TOP VSAM Part7 Interview Questions and Answers

61. In the COBOL SELECT statement for a KSDS what are the three possibilities for ACCESS?
ACCESS can be SEQUENTIAL, RANDOM or DYNAMIC.

62. Do primary key values have to be unique? Do alternate key values have to be unique?
Primary key values must be unique; alternate key values need not be.

63. 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.

64. What is the upgrade set?
The upgrade set is the list of all AIXes that VSAM must maintain for a specific base cluster, so that when data in the base cluster is updated, the AIX files are also updated.

65. What is an alternate index?
An AIX is a file that allows access to a VSAM dataset by a key other than the primary one.

66. What is a cluster?
A cluster is the combination of the index, sequence set and data portions of the dataset. The operating system gives program access to the cluster, ie. to all parts of the dataset simultaneously.

67. What is a sequence set?
This is the part of the index that points to the CA and CI of the record being accessed.

68. What are the distinctive features of a KSDA, key sequenced dataset?
The index and the distributed free space.

69. How are records stored in an ESDS, entry sequenced dataset?
they are stored without respect to the contents of the records and in the order in which they are included in the file.

70. What are the types of VSAM datasets?
Entry sequenced dataset (ESDS), key sequenced datasets (KSDS) and relative record dataset (RRDS).

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VSAM Part4 Questions and Answers

31. 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.

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

33. Using Alternate Indexes in CICS program?
FCT entires 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.

34. 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 ...

35. 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.

36. 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.

37. What are the three levels of definition for the VSAM DEFINE?
They are DEFINE CLUSTER, DATA and INDEX.

38. What is the utility program closely associated with VSAM?
IDCAMS, the access mehtod services utility.

39. 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.

40. 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.

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70 TOP VSAM Interview Questions and Answers

1. What are the different types of VSAM files available?
ESDS: Entry Sequence Data Set
KSDS: Key Sequence Data Set
RRDS: Relative Data Set

2. what is purpose of VSAM?
VSAM acts as an interface between Application program & Operating System.

3.What is the maximum record length for the VSAM dataset?
Max size of a record in VSAM is cylinder = 2880 bytes approx.

4.What is File Status in VSAM?
The File STATUS clause of the FILE-CONTROL paragraph allows for each file to be associated with afile status key (i.e., the 2-character data item specified in the FILE STATUS clause). If the FILE STATUS clause is specified for a given file, a value indicating the status of each I/O operation against that file is placed in the accociated file status key. This value is stored in the file statuskey as soon as the I/O operation is completed (and before execution of any EXCEPTION/ERROR declarative or INVALIDKEY/AT END phrase associated with the I/O request).
Note: This element may behave differently when the CMPR2 compiler option is used. The file statuskey is divided into two status keys: the first character is known as file status key1; the second character is file status key 2.

5. 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).

6. 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.

7. 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.
     
8. What is an alternate index and path?
An alternate index is an another way of accessing key sequenced data record stored in a base cluster and path is the linkage which connect alternate index to its base cluster.

9. 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.

10. What is the difference between LDS and ESDS?
There two datasets are VSAM datasets. ESDS maintains control information. But LDS does not maintains the control information.

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