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VSAM Interview Questions
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List of VSAM Interview Questions and Answers PDF

What is VSAM?

VSAM stands for Virtual Storage Access Method. It’s a Data Management method used to organize, store, catalog, retrieve and delete the datasets in mainframe system (VSAM and Non-VSAM). This access method makes it easier for an application to execute an I/O operation (moving data between an I/O device and memory). In fact VSAM is the first access method designed for Virtual Storage Environment.

VSAM supports fixed as well as variable length records. These records are placed in blocks of Control Intervals and these control intervals are further placed as Control Area (CA consists of multiple CIs).

What are the advantages of VSAM?

Accessing the data is faster and easier.
VSAM supports more dataset types.
Supports variety of I/O Techniques.
Improves Efficiency.
Records can be accessed sequentially or randomly.

What are the disadvantages of VSAM?

VSAM Datasets require more storage space compared to other type of datasets due to Control information(CI) present in them.
VSAM can’t be stored in TAPE Volume i.e., VSAM Stored only in DASD.
VSAM is not a database like DB2, IMS DB & IDMS.

What are the different types of VSAM files available?

ESDS: Entry Sequence Data Set
KSDS: Key Sequence Data Set
RRDS: Relative Data Set

What is purpose of VSAM?

VSAM acts as an interface between Application program & Operating System.

What is the maximum record length for the VSAM dataset?

Max size of a record in VSAM is cylinder = 2880 bytes approx.

What is an alternate index and path?


Is a delete operation possible in an ESDS? B, is rewrite operation possible in ESDS?

No delete operation is not possible in VSAM ESDS.B. yes rewrite operation is possible in an ESDS.

What is the difference between LDS and ESDS?


How to delete a member using JCL?

Using IDCAMS a member can be deleted. DELETE ‘XXX.YYY (memeber)

What is IDCAMS? and what is the purpose of it?

IDCAMS is an access method services utility used for creating, deleting, altering VSAM files and coping sequential file to a VSAM file, etc.


1) FROMADDRESS(address)
2) TOADDRESS(address) where ‘address’ specifies the RBA value of the key of the input record.
4)TONUMBER (rrn) where ‘rrn’ specifies the relative record number of the RRDS record
5) FROMKEY (key)
6) TOKEY (key) where ‘key’ specifies the key of the input record
7) SKIP (number)
8) COUNT (number) where ‘number’ specifies the number of records to skip or copy Ex: REPRO INFILE(DD1) OUTFILE(DD2) SKIP(9000) COUNT(700)-Skips the first 9000 records and begin copying at 9001 and copies 700 records from DD1 to DD2.

What does the KEYRANGES parameter in Define Cluster commends do?

It divides a large dataset into several volumes according to the Key ranges specified. e.g. KEYRANGES ((0000001 2999999) (3000000 5999999)). if the activity on the key ranges are evenly distributed, concurrent access is possible, which is a performance improvement.

Describe SHAREOPTIONS parameter (SHR) in Define Cluster command?


What is RECOVERY and SPEED parameters in DEFINE CLUSTER command?

RECOVERY (default ) and SPEED are mutually exclusive. Recovery pre-formats the control areas during the initial dataset load, if the job fails, you can restart but you must have a recovery routine already written to restart the job. SPEED does not pre-format the CAs. It is recommended that you specify SPEED to speed up your initial data load.



How many Alternate Indexes you can have on a dataset?

255 – but you must be a nut to have so many ALT Indexes on a dataset!

On which dataset You can have ALT INDEX?

Only on KSDS and ESDS – not RROS

What is the meaning of VSAM RETURN-CODE 28?

Out of space condition is raised.


Define new VSAM dataset allocated with more space.
Use IDCAMS to ALTER / rename the old VSAM dataset or se IDCAMS to DELETE the old VSAM datset.

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




How are different versions of GDG named?

base-file-name. GnnnnnnV00 where nnnn=generation number (upto 255). nnnn will be 0000 for the 1st generation.

How do you define a GDG?

Use the DEFINE GENERATIONDATAGROUP command. In the same IDCAMS step, another dataset must be defined whose DCB parameters are used when new generations of the GDG are created. This dataset is known as the model dataset. The DS name of this model dataset must be the same as that of the GDG, so use a disp of keep rather than catlg and also specify space = (trk,0)

What is the difference between sequential files and ESDS files?



UniqueCase: 5 + (alt-key-length + primary – key )

Non unique Case: 5 + (alt-key-length + n * primary – key ) where n = number of duplicate records for the alternate key

How do you load a VSAM data set with records?

Using the REPRO command.




Use GDG name(-2).


Give (+1) as the generation number, give (new, catlg) for disp, give space parameter, can give the DCB parameter if you want to override the DCB of the model dataset.

Assuming that the DEFINE JCL is not available, how do you get info about a VSAM files organisation?

Use the LISTCAT command.

Using Alternate Indexes in CICS program?

FCT entries must be created for both base cluster and the path. To read using the alternate index, use the DD name of the path in CICS file control commands.

Using Alternate Indexes in Batch program?

In the JCL, you must have DD statements for the cluster and for the path9s). In the COBOL program, SELECT … ASSIGN TO ddname for base cluster RECORD KEY IS… ALTERNATE RECORD KEY IS …

What is a LDS (Linear Data Set) and what is it used for?

LDS is a VSAM dataset in name only. It has unstructured 4k (4096 bytes ) fixed size CT’s which do not contain control fields and therefore from VSAM’s standpoint they do not contain any logical records. There is no free space, and no access from Cobol. Can be accessed by DB2 and IMS fast path datasets. LDS is essentially a table of data maintained on disk. The ‘table entries’ must be created via a user program and can only be logically accessed via a user program. When passed, the entire LDS must be mapped into storage, and then data is accessed via base and displacement type processing.

What is the meaning of the DEFINE MODEL parameter?

It specifies whether Daniela Pestova or Yamila – oops! Wrong models! The MODEL parameter allows you to model your cluster by modeling it after an existing cluster.

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


What is the utility program closely associated with VSAM?

IDCAMS, the access method services utility.

What is the VSAM-code field?


What is the meaning of dynamic processing?


Under IDCAMS, multiple functions can be executed, each of which returns a condition code. What will be the condition code returned to the operating system?


Would you specify FREESPACE CE for an ESDS?

No. Because you cannot insert records in an ESDS, also when you rewrite a record, it must be of the same length. Thus putting any value for FREESPACE does not make any sense.




DEFINE ALTERNATEINDEX. Important parameters are RELATE where you specify the base cluster name, KEYS, RECORDSIZE, SHAREOPTION, UNIQUEKEY (or NONUNIQUEKEY), DATA (DS NAME for the data component), INDEX(DS name for the index component). Then DEFINE PATH. Important parameters are NAME (DS name for the path). PATHENTRY (DS name of the alternate index name). UPDATE (or NOUPDATE) which specifies whether an ALT index is updated when a update to the vase cluster takes place. Then BLDINDEX. Paramters are INDATASET (DS name of base cluster), OUTDATASET (DS name of AIX).

Name some common VSAM error conditions and codes?


What is a VSAM slot?


There are at least seven IDCAMS commands name and explain each of them?


What is the significance of the SHAREOPTIONS parameter?


What is File Status in VSAM?


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.


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.



What is the base cluster?


What is free space?


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?


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 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?


What is an alternate index?


What is a cluster?


What is a sequence set?


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?


What are the types of VSAM datasets?

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