VSAM Interview Questions

VSAM stands for Virtual Storage Access Method. It is a file storage access technique used to organize data stored in Mainframes as files. Currently, there is a huge need for VSAM professionals who have good knowledge. In order to build VSAM careers, candidates must crack interviews successfully. 

In this article, MindMajix subject matter experts have consolidated a list of VSAM interview questions and divided the questions from basic to advanced based on complexity. This list would be helpful for both freshers, experienced professionals, FAQs & Tips 

• Freshers
• Experienced
• FAQs
• Tips For Interview

Top 10 Frequently Asked VSAM Interview Questions

• What types of objects are available in VSAM files?
• What are the different VSAM file types?
• Explain file status in VSAM.
• Which IDCAMS commands can be used with VSAM?
• Tell us about CI Split and CA Split.
• What does AMS perform in VSAM?
• What does "Cluster in VSAM" mean?
• What is GDG in VSAM?
• What is RDF in VSAM?
• What are the two major parts of VSAM?

VSAM Interview Questions For Freshers

1. What is VSAM?

Virtual Storage Access Method or VSAM, a file storage access method used in ZOS, MVS, and OS/90 operating systems. IBM introduced VSAM in 1970. It’s a high-performance access method that organizes data as files in mainframes.

Do you want to get certified and build your career in IBM DB2? Then enroll in "IBM DB2 Online Training" this course will help you to achieve excellence in this domain.

2. State variations between VSAM and Non-VSAM Files.

The following table illustrates the key differences between VSAM and non-VSAM files:

VSAM File	Non-VSAM Files
They require software to create, edit, or remove VSAM files.	Non-VSAM files can be created, edited, or deleted using the ISPF capability.
Supports data on a disc but is unable to handle data on other media, such as tapes.	File storage is possible on discs and tapes.
An ESDS, LDS, KSDS, or RRD files examples of a VSAM file.	BSAM files, flat files, QSAM files, sequential files, etc., are examples of non-VSAM files.
Data retrieval is facilitated with a well-organized index.	The disorganized index makes data retrieval time-consuming.
Data retrieval may be linear, dynamic, random, or sequential.	This support only sequential data retrieval.
This supports only the alternate index and the index.	This supports no indexes.
Datasets can be shared between different systems and geographical areas.	Datasets are kept locally.

3. What types of objects are available in VSAM files?

Each file in VSAM includes two objects, each of which specifies its storage system.

• Object FileBrowse: This object represents file browse actions. It entails using IDCAMS or TSO prompts to carry out the Enable, ResetBr, ReadNext, and ReadPrv methods.
• File object: It represents a single file. You can carry out operations like Read, Rewrite, Delete, UnlockWrite, and StartBr.

4. Describe the VSAM data set.

VSAM data sets to support different formats than non-VSAM data sets. The records in the VSAM data sets are organized into groups called CIs (control intervals). Records of VSAM are stored within the control interval, which is a limited storage space. A VSAM record’s length can be as long as 1 cylinder. In VSAM, Records are organized according to the relative record number, relative index key, or relative byte address.

Related Article: IBM DB2 Interview Questions

5. What are the different VSAM file types?

VSAM supports the following file types:

• Key-sequenced data set (KSDS) has records that are accessed by key-value pairs or relative byte addresses, and the records are arranged by the key field. Records in the KSDS dataset might have variable or fixed lengths.
• Entry-sequenced data sets or ESDS, are only reachable via relative byte addresses and include records either in the order of entry or in sequential order. Sequential data sets are similar to ESDSs. Records in ESDS datasets may be either fixed or variable in length.
• An unstructured data set with a Control Interval (CI) size greater than 4K makes up an LDS (Linear Data Set).
• The Relative Record Data Set or RRDS is a collection of records that may be accessed using their relative record number. Records are kept in slots with a specified length in RRDS databases.

6. What do you mean by the share option in VSAM?

VSAM Share Options controls users' access to VSAM datasets. Different users/jobs can be given various levels of access to a single VSAM dataset by making use of these parameters. 

