Top Most Cobol And DB2 Interview Questions Part – 5
What Is Vsam?
VSAM = Virtual Storage Access Method
Virtual storage access method (VSAM) an IBM disk 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. Originally a recordoriented filesystem.[NB 2], VSAM comprises four[NB 2] data set organizations: Key Sequenced Data Set (KSDS), Relative Record Data Set (RRDS), Entry Sequenced Data Set (ESDS) and Linear Data Set (LDS).
What Are The Different Types Of Vsam Files Available?
ESDS:
Entry Sequence Data Set
KSDS:
Key Sequence Data Set
RRDS:
Relative Data Set
What Is Idcams?
IDCAMS is the Access Method Services program. You run the IDCAMS program and supply AMS commands thru SYSIN. (examples of AMS commands are DELETE, DEFINE, REPRO etc..).
What Is Control Interval, Control Area?
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 max of 1 cylinder
What Is Freespace?
Coded in the DEFINE as FREESPACE(ci ca) where ci is the percentage of each control interval to be left free for insertions, ca is the percentage of control intervals in each control area to be left empty.
How Do You Decide On Optimum Values For Ci, Freespace Etc?
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.
Would You Specify Freespace 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 Shareopts?
SHAREOPTS is a parameter in the DEFINE and specifies how an object can be shared among users. It is coded as SHAREOPTS(a b), where a is the cross region share option ie how two or more jobs on a single system can share the file, while b is the cross system share option ie how two or more jobs on different MVSes can share the file. Usual value is (2 3).
Explain What Is Jcl?
JCL stands for Job Control Language. It is the command language of Multiple Virtual Storage (MVS). It is the normally used in Operating System in the IBM Mainframe computers.
Explain What Is The Use Of Jcl?
It is used for the deleting creating, the Data Sets, GDG’S and VSAM clusters.
It is used for comparing the files and PDS members
It is used for compiling and executing the programs which includes batch programs as well
It is used for merging and sorting on file data
Mention The Types Of Job Control Statements?
The types of job control statements are
JOB – to identify the Job
DD – to supply the I/O files needed for the execution of the program
EXEC – to identify which program has to be executed
Explain How Jcl Works?
JCL recognizes the program to be executed, the inputs that are required and location of the input/output and informs the Operating System through Job control Statements.
Mention What Is The Jcl Statement Consists Of?
JCL statement consists of
Name field (optional)
Operation field
Operand
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What Is The Syntax Of Jcl Statement?
The syntax of JCL statement is,
//Job-name JOB Positional-param, Keyword-param
Explain What Is Dd Statement Is Used In Jcl?
DD statement is used in JCL is used to identify the source of input and the placement of output information.