VSAM - Interview Questions

Dear readers, these VSAM Interview Questions have been designed especially to get you acquainted with the nature of questions you may encounter during your interview for the subject of VSAM File System. As per my experience, good interviewers hardly planned to ask any particular question during your interview, normally questions start with some basic concept of the subject and later they continue based on further discussion and what you answer −

What are the different types of VSAM datasets?

Entry sequenced datasets (ESDS), Key sequenced datasets (KSDS), Relative record dataset (RRDS) and Linear dataset (LDS).

What is a control interval?

A control interval is the unit of information that VSAM transfers between virtual and auxiliary storage.

How are records stored in an ESDS?

Records are stored in the order in which they are included in the file.

What is a control area?

A group of control intervals makes up a control area.

What is a cluster?

A cluster is the combination of the index, sequence set and data portions of the dataset. The operating system gives program access to the cluster, that is to all parts of the dataset simultaneously.

What is the catalog?

The catalog contains the names of all datasets, VSAM and non-VSAM. It is used to access these datasets.

What is an alternate index?

An alternate index is a file that allows access to a VSAM dataset by a key other than the primary one.

What is a path?

A path is a file that allows you to access a file by alternate index. The path provides an association between the AIX and the base cluster.

What is free space?

Free space is reserved within the data component of a KSDS to accommodate insertion of new records.

Do primary key values and alternate key values have to be unique?

Primary key values must be unique and alternate key values need not be unique.

What is the ORGANIZATION for a KSDS in COBOL SELECT statement?

The ORGANIZATION for KSDS is INDEXED.

What are access modes available for KSDS dataset?

ACCESS can be SEQUENTIAL, RANDOM or DYNAMIC.

What is the purpose of the FILE STATUS clause in the SELECT statement?

File Status provide information about each I/O operation for the file.

What is the utility program closely associated with VSAM?

IDCAMS the access method services utility is associated with VSAM.

What are the three levels of definition for the VSAM DEFINE?

They are DEFINE CLUSTER, DATA and INDEX.

During processing of a VSAM file, some system error occurs and it is subsequently unusable . What do you do?

Run VERIFY.

What does '02' file status code indicate?

'02' indicates Non-Unique Alternate Index duplicate key found.

What are Unique Cluster?

Unique Clusters consists of a separate data space which is utilized completely by the cluster created within it. Unique clusters are created out of unallocated space on direct access storage.

What are Sub-allocated Clusters?

A sub-allocated VSAM file shares the VSAM space with other sub-allocated files. It specifies that file should be sub-allocated within existing VSAM space. Sub-allocation is used for easier management and control of VSAM spaces.

What is Upgrade and Noupgrade option in Alternate Index?

UPGRADE specifies that the alternate index should be modified if the base cluster is modified and NOUPGRADE specifies that the alternate indexes should be left alone if the base cluster is modified.

Explain different steps to create Alternate Index?

First step is Define Alternate Index. Second is Define Path and third step is Building Index.

What is the use of ALTER command in VSAM?

ALTER command is used to change most of the VSAM dataset attributes that were specified while defining VSAM cluster.