The SHAREOPTS argument is written as SHAREOPTS in the DEFINE statement (a,b). Here, the letters a and b stand for the cross-region share option, which describes how two or more users or jobs on the same MVS system can share a file, and the cross-system share option, which describes how users or jobs on separate MVS systems can share a file. This value is typically SHAREOPTS (2 3).

Multiple users may handle the file concurrently if the cross-region value is 2, so long as only one of them is an updater. The file can be processed by any number of jobs or users, as indicated by the cross-system value of 3. (VSAM does not ensure integrity)

7. Explain file status in VSAM.

There is a chance that you will experience abends while working with VSAM databases. A VSAM file's status can be determined by its VSAM file status code. Before VSAM files may be opened for input or editing, they must first have at least one data record loaded into them.

8. How to convert a flat file into a VSAM file?

Using the steps listed below, you can convert flat files into VSAM:

• Step 1: Decide on your principal key first. You can also utilize the whole record as your primary key.
• Step 2: Sort the file using the primary key, or the full record, if none is supplied. Use a SORT statement to eliminate duplicates.
• Step 3: This step entails executing the JCL command IDCAMS - Define Cluster with the output from step 2 (the sorting methods) as input.
• Step 4: Lastly, use the IDCAMS REPRO command to load the flat file into VSAM.

9. State differences between ESDS and QSAM files.

Records are kept in sequential order, or in accordance with entry order, in both QSAM and ESDS files. The below table highlights the major differences between them:

QSAM Files	ESDS Files
ALTINDEX cannot exist in QSAM files (Alternate Index).	ALTINDEX can exist in ESDS files (Alternate Index).
It is feasible to create these files on tape.	On tape, ESDS files cannot be produced.

10. How do ESDS files store records?

The order in which records were added to the dataset is preserved in ESDS files. The records' physical address, often known as RBA, is used to refer to them (Relative Byte Address). 

If an ESDS dataset has 60 bytes per record, the first record's RBA would be 0, the second record's RBA would be 60, the third record's RBA would be 120, and so on. RBA enables addressed access or sequential access to records. 

The information is kept in the order that it was entered. At the conclusion, new records are added. The ESDS dataset does not allow for record deletion, although it does allow for inactive record marking. Records in the ESDS dataset may have a variable or fixed length.

11. Describe IDCAMS.

Integrated Data Cluster Access Method Services or IDCAMS, supports in manipulating VSAM datasets. It can be used to create, remove, and alter VSAM datasets.

12. When is it preferable to use a VSAM file versus a standard Sequential file?

A VSAM file would be favored over a Sequential file in a number of circumstances. To name a few:

• When a file is subjected to several actions based on a certain key value.
• When carrying out numerous operations on a file, like changing a particular record or deleting files.
• Whenever you require a file whose contents will frequently need to be changed (update, remove, or insert records).
• When several operations are necessary, such as when a record must be accessed in a number of ways, such as sequentially, with a key, or dynamically.

13. Is it possible to input an empty VSAM file into a Cobol program?

It is not possible to open a VSAM file that is empty or devoid of any records in order to utilize it as an input for a COBOL program. Users won't be able to access them anymore. Instead, a blank file might be opened for output. When the user opens the file, COBOL writes a fake record into it and removes it.

Releted Article: COBOL Interview Questions

14. Describe Freespace.

In the Define cluster, "Freespace" is a crucial parameter. This option specifies the percentage of freespace (available storage) that will be set aside for the data component's CI (control intervals) and CA (control areas). 0% is the default setting.

VSAM Interview Questions For Experienced

15. Which IDCAMS commands can be used with VSAM?

Using IDCAMS commands, a variety of actions can be performed on VSAM datasets. Some of the most helpful commands are listed below:

• Repro: Data is loaded into the VSAM dataset.
• Delete: Remove the catalogs, the VSAM, and non-VSAM datasets.
• Alter: Changes the VSAM file attributes ( path, cluster, catalog, etc.)
• Listcat: Gets information about the VSAM dataset catalog.
• Print: Prints the contents of a VSAM dataset.
• Repro: Data is loaded into the VSAM dataset.

