Virtual Storage Access Method (VSAM)

Q51) How do you calculate record size of an alternate cluster? Give your values for both unique and nonunique.Q51) Unique Case: 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

Q52) What is the difference between sequential files and ESDS files?Q52) 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.

Q53) How do you load a VSAM data set with records ?Q53) Using the REPRO command.

Q54) How do you define a GDG ?Q54) 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)

Q55) Do all versions of the GDG have to be of the same record length ?Q55) No, the DCB of the model dataset can be overridden when you allocate new versions.

Q56) How are different versions of GDG named ?Q56) base-file-name.GnnnnnV00 where nnnn= generation number (upto 255). nnnn will be 0000 for the 1st generation.

Q57) Suppose 3 generations of a GDG exist. How would you reference the 1st generation in the JCL? - GSQ57) Use GDG name(-2).

Q58) 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? - GSQ58) 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.

Q59) What more info you should give in the DD statement while defining the next generation of a GDG? - GSQ59) 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.

Q60) Assuming that the DEFINE JCL is not available, how do you get info about a VSAM file's organisation?Q60) Use the LISTCAT command.

Q61) During processing of a VSAM file, some system error occurs and it is subsequently unusable . What do you do ?Q61) Run VERIFY.

Q62) How do you fix the problem associated with VSAM out of space condition?Q62) 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 dataset.

Use IDCAMS to ALTER / rename the new VSAM dataset to the name of the original VSAM dataset.

Q63) What is the meaning of VSAM RETURN-CODE 28?Q63) Out of space condition is raised.

Q64) On which datasets You can have ALT INDEX?.Q64) only on KSDS and ESDS - not RRDS

Q65) How many Alternate Indexes you can have on a dataset?Q65) 255 - but you must be a nut to have so many ALT Indexes on a dataset!

Q66) Is it slower if you access a record through ALT INDEX as compared to Primary INDEX?Q66) 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.

Q67) What is RECOVERY and SPEED parameters in DEFINE CLUSTER command?Q67) RECOVERY (default) and SPEED are mutually exclusive. Recovery preformats 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 preformat the CAs. It is recommended that you specify SPEED to speed up your initial data load.

Q68) Describe SHAREOPTIONS parameter (SHR) in Define Cluster command.Q68) It defines 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).

Q69) What does the KEYRANGES parameter in Define Cluster commend do?A69) 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.

Q70) What are the optional parameters to the input dataset While loading the empty cluster with the data records?70) 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 begins copying at 9001 and copies 700 records from DD1 to DD2.

Q71) What is IDCAMS? and what is the purpose of it?.A71) IDCAMS is an access method services utility used for creating, deleting, altering VSAM files and copying sequential file to a VSAM file, etc.

Q72) How to delete a member using JCL.A72) Using IDCAMS a member can be deleted. DELETE 'XXX.YYY(member)

Q73) What is the Difference between LDS & ESDS ?A73) These two datasets are VSAM datasets. ESDS maintains control information. But LDS does not maintains the control information.

Q74) Is a delete operation possible in an ESDS?B. Is rewrite operation possible in ESDS ?A74) No delete operation is not possible in VSAM ESDS.B. Yes rewrite operation is possible in an ESDS.

Q75) What is an alternate index and path ?A75) 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.