. In addition, the Coupling Facility structure (as defined in CFRM) keeps a copy of
updated records. There is no I/O necessary to read the catalog VVR to verify the updates. In
addition, the eventual modifications are also kept in the Coupling Facility structure, thereby
avoiding more I/O. ECS saves about 50% in elapsed time and provides an enormous
reduction in ENQ/Reserves.
Implementing enhanced catalog sharing
Perform these steps to implement ECS:
1. Define a Coupling Facility cache structure with the name SYSIGGCAS_ECS in the CFRM
couple data set and activate this CFRM policy.
This action connects all ECS-eligible systems to the ECS structure.
Chapter 6. Catalogs 375