16. How would you refer to the first generation in the JCL if a GDG has three generations?

Generation(0) denotes the GDG generation that is currently in effect, Generation(-1) denotes the GDG generation that came just before the current generation, and Generation(+1) denotes the GDG generation that comes after the current generation.

• The third generation of a GDG is the current generation, hence in JCL, we refer to it as generation(0) when there are three generations of a GDG.
• In JCL, generation(-1) refers to the generation (2nd generation) that came before the current generation (3rd generation).
• Last but not least, JCL uses generation(-2) to refer to the generation (1st generation) shortly before the 2nd generation.

Releted Article: JCL Interview Questions

17. Tell us about CI Split and CA Split.

CI and CA occur when new data records are inserted. If there is not enough space to fit a record in a CI than intended, the CI will split.

• CA SPLIT: When an addition or update is not possible in the current CI, it refers to the relocation or transfer of half of the records from one CA to another. Due to this, there are now two CAs that are roughly halfway full as opposed to one full and one empty.
• CI SPLIT: When an addition or update is not possible in the existing CI, it basically refers to the movement/transfer of some records from the existing CI to a free CI within the same CA.

18. How do you decide the optimal values for CI and free space?

The length of the record and the type of processing determines the Control Interval (CI) size. Most of the time, CI is 4K. If the record length exceeds 1K, then choose CI sizes of 6K or 8K. 

19. What does AMS perform in VSAM?

A service program known as an AMS (Access Method Service) can carry out a vast array of tasks on VSAM/Non-VSAM datasets and catalogs. IDCAMS, a potent utility program included with AMS, may be accessed via a common JCL and performs a wide range of AMS operations using its instructions. AMS uses two different types of commands:

Functional commands, such as DEFINE CLUSTER, REPRO, VERIFY, DELETE, BLDINDEX, and LISTCAT, demand actual action.

Modal instructions: These are commands that outline the prerequisites for carrying out functional ones like "IF-THEN-ELSE." Users using the Time Sharing Option (TSO) can only issue functional commands; modal commands are not allowed.

20. What do the terms Control Area (CA) and Control Interval (CI) mean?

Each data record is kept as a part of a unit called the Control Interval (CI) in the VSAM cluster's data component, and each Control Interval is stored in a unit called the Control Area (CA).

• Control area (CA): A control area (CA) is made up of numerous CI (Control intervals). A VSAM dataset may contain one or more CAs, depending on the quantity of records. Control intervals are divided into CAs, and data recordings are organized into CIs. Cylinders or disc tracks are used to measure the size of Control Areas.
• Control Interval (CI): Data records and other control information are kept in VSAM's Control Interval (CI), a contiguous storage space. In non-VSAM data management approaches, a block stands in for a unit of data being transferred between memory and storage devices. In VSAM, CI represents a unit of data exchanged between the memory (buffer) and storage device (DASD). When the cluster is defined, a control interval size is supplied. Control Intervals have a bytes-based size. for illustration, 2 kilobytes.

21. What does "Cluster in VSAM" mean?

The VSAM is made up of clusters, which are collections of datasets used to store data. A dataset's index, sequence set, and data sections are all categorized into clusters. Each VSAM cluster is located within an area that is separated into CIs, or contiguous regions (Control Intervals). There are two primary parts of a VSAM cluster:

• Index Component: The index part makes up this component. Using the index component, VSAM fetches records from the data component.
• Data Component: The data are located in this component. It includes the real recordings of data.

22. How can you resolve the issue when VSAM runs out of space?

If VSAM is out of space, you can solve the issue as follows:

• Make a new VSAM dataset with more space set aside.
• Using the IDCAMS REPRO command, transfer the old VSAM file into the new VSAM dataset.
• Using IDCAMS, modify, rename, or remove an old VSAM dataset.
• With IDCAMS, the name of the new VSAM dataset can be changed to match the name of the original VSAM dataset.

