No, they would not be left empty. one record will be written in each CI and 1 CI will be written for each CA.
The Index and data components of a KSDS
3. What is the RRN for the first record in RRDS?
The answer is : 1
5. What is the device independent method to indicate where a Record is Stored?
By USING RBA (Relative Byte Address).
6. What is the biggest disadvantage of using a VSAM dataset?
FREE SPACE ( FPSC )
7. How many buffers are allotted to VSAM KSDS and ESDS?
2 data buffers by default for ESDS. For KSDS it allots 2 data buffers and 1 index buffers. each buffer is about 4K.
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.
11. How to delete a member using JCL?
Using IDCAMS a member can be deleted. DELETE 'XXX.YYY (memeber)
12. 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.
1) FROMADDRESS(address)
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.
14. 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 inprovement.
15. 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 defualt is SHR(1 3).
16. What is RECOVERY and SPEED parameters in DEFINE CLUSTER command?
RECOVERY (default ) and SPEED are mutually exclusive. Recovery performats the control areas during the initial dataset load, if the job fails, you can restatt but you must have a recovery routine already written to restart the job. SPEED does not preformat the CAs. It is recommended that you specify SPEED to speed up your initial data load.
17. 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.
18. 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 !
19. On which dataset You can have ALT INDEX?
only on KSDS and ESDS - not RROS
20. What is the meaning of VSAM RETURN-CODE 28?
Out of space condition is raised.
21. 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.
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.
24. How are different versions of GDG named?
base-file-name. GnnnnnnV00 where nnnn=generation number (upto 255). nnnn will be 0000 for the 1st generation.
Use the DEFINE GENERATIONDATAGROUP command. In the same IDCAMS step, another dataset must be defined whose DCB parameters are used when new generations of the GDG are created. This dataset is known as the model dataset. The DS name of this model dataset must be the same as that of the GDG, so use a disp of keep rather than catlg and also specify space = (trk,0)
26. What is the difference between sequential files and ESDS files?
Sequential (QSAM) files can be created on tape while ESDS files cannot. Also, you can have ALTINDEX for an ESDS while no such facility exists for QSAM files.
UniqueCase: 5 + (alt-key-length + primary - key )
Non unique Case: 5 + (alt-key-length + n * primary - key ) where n = number of duplicate records for the alternate key
28. How do you load a VSAM data set with records?
Using the REPRO command.
29. Do all versions of the GDG have to be of the same record length?
No, the DCB of the model dataset can be overridden when you allocate new versions.
30. Suppose 3 generations of a GDG exist. How would you reference the 1st generation in the JCL?
Use GDG name(-2).
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.
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.
