Introduction to VSAM Interview Questions and Answers
VSAM stands for “Virtual Storage Access Method”. This was introduced by IBM in the 1970s. It is a file storage access method used in MVS, z/OS and OS/390 version of operating systems. VSAM helps in organizing the data in the form of files in Mainframe computers. “VSAM are accessed method used in operating systems (like MVS, z/OS, and OS/360) to perform needful operations”
A sequential approach for easy understanding, so to start with let’s see what a mainframe is and how it differs from a supercomputer.
Both have different application domain – mainframes excel in reliable volume (i.e. integer operations like financial, indexing and comparison) whereas Supercomputers are designed to perform floating-point operations like arithmetic operations with precision.
Now, Mainframes were first introduced in the 1940s by vendors like IBM, Hitachi, and Amdahl. These have special characteristics like large size, storage amount, processing power and high level of reliability. These are designed to handle very high volume input and output (I/O). A single Mainframe has the power to replace dozens or even hundreds of smaller servers.
So, these mainframe computers have specially designed OS to support their wide operation capability. These OS are-
- MVS
- z/OS
- OS/390
So, if this huge volume of data is under consideration then there must be some manipulation technique. This is where VSAM enters into the picture.
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Now, if you are looking for a job which is related to VSAM then you need to prepare for the 2019 VSAM Interview Questions. It is true that every interview is different as per the different job profiles. Here, we have prepared the important VSAM Interview Questions and Answers which will help you get success in your interview.
In this 2019 VSAM Interview Questions article, we shall present 10 most important and frequently asked VSAM Interview questions. These questions are divided into two parts are as follows:
Part 1 – VSAM Interview Questions (Basic)
This first part covers basic VSAM Interview Questions and Answers
Q1. What are VSAM Commands?
Answer:
VSAM commands are used to perform operations on the datasets of VSAM. These commands are used to manipulate the datasets as per the need.
Some of the most important and useful VSAM commands are
- Alter: to modify the file attributes of the VSAM
- Repro: used to load data in VSAM dataset and also to copy from one VSAM dataset to another
- Listcat: Helps in fetching the catalog details of a VSAM datasets
- Examine: to verify the structural integrity of a key-sequenced data set cluster.
- Verify: to crosscheck and verify to fix VSAM files which may not be closed in a proper way due to error.
Q2. Quickly go through the VSAM commands syntax as-well?
Answer:
- Alter: ALTER file-cluster-name [password]
- Repro: REPRO INFILE (in-ddname)
OUTFILE (out-ddname)
- Listcat: LISTCAT ENTRY (vsam-file-name) ALL
- Examine: EXAMINE NAME (vsam-ksds-name)
INDEX TEST DATASET
ERRORLIMIT (50)
- Verify: VERIFY DS (vsam-file-name)
Let us move to the next VSAM Interview Questions.
Q3. Which are the main components of a VSAM?
Answer:
There are 3 main components of a VSAM-
- VSAM cluster
- Control Area
- Control Interval
Q4. In response to a database, what are the available types of VSAM datasets?
Answer:
This is the basic VSAM Interview Question asked in an interview. There are 3 types of VSAM databases namely
- ESDS: Entry sequenced datasets
- KSDS: Key sequenced datasets
- RRDS: Relative record datasets
Q5. How are the records stored in ESDS?
Answer:
In ESDS the records are stored in the order of which they are included in the file. One thing to remember, they are not stored with respect (w.r.t) to a content of the record.
Q6. What is a cluster?
Answer:
A cluster combines all of these – index, sequence set and the data part of the dataset within it. The responsible OS gives the program access of the cluster (access is given to every part of the dataset simultaneously).
Q7. What do you think will be the output if an empty VSAM file is opened in a COBOL program?
Answer:
Opening a VSAM file that has no record in it is not possible. It will become unavailable for the user trying to do so.
Rather, an empty file can be opened for the purpose of some outputs. COBOL will write a dummy record in the file and delete it when a user opens it for some output.
Part 2 – VSAM Interview Questions (Advanced)
Let us now have a look at the advanced VSAM Interview Questions.
Q8. What kind of problems are associated with the VSAM out of space conditions?
Answer:
– In defining a new VSAM dataset while allocating more space to ti
– In REPRO the old VSAM file to new VSAM dataset with IDCAMS
– While ALTER/rename the old dataset using IDCAMS
– One can also use the IDCAMS to ALTER the new VSAM dataset to the original VSAM dataset.
Q9. What will you understand with the following command?
Answer:
Command “VSAM RETURN-CODE 28”
This will raise out of space conditions in the datasets
Let us move to the next VSAM Interview Questions.
Q10. According to you, what can be the biggest disadvantages of using the VSAM datasets?
Answer:
In my opinion, the biggest disadvantages will be the FREESPACE(FPSC).
Q11. Name a few VSAM File status codes?
Answer:
This is the frequently asked VSAM Interview Questions in an interview. There are some VSAM File Status Codes
- 00 – Operation completed completely
- 04 – Invalid fixed length record
- 22 – Primary duplicate key found
Q12. What is IDCAMS?
Answer:
IDCAMS is an access method service program. A user runs the IDCAMS program by supplying the AMS command through SYSIN. Some of the crucial AMS commands are DELETE, DEFINE, and REPRO.
Q13. How to define KSDS?
Answer:
This can be done by defining the cluster with the indexed parameter. Also, to specify the DS name for the related components and the DS index components.
Let us move to the next VSAM Interview Questions.
Q14. How do you load a VSAM dataset with Records?
Answer:
By using the REPRO command
Q15. Explain the KSDS file structure?
Answer:
Unique key (value) is there to find any specific records. There is Index Components and Data Components. The key value is searched in the Index section. Once it is searched the corresponding memory address is retrieved. Actual data will be fetched once this process ends and the user will be left with the following details –
Let’s see the following structure –
INDEX COMPONENTS
| KEY | MEMORY ADDRESS |
| Key 1 | 245 |
| Key 2 | 100 |
DATA COMPONENTS
| MEMORY ADDRESS | KEY | RECORD FILE 1 | RECORD FILE 2 |
| 400 | KEY 3 | Attendances | XXXX |
| 200 | KEY 1 | ID’s | 12345 |
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