23.  What is VSAM Alternate Index?

In addition to the primary index, further indexes are made for the ESDS/KSDS datasets. Multiple keys can access records thanks to alternate indexes. The alternate index's key may include duplicates; it need not be unique.

24. What kinds of access options are available for the VSAM files?

For VSAM files, the following three access methods are available:

• Dynamic Access: To enable dynamic access, use the code ACCESS IS DYNAMIC in the FILE-CONTROL entry. Dynamic access combines sequential and random access inside the same application. One program can be created to carry out both sequential and random actions thanks to dynamic access, enabling some data to be accessed in sequential order and others dependent on their keys.
• Random Access: To enable random access, enter the code ACCESS IS RANDOM in the FILE-CONTROL entry. The value entered in a key field allows access to records inside indexed files, while the value entered in the relative key allows access to records within relative files.
• Sequential Access: To enable sequential access, use the code ACCESS IS SEQUENTIAL in the FILE-CONTROL entry. Records within relative files can be retrieved using their relative record numbers, and records within indexed files can be accessed using the key field chosen (either the primary key or an alternate key).

25. What is GDG in VSAM?

A GDG (Generation Data Group) is often made up of a number of linked non-VSAM data sets that are organized chronologically. Each dataset connected to the GDG base is referred to as a GDG version. These datasets are organized according to a common name known as the GDG base. There can be 255 generations in a GDG base. For processing data sets created on a regular basis, such as monthly, weekly, daily, and hourly, they are very efficient tools. The dataset is created in new generations with each processing cycle. There are a variety of uses for GDG, including, Statistics, Invoicing, Reporting, Audit Trails, Back-Up, etc.

VSAM FAQs

1. Which VSAM type is the fastest?

In general, using large CI and buffer space VSAM parameters may aid in enhancing the application's performance. Sequential access is the most effective compared to dynamic and random accesses.

2. What is status 23 in VSAM?

The file status 23 means the ‘file not found’. The record you try to access using a key is not found.

3. What is RDF in VSAM?

RDF is also known as Record Definition Fields. They describe record lengths and indicate how many adjacent records have a similar length. They are 3 bytes long.

4. What is the use of the verify command in VSAM?

The VERIFY command makes sure that the catalog accurately reflects the end of the VSAM data set when a VSAM data set is incorrectly closed as a result of an error. Owing to the inaccuracy, the catalog might have been incorrect. Additionally, the VSAM processing that was put on hold when the RECOVER option was inserted is finished by the VERIFY command.

5. What are the two major parts of VSAM?

The index component and data component are the two major parts of the VSAM cluster.

Index Component contains the indexes and helps in retrieving the records from the data component. Data Component contains the data records.

Tips to prepare for a VSAM Interview

Some of the preparation tips for VSAM interviews are as follows:

• Building a resume: Start by carefully building your resume. Everything you include in your resume should be expressed with confidence and clarity. Additionally, please make sure that your resume includes some VSAM-based Projects.
• Be well-prepared: In addition to VSAM-related technical questions, the interviewer might ask you some behavioral questions. Therefore, be sure to prepare for that as well.
• Research the company: This is a key tip that the majority of people miss. Start reading up on the company before heading to an interview. 
• Demonstrate your skills: Even if you are a technical guru, being unable to communicate effectively will become a huge disadvantage. Communication is a key ability.
• Give some real-world examples: In your responses, mention some real-world examples. This demonstrates to the interviewer that the candidate is aware of how to put theoretical concepts into practice.

Conclusion

These are some of the most common VSAM interview questions you could encounter while going through the interview process. In-depth technical knowledge is crucial for VSAM professionals, and these interview questions will provide you with some insight into key aspects.

Enrolling in our IBM DB2 Online Training will certainly improve your performance and help you ace your next interview.