Most Asked VSAM Interview Questions and Answers
What is File Status in VSAM?
The File STATUS clause of the FILE-CONTROL paragraph allows for each file to be associated with a file status key (i.e., the 2-character data item specified in the FILE STATUS clause). If the FILE STATUS clause is specified for a given file, a value indicating the status of each I/O operation against that file is placed in the associated file status key. This value is stored in the file status key as soon as the I/O operation is completed (and before execution of any EXCEPTION/ERROR declarative or INVALIDKEY/AT END phrase associated with the I/O request).
Note: This element may behave differently when the CMPR2 compiler option is used. The file status key is divided into two status keys: the first character is known as file status key1; the second character is file status key 2.
If you wish to use the REWRITE command haw must the VSAM file be opened?
It must be opened as I/O.
What is the COBOL RECORD KEY clause?
The RECOED KEY in the SELECT clause identifies the files primary key as it will be known to the program.
In the COBOL SELECT statement what is the ORGANIZATION for a KSDS?
The ORGANIZATION is INDEXED.
What is the base cluster?
The base cluster consists of the data component and the index component for the primary index of a KSDS.
What is free space?
Free space is reserved within the data component of a KSDS to accommodate inserting new records.
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 a CI, control interval?
A control interval is the unit of information that VSAM transfers between virtual and auxilliary storage.
What is a CA, control area?
A group of control intervals makes up a control area.
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 the catalog?
The catalog contains the name of all datasets. VSAM and non-VSAM. It is used to access these datasets.
What is the purpose of the FILE STATUS clause in the SELECT statement?
The FILE STATUS field identifies the field that VSAM uses to provide information about each I/O operation for the file.
In the COBOL SELECT statement for a KSDS what are the three possibilities for ACCESS?
ACCESS can be SEQUENTIAL, RANDOM or DYNAMIC.
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.
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 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 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 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 a sequence set?
This is the part of the index that points to the CA and CI of the record being accessed.
What are the distinctive features of a KSDA, key sequenced dataset?
The index and the distributed free space.
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 are the types of VSAM datasets?
Entry sequenced dataset (ESDS), key sequenced datasets (KSDS) and relative record dataset (RRDS).