In this topic, we have explained about the below sections -
Catalog structure has the below components -
- Data Space
- Unique Clusters
- Non-VSAM Datasets
Below diagram shows the catalog structure and its components.
Catalog maintains the dataset information like data and volumes where it stores and uses the same information while retrieving the information from the dataset. The catalog contains many other characteristics of the dataset, along with unit and volume. Data sets can be cataloged, uncataloged, or recataloged.
All system-managed DASD data sets are cataloged automatically in a catalog.
VSAM dataset information stores in the catalog by default because it stores on DASD, and it is not optional for VSAM datasets. Whereas non-VSAM dataset information does not.
However, the user has an option, DISP=(, CATLG) JCL entry creates the catalog entry for the non-VSAM dataset.
All data sets can be cataloged in a catalog. Catalogs divided into two types, and those are -
- Master Catalog
- User Catalogs
Master Catalog -
Every mainframe system that uses VSAM has only one master catalog. The master catalog contains the information(entries) about both system datasets and VSAM datasets information(structure).
A VSAM or non-VAM datasets can catalog in the master catalog very rarely. Most of the well-managed systems will not allow this cataloging. The system programmers create user catalogs under the master catalog— all users except system programmers are allowed to use their user catalogs to store the VSAM information.
The master catalog was created during the system creation process and usually stores on system residence volume. The master catalog "owns" all other VSAM resource information that is on the system. Because of this, the master catalog was called "VSAM King" in the 1970s.
For example -
In the above example, CATALOG.Z113.MASTER is a catalog and storing in a catalog CATALOG.Z113.MASTER. So it is Master Catalog.
User Catalog -
The user catalog contains the application-specific datasets information (entries). A user catalogs defining information stores in the master catalog. Production system might have many user catalogs based on the application type.
For example -
Let us assume if CATALOG.Z113.USERCTLG is a catalog and storing in CATALOG.Z113.MASTER, then CATALOG.Z113.USERCTLG is user catalog.
VSAM Data Space -
The relationship between the data space and catalog gets established when the VSAM data set is defined on volume. The catalog owns the data space once it links to VSAM dataset. Other data spaces on the same or different volumes can define in the same catalog. i.e., a catalog can have multiple data spaces that are on the same or different volumes.
The catalog describes the information about where and how much data space available and other values. VSAM automatically updates the data space information in the catalog once data space is allocated to a file.
Whenever data space is allocated to a file, VSE/VSAM automatically updates the data space information in the catalog.
Unique Clusters -
A cluster is an association of the index, sequence set, and data portions of the dataset. Every VSAM file type(ESDS, KSDS, RRDS, LDS) has a cluster (base) component and a data component. The cluster name must be different from the data component.
For example -
MATEGJ.TEST.VSAM - Cluster Component MATEGJ.TEST.VSAM.DATA - Data Component
For KSDS or variable-length RRDS, the cluster component has the index component along with the data component.
For example -
MATEGJ.TEST.VSAM - Cluster Component MATEGJ.TEST.VSAM.DATA - Data Component MATEGJ.TEST.VSAM.INDEX - Index Component
- Data Component - Data records are present in the data component of a VSAM cluster.
- Index Component - Index records are present in the index component of a VSAM key-sequenced cluster.
Non-VSAM Datasets -
Non-VSAM datasets (stores on both tape and direct access storage) may have entries in both the master catalog and user catalogs. The non-VSAM dataset may have less information stored than the information stored for a VSAM object.