VSAM Interview Questions (11 - 20)
11. What is the utility program closely associated with VSAM?
The utility program most closely associated with VSAM is IDCAMS (Integrated Data Cluster Access Method Services). IDCAMS is used to define, manage, and manipulate VSAM datasets. It provides commands for tasks such as creating, deleting, and listing datasets.
12. There are at least seven IDCAMS commands; name and explain each of them.
Here are seven commonly used IDCAMS commands:
- ALTER: Modifies attributes of existing VSAM objects like clusters, alternate indexes, or paths.
- BLDINDEX: Builds an alternate index for a VSAM dataset, enabling access through different keys.
- DEFINE: Creates new VSAM datasets, clusters, alternate indexes, or paths.
- DELETE: Removes existing VSAM objects from the catalog.
- LISTCAT: Lists information about VSAM datasets and their attributes.
- PRINT: Prints the contents of a VSAM dataset for review or debugging.
- REPRO: Copies records from one dataset to another, useful for backup or data migration.
13. What are the three levels of definition for the VSAM DEFINE?
When defining a VSAM dataset using the DEFINE command, there are three levels:
- DEFINE CLUSTER: Specifies the overall dataset and its attributes.
- DATA: Defines the data component, detailing how the actual data records are stored.
- INDEX: Defines the index component, which manages the keys and facilitates quick data retrieval.
14. What is the significance of the SHAREOPTIONS parameter?
The SHAREOPTIONS parameter in VSAM defines how a dataset can be shared among multiple users or jobs. It has two sub-parameters:
- Cross Region (first value): Specifies how the dataset can be shared among tasks within the same system.
- Cross System (second value): Specifies how the dataset can be shared among tasks across different systems.
15. What is the meaning of the DEFINE MODEL parameter?
The DEFINE MODEL parameter in VSAM is used to create a new dataset by modeling it after an existing one. This means the new dataset will inherit attributes such as record size, key length, and other properties from the existing dataset, simplifying the creation process.
16. What are the RECOVERY and SPEED parameters in the DEFINE CLUSTER command?
In the DEFINE CLUSTER command:
- RECOVERY: Preformats control areas during the initial dataset load, allowing for job restart if a failure occurs.
- SPEED: Does not preformat control areas, leading to faster initial data loading but without built-in recovery options.
These parameters are mutually exclusive; specifying one excludes the other.
17. Describe the SHAREOPTIONS parameter (SHR) in the DEFINE CLUSTER command.
The SHAREOPTIONS parameter defines how a dataset can be shared across regions and systems:
- Cross-Region (CRvalue): Specifies sharing capabilities within the same system.
- Cross-System (CSvalue): Specifies sharing capabilities across different systems.
Values range from 1 to 4, indicating different levels of read and write access permissions.
18. What does the KEYRANGES parameter in the DEFINE CLUSTER command do?
The KEYRANGES parameter allows you to divide a large dataset into multiple volumes based on specified key ranges. This can enhance performance by enabling concurrent access to different segments of the dataset.
19. How many times is secondary space allocated?
Secondary space allocation can occur up to 122 times. This means that after the primary space is filled, the system can allocate additional extents (secondary space) up to 122 times to accommodate more data.
20. Explain Freespace.
FREESPACE is a parameter in VSAM used to reserve space in data and index components for future insertions.
FREESPACE(20 10)- 20 → % of free space in each data control interval (CI)
- 10 → % of free space in each index control interval