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 −
Entry sequenced datasets (ESDS), Key sequenced datasets (KSDS), Relative record dataset (RRDS) and Linear dataset (LDS).
A control interval is the unit of information that VSAM transfers between virtual and auxiliary storage.
Records are stored in the order in which they are included in the file.
A group of control intervals makes up a control area.
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.
The catalog contains the names of all datasets, VSAM and non-VSAM. It is used to access these datasets.
An alternate index is a file that allows access to a VSAM dataset by a key other than the primary one.
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.
Free space is reserved within the data component of a KSDS to accommodate insertion of new records.
Primary key values must be unique and alternate key values need not be unique.
The ORGANIZATION for KSDS is INDEXED.
ACCESS can be SEQUENTIAL, RANDOM or DYNAMIC.
File Status provide information about each I/O operation for the file.
IDCAMS the access method services utility is associated with VSAM.
They are DEFINE CLUSTER, DATA and INDEX.
Run VERIFY.
'02' indicates Non-Unique Alternate Index duplicate key found.
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.
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.
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.
First step is Define Alternate Index. Second is Define Path and third step is Building Index.
ALTER command is used to change most of the VSAM dataset attributes that were specified while defining VSAM cluster.
