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VSAM Interview Questions & Answers - Learning Mode

VSAM Interview Questions & Answers - Learning Mode

VSAM stands for Virtual Storage Access Method. VSAM is a file storage access method used in MVS, ZOS and OS/390 operating systems. It was introduced by IBM in 1970's. It is a high performance access method used to organize data in form of files in Mainframes. Virtual storage access method (VSAM) is an IBM DASD file storage access method, first used in the OS/VS1, OS/VS2 Release 1 (SVS) and Release 2 (MVS) operating systems, later used throughout the Multiple Virtual Storage (MVS) architecture and now in z/OS.

Try VSAM Interview Questions & Answers - Exam Mode

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VSAM Interview Questions & Answers - Learning Mode
Try VSAM Interview Questions & Answers - Exam Mode
Question: How do you compile a program in Endevor?

Answer: To compile a program through Endeavor.

We need tp prepare aan ADDSCL to compile a program through Endeavor.The following points to be noted while preparing ADDSCL.

1.In which environment are we going to add a program.?As you all know there are different environments in Endeavor such as Production, Test, Accpetance, QuickFix Etc., and it is installation dependent.

2.Select the environment, say if you are adding a program in Test environment

3.Goto Test environment => Source:
Question: What is the difference between sequential files and ESDS files?

Answer: 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. Source:
Question: How can we read a KSDS file in a COBOL program in reverse order,that is from last record to the first record in KSDS file? Provided the keys are in unsorted order. And this has to be done without sorting the KSDS file. Could any one please help me for this?

Answer: Firstly, The Keys are in sorted order in KSDS .
Secondly , to acheive reverse reading
- Use StartBrowse to point it to last record with by moving Keys to HIGH values .
-Then use READPREV to read records ...
Question: What do you mean by RDW in VSAM?

Answer: VSAM Stands for Virtual Storage Acess Method...An Acess method is the component of operating is the interface between Application Program and the physical opertaion of storage device.What is a VSAM? VSAM Stands for Virtual Storage Acess Method...An Acess method is the component of operating is the interface between Application Program and the physical opertaion of storage device.[B][/B] Source:
Question: What do you mean by dirty read

Answer: The "dirty read" technique can be used to provide a high degree of concurrent access to VSAM files while avoiding the complications associated with CI and CA splits. The dirty read protocol can be summarized as follows:
The VSAM file must be defined with cross-region SHAREOPTIONS 4.
The file must be allocated with DISP=SHR.
All operations on the file, including reads, must be preceded with an ENQ for the data set. The data set name is specified for the ENQ "rname", but any string can Source:
Question: How do you define an ALTINDX ? How do you use ALTINDXs in batch, CICS pgms ?

Answer: DEFINE ALTERNATEINDEX. Important paramters are RELATE where you specify the base cluster name, KEYS, RECORDSIZE,SHAREOPTIONS,UNIQUEKEY(or NONUNIQUEKEY), DATA(ds name for the data component), INDEX(ds name for the index component).

Then DEFINE PATH. Important paramters 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 base cluster takes place.

Then BLDINDEX. Param Source:
Question: How do you define a GDG ?

Answer: 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) Source:
Question: What is the maximum record length for the VSAM dataset?

Answer: Max size of a record in VSAM is cylinder = 2880 bytes approx.
Question: How do you load a VSAM data set with records ?

Answer: Using the REPRO command. Source:
Question: Would you specify FREESPACE for an ESDS?

Answer: 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. Source:
Question: What does a file status of 02 on a VSAM indicate?

Answer: Duplicate alternate key . Happens on both input and output operation Source:
Question: What is the maximum no. of records that can be allowed in VSAM

Answer: Its depand upon the CA. Every vsam file allocate record differently. so, its tuff to tell the answer. Source:
Question: Suppose a generation of GDG gets created in a particular step of a proc. How would you refer the current generation in a subsequent step? What would be the disposition of this generation now?

Answer: Relative generation numbers are updated only at the end of the job, not at the end of a step. To allocate a new generation, we would be using (+1) with a DISP of (NEW,CATLG,DELETE). To refer to this in a subsequent step in the same job, we would again use (+1) but with a DISP of SHR or OLD. Source:
Question: How do you decide on optimum values for CI, FREESPACE etc..?

Answer: CI size should be based on record length, type of processing. Usually CI is 4K. If record length is larger(>1K), chose 6K or 8K.

FREESPACE should be large if more number of insertions are envisaged. Usual values are (20 20) when heavy updates are expected. CI size can be calculated. Source:
Question: Assuming that the DEFINE jcl is not available, how do you get info about a VSAM file?s organisation ?

Answer: Use the LISTCAT command. Source:
Question: What is averange record legth in KSDS?

Answer: The average record length must be less than or equal to the maximum record length. The Maximum Record Length is 2046. Source:
Question: In vsam why we use export-import utility?

Answer: It is used for the back-up purpose.Whenever there is a loss of data by accidental then we can restore it from the Exported/Imported data. Source:
Question: How do you initialize a VSAM file before any operation? a VSAM with alternate index?

Answer: Can write a dummy program that just opens the file for output & then closes it. Source:
Question: While designing vsam files,what's the best way to choose control interval size for the data and the index?

Answer: Well, it depends on whether the data will be accessed directly or sequentially.

for direct access use small ci

for sequential access use larger ci.
Question: What is Control Interval, Control Area ?

Answer: Control Interval is analogous to a physical block for QSAM files. It is the unit of i/o. Must be between 512 bytes to 32 k. Usually either 2K or 4K. A larger control interval increases performance for sequential processing while the reverse is true for random access. Under CICS when a record is locked, the entire CI gets locked.

Control area is a group of control intervals. CA is used during allocation. CA size is calculated based on the allocation type (cyl, tracks or records) and can be Source:

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