Mainframe / VSAM Interview Questions

Mainframe Interview Questions

Cobol | DB2 | JCL | JCL2 | VSAM | VSAM2

What are the types of VSAM dataset?

. Entry sequenced dataset (ESDS), key sequenced dataset (KSDS) and relative record dataset (RRDS).

How are records stored in an ESDS, entry sequenced dataset?

They are stored without respect to the contents of the records and in the order in which they are included in the file.

What is a CI, control interval?

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

. What are the distinctive features of a ksds, key sequenced dataset?

The index and the distributed free space

What is a CA, control area?

A group of control intervals makes up a control area.

What is a sequence set?

This is the part of the index that points to the CA and CI of the record being accessed.

What is the index set?

This is the other part of the index. It has multiple levels with pointers that ultimately reach to the sequence set.

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, ie. to all parts of the dataset simultaneously.

What is the catalog?

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

What is an alternate index?

An AIX 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 the upgrade set?

The upgrade set is the list of all AIXes that VSAM must maintain for a specific base cluster, so that when data in the base cluster is updated, the AIX files are also updated.

What is free space?

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

What is a VSAM split?

If there isn't enough space in the control interval VSAM performs a control interval split by moving some records to the free control intervals. If there isn't a free control interval VSAM performs a control area split by allocating a new control area and moving half of the control intervals to it.

What is the base cluster?

The base cluster consists of the data component and the index component for the primary index of a KSDS.

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

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

In the COBOL SELECT statement what is the ORGANIZATION for a KSDS?

The ORGANIZATION is INDEXED.

In the COBOL SELECT statement for a KSDS what are the three possibilities for ACCESS?

ACCESS can be SEQUENTIAL, RANDOM or DYNAMIC.

Mainframe / DB2 Interview Questions