Latest VSAM Interview Questions and Answers
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 purpose of VSAM?
VSAM acts as an interface between Application program & Operating System.
What is the maximum record length for the VSAM dataset?
Max size of a record in VSAM is cylinder = 2880 bytes approx.
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).
What are the advantages of VSAM?
Accessing the data is faster and easier.
VSAM supports more dataset types.
Supports variety of I/O Techniques.
Records can be accessed sequentially or randomly.
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.
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.
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.
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.
How to delete a member using JCL?
Using IDCAMS a member can be deleted. DELETE ‘XXX.YYY (memeber)
What is IDCAMS? and what is the purpose of it?
IDCAMS is an access method services utility used for creating, deleting, altering VSAM files and coping sequential file to a VSAM file, etc.
What are the optional parameters to the input dataset While loading the empty cluster with the data records?
2) TOADDRESS(address) where ‘address’ specifies the RBA value of the key of the input record.
3) FROMNUMBER (rrn)
4)TONUMBER (rrn) where ‘rrn’ specifies the relative record number of the RRDS record
5) FROMKEY (key)
6) TOKEY (key) where ‘key’ specifies the key of the input record
7) SKIP (number)
8) COUNT (number) where ‘number’ specifies the number of records to skip or copy Ex: REPRO INFILE(DD1) OUTFILE(DD2) SKIP(9000) COUNT(700)-Skips the first 9000 records and begin copying at 9001 and copies 700 records from DD1 to DD2.
What does the KEYRANGES parameter in Define Cluster commends do?
It divides a large dataset into several volumes according to the Key ranges specified. e.g. KEYRANGES ((0000001 2999999) (3000000 5999999)). if the activity on the key ranges are evenly distributed, concurrent access is possible, which is a performance improvement.
Describe SHAREOPTIONS parameter (SHR) in Define Cluster command?
It define the cross-region and cross-system sharing capabilities of the dataset. Syntax is SHR (Crvalue, CSvalue) value 1 means multiple read OR single write (read integrity ) 2 means multiple read AND single write ( Write integrity ) 3 means Multiple read AND multiple write 4 is same as 3, which refreshes the buffer with every random access default is SHR(1 3).
What is RECOVERY and SPEED parameters in DEFINE CLUSTER command?
RECOVERY (default ) and SPEED are mutually exclusive. Recovery pre-formats the control areas during the initial dataset load, if the job fails, you can restart but you must have a recovery routine already written to restart the job. SPEED does not pre-format the CAs. It is recommended that you specify SPEED to speed up your initial data load.
Is it slower if you access a record through ALT INDEX as compared to Primary INDEX?
Yes. Why Because the alternate key would first locate the primary key, which in turn locates the actual record. Needs twice the number of I/Os.
How many Alternate Indexes you can have on a dataset?
255 – but you must be a nut to have so many ALT Indexes on a dataset!
On which dataset You can have ALT INDEX?
Only on KSDS and ESDS – not RROS
What is the meaning of VSAM RETURN-CODE 28?
Out of space condition is raised.
How do you fix the problem associated with VSAM out of space condition?
Define new VSAM dataset allocated with more space.
Use IDCAMS to REPRO the old VSAM file to new VSAM dataset.
Use IDCAMS to ALTER / rename the old VSAM dataset or se IDCAMS to DELETE the old VSAM datset.
Use IDCAMS to ALTER / rename the new VSAM dataset to the name of the original VSAM dataset.
During processing of a VSAM file, some system error occurs and it is subsequently unusable What do you do?
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?
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.