Are you prepared in attending an interview? We are there to guid you on how to prepare for the interview and what sort of questions are being asked. If you are preparing for IBM - VSAM job interview then do check out our Wisdomjobs page to get latest interview questions on IBM - VSAM. The VSAM method is an access method that is used in managing several user data types. This provides very robust and complex functions that creates a record which is not understandable by different access methods. Major data sets: key-sequenced, entry-sequenced, linear, or relative record. Below is the list of frequently asked IBM - VSAM interview questions and answers which gets you ready to face the interviews without worrying about difficulty:
Question 1. What Is An Alternate Index ?
Answer :
An alternate index is another file related to the cluster, but sorted using an alternate key that can have duplicates.
Question 2. How Do You Create An Alternate Index ?
Answer :
You use the IDCAMS utility with the DEFINE AIX option after you build the cluster and then do another IDCAMS with the BLDINDEX option to populate the alternate index.
Answer :
The RECORDSIZE parameter. There are 2 numbers that follow this: the 1st is the average and the 2nd is the maximum. The values are equal to 5 + (cluster key length) + N*(alternate key length), where N is the allowable number of duplicates.
Question 4. Name A Few Common Vsam Status Codes?
Answer :
00-OK
02-READ a duplicate alternate key
10-end of file reached while doing a READ
22-trying to WRITE a duplicate primary key
23-record not found while doing a READ
97-file integrity verified, do an IDCAMS VERIFY
Question 5. What Is Buffering And How Does It Apply To Vsam Files ?
Answer :
When large blocks of data are used, more main storage is required than when smaller blocks are used, but large blocks save CPU time and disk space. Additionally, extra buffers may save elapsed time since the program does not have to wait for an I/O to complete for it to continue processing.
In the JCL, you specify BUFNI (number of index buffers) and BUFND (number of data buffers) as sub parameters of the AMP parameter.
For random access, the BUFNI is one more than the number of index levels and a BUFND of 2 is fine.
For sequential access, a BUFNI of 1 and a minimum of 5 for BUFND is fine.
For dynamic access, the values of each is the higher of the numbers for either random or sequential.
Question 6. What Are The Different Types Of Vsam Files Available?
Answer :
ESDS: Entry Sequence Data Set
KSDS: Key Sequence Data Set
RRDS: Relative Data Set
Answer :
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..).
Question 8. Can Ams Commands Be Run From The Tso Prompt ?
Answer :
Yes
Question 9. Syntax Of Ams Modal Commands ?
Answer :
Note: these can be used only under IDCAMS and not from the TSO prompt.
IF LASTCC(or MAXCC) >(or <,= etc..) value - THEN - DO -
command set (such as DELETE, DEFINE etc..)
ELSE - DO -
command set
LASTCC - Condition code from the last function(such as delete) executed
MAXCC - Max condition code that was returned by any of the prev functions
SET is also a valid AMS command. SET LASTCC (or MAXCC) = value
The maximum condition code is 16. A cond code of 4 indicates a warning. A cond code of 8 is usually encountered on a DELETE of a dataset that is not present.
Answer :
The maximum condition code generated is returned as the condition code of the IDCAMS step.
Question 11. What Is Control Interval, Control Area ?
Answer :
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
Question 12. What Is Freespace ?
Answer :
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.
Question 13. How Do You Decide On Optimum Values For Ci, Freespace Etc..?
Answer :
CI size should be based on record length, type of processing. Usually CI is 4K. If record length is larger(>1K), choose 6K or 8K.
FREE SPACE 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.
Question 14. Would You Specify Freespace For An Esds?
Answer :
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.
Question 15. What Is Shareopts ?
Answer :
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).
Question 16. What Is The Meaning Of Each Of The Values In Shareopts(2 3)?
Answer :
Value of 2 for cross region means that the file can be processed simultaneously by multiple users provided only one of them is an updater. Value of 3 for cross system means that any number of jobs can process the file for input or output (VSAM does nothing to ensure integrity).
Question 17. How Do You Define A Ksds ?
Answer :
DEFINE CLUSTER(cluster name) with the INDEXED parameter. Also specify the ds name for the DATA component & the ds INDEX component. Other important parms are RECORDSIZE, KEYS, SHARE OPTIONS.
Question 18. How Do You Define An Altindx ? How Do You Use Altindxs In Batch, Cics Pgms ?
Answer :
DEFINE ALTERNATEINDEX. Important paramters are RELATE where you specify the base cluster name, KEYS, RECORDSIZE, SHAREOPTIONS,UNIQUEKEY(or NONUNIQUEKEY), DATA(ds name for the data component), INDEX(ds name for the index component).
