TOP VSAM Interview Questions and Answers
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?
Sequential (QSAM) files can be created on tape while ESDS files cannot. Also, you can have ALTINDEX for an ESDS while no such facility exists for QSAM files.
How do you calculate record size of an alternate cluster? Give your values for both unique and nonunique?
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.
Do all versions of the GDG have to be of the same record length?
No, the DCB of the model dataset can be overridden when you allocate new versions.
Suppose 3 generations of a GDG exist. How would you reference the 1st generation in the JCL?
Use GDG name(-2).
What more info you should give in the DD statement while defining the next generation of a GDG?
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?
They are DEFINE CLUSTER, DATA and INDEX.
What is the utility program closely associated with VSAM?
IDCAMS, the access method services utility.
What is the VSAM-code field?
It is a COBOL II enchancement to VSAM batch processing expanding the FILE STATUS field. It is defined in WORKING-STORAGE as a six byte group item with three two byte elements, the normal return code, the function code and the feedback code.
What is the meaning of dynamic processing?
It’s rarely used. It means one program uses both sequential and random processing for a VSAM KSDS file.
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?
The maximum condition code generated is returned as the condition code of the IDCAMS step.
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.
What is the meaning of each of the values in SHAREOPTS (2 3)?
Value of 2 for cross region means that the file can be processed simultaneously by multiple users provided only one of them is an updater. Value of 3 for cross system means that any number of jobs can process the file for input or output (VSAM does nothing to ensure integrity).
How do you define an ALTINDX? How do you use ALTINDXs in batch, CICS programs?
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?
They are end of file (10), duplicate key (22), record not found (23), VSAM logic error (90), open problem (92) and space problem (93).
What is a VSAM slot?
A relative record dataset (RRDS) consists of a specified number of areas called slots. Each slot is identified by a relative record number (RRN) which indicates its relative position in the file.
There are at least seven IDCAMS commands name and explain each of them?
ALTER modifies information for a catalog, alternate index, cluster or path. BLDINDEX builds the alternate index, of course. DEFINE is used for ALTERNATEINDEX, CLUSTER or PATH. DELETE removes the catalog entry for a catalog, cluster, alternate index or path. LISTCAT lists information about the dataset. PRINT prints the dataset contents. REPRO copies records from one file to another.
What is the significance of the SHAREOPTIONS parameter?
It specifies how the file may be shared between jobs and between batch and CICS environments.