Then DEFINE PATH. Important paramters are NAME (ds name for the path), PATHENTRY (ds name of the alternate index name), UPDATE(or NOUPDATE) which specifies whether an alt index is updated when a update to the base cluster takes place.
Then BLDINDEX. Parameters are INDATASET(ds name of base cluster), OUTDATASET(ds name of AIX).
Using alternate indexes in batch pgms:
In the JCL, you must have DD stmts for the cluster and for the path(s). In the cobol pgm, SELECT .. ASSIGN TO ddname for base cluster RECORD KEY IS... ALTERNATE RECORD KEY IS..
Using alternate indexes in CICS pgms:
FCT entries must be created for both base cluster & the path. To read using the alternate index, use the dd name of the path in CICS file control commands.
Question 19. What Happens When You Open An Empty Vsam File In A Cobol Program For Input?
Answer :
A VSAM file that has never contained a record is treated as unavailable. Attempting to open for input will fail. An empty file can be opened for output only. When you open for output, COBOL will write a dummy record to the file & then delete it out.
Question 20. How Do You Initialize A Vsam File Before Any Operation? A Vsam With Alternate Index?
Answer :
Can write a dummy program that just opens the file for output & then closes it.
Question 21. What Does A File Status Of 02 On A Vsam Indicate?
Answer :
Duplicate alternate key . Happens on both input and output operation
Answer :
Unique Case: 5 + ( alt-key-length + primary-key )
Nonunique Case: 5 + ( alt-key-length + n * primary-key )
where n = # of duplicate records for the alternate key
????Any one who knows - can you explain ?
Question 23. What Is The Difference Between Sequential Files And Esds Files?
Answer :
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.
Question 24. How Do You Load A Vsam Data Set With Records ?
Answer :
Using the REPRO command.
Question 25. How Do You Define A Gdg ?
Answer :
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)
Question 26. Do All Versions Of The Gdg Have To Be Of The Same Record Length ?
Answer :
No, the DCB of the model dataset can be overridden when you allocate new versions.
Question 27. How Are Different Versions Of Gdg Named ?
Answer :
base-file-name.GnnnnnV00 where nnnn= generation number (upto 255).
nnnn will be 0000 for the 1st generation.
Answer :
Use GDG name(-2).
Answer :
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.
Answer :
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.
Answer :
Use the LISTCAT command.
Answer :
Run VERIFY.
Answer :
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..).
Question 34. Can Ams Commands Be Run From The Tso Prompt?
Answer :
Yes
Question 35. Syntax Of Ams Modal Commands?
Answer :
Note: these can be used only under IDCAMS and not from the TSO prompt.
IF LASTCC(or MAXCC) >(or <,= etc..) value - THEN - DO -
command set (such as DELETE, DEFINE etc..)
ELSE - DO -
command set
LASTCC - Condition code from the last function(such as delete) executed
MAXCC - Max condition code that was returned by any of the prev functions
SET is also a valid AMS command. SET LASTCC (or MAXCC) = value
The maximum condition code is 16. A cond code of 4 indicates a warning. A cond code of 8 is usually encountered on a DELETE of a dataset that is not present.
Answer :
The maximum condition code generated is returned as the condition code of the IDCAMS step.
Question 37. What Is Control Interval, Control Area?
Answer :
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
Question 38. What Is Freespace?
Answer :
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.
Question 39. How Do You Decide On Optimum Values For Ci, Freespace Etc?
Answer :
CI size should be based on record length, type of processing. Usually CI is 4K. If record length is larger(>1K), choose 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.
Question 40. What Is Shareopts?
Answer :
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).
Question 41. How Do You Define A Ksds?
Answer :
DEFINE CLUSTER(cluster name) with the INDEXED parameter. Also specify the ds name for the DATA component & the ds INDEX component. Other important parms are RECORD SIZE, KEYS, SHARE OPTIONS.
Question 42. How Do You Define An Altindx ? How Do You Use Altindxs In Batch, Cics Pgms?
Answer :
DEFINE ALTERNATEINDEX. Important parameters are RELATE where you specify the base cluster name, KEYS, RECORDSIZE, SHAREOPTIONS, UNIQUEKEY (or NONUNIQUEKEY), DATA(ds name for the data component), INDEX(ds name for the index component).
Then DEFINE PATH. Important paramters are NAME (ds name for the path), PATHENTRY (ds name of the alternate index name), UPDATE(or NOUPDATE) which specifies whether an alt index is updated when a update to the base cluster takes place.
Then BLDINDEX. Parameters are INDATASET(ds name of base cluster), OUT DATASET(ds name of AIX).
Using alternate indexes in batch pgms:
In the JCL, you must have DD stmts for the cluster and for the path(s). In the cobol pgm, SELECT .. ASSIGN TO ddname for base cluster RECORD KEY IS... ALTERNATE RECORD KEY IS..
Using alternate indexes in CICS pgms:
FCT entries must be created for both base cluster & the path. To read using the alternate index, use the dd name of the path in CICS file control commands.
Answer :
Can write a dummy program that just opens the file for output & then closes it.
Question 44. What Are The Types Of Vsam Datasets?
Answer :
Entry sequenced dataset (ESDS), key sequenced data sets (KSDS) and relative record dataset (RRDS).
Question 45. If You Wish To Use The Rewrite Command How Must The Vsam File Be Opened?
Answer :
It must be opened as I/O.
Question 46. What Is File Status In Vsam?
Answer :
The File STATUS clause of the FILE-CONTROL paragraph allows for each file to be associated with a file 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 associated file status key. This value is stored in the file status key as soon as the I/O operation is completed (and before execution of any EXCEPTION/ERROR declarative or INVALID KEY/AT END phrase associated with the I/O request).
Note: This element may behave differently when the CMPR2 compiler option is used. The file status key is divided into two status keys: the first character is known as file status key1; the second character is file status key 2.
Question 47. What Are The Different Types Of Vsam Files Available? Explain Them
Answer :
Virtual Storage Access Method(VSAM) is a disk storage system.
It was implemented in OS/VS2 operating system.
Subsequently, it was used through out the MVS architecture.
VSAM comprises of the following access methods:
ESDS: Entry Sequence Data Set
KSDS: Key Sequence Data Set
RRDS: Relative Data Set
VSAM records can be of fixed or variable length.
These are organized in fixed size blocks, known as Control Intervals, and later into larger divisions known as Control Areas.
CI sizes are measured in terms of bytes, while CA sizes are measured in terms of disk tracks or cylinders.
ESDS : It contains the files which are interface specific and
accessed through Relative Byte Address
KSDS : It contains the files which are interface specific and accessed through a secondary index
RRDS : It contains the files which are interface specific and accessed through Relative Record Number
Each file has two objects.
DELETE,READ,REWRITE,UNLOCK,WRITE,STARTBR operations.
ENDBR,READNEXT,READPREV,RESETBR
Question 48. What Is The Syntax Of Ams Modal Commands?
Answer :
The following is the syntax of AMS modal commands:
IF LASTCC(or MAXCC) >(or <,= etc..) value - THEN - DO -
command set (like DELETE, DEFINE etc..)
ELSE - DO -
command set
where
LASTCC - Condition code from the last function(such as delete) executed
MAXCC - Max condition code that was returned by any of the prev functions
SET is also a valid AMS command. SET LASTCC (or MAXCC) = value
PS: These can be used only under IDCAMS and not from the TSO prompt.
Question 49. How Do You Define An Altindx ? How Do You Use Altindxs In Batch, Cics Programs?
Answer :
Using alternate indexes in batch programs:
JCL, has DD statements for cluster and for paths.
For the COBOL program :
The command SELECT ASSIGN TO ddname For the base cluster RECORD KEY IS...... ALTERNATE RECORD KEY IS… used
Using alternate indexes in CICS programs:
The creation of FCT entries are mandatory for both cluster and the path
Utilize the dd name of the path in CICS file control commands, by using the alternate index
Answer :
KSDS cluster can be defined by
-Using the file-aid
-or by using IDCAMS utility:
The record can be defined with average length of 100 and maximum length of 150, in IDCAMS, with key length 10 starting at 0.
The following example illustrates :
//step01 EXEC pgm=IDCAMS
//SYSIN DD *
DEFINE CLUSTER(NAME(userid.name.sample) -
VOLUMES(MVS801) -
RECORDSIZE(100 150) -
TRACKS(10 20)
KEYS(10 0) -
INDEXED ) -
DATA ( NAME(userid.name.sample.data)) -
INDEX( NAME(userid.name.sample.index)) -
/*
//
Question 51. How Do You Convert Flat Files To Vsam Files?
Answer :
Flat files are converted into VSAM files by following process:
Question 52. How Did You Refresh A Vsam File And How Frequently You Do It ?
Answer :
Step 1: Deleting the existing VSAM file:
IF LASTCC =8 ; SET MAXCC=0
Step 2: DEFINE VSAM-FILE(COND=(0,LT,STEP1)
Return-code = 8 when the file that is trying to delete does not exist.
Utilize the command VERIFY in TSO
Question 53. Explain The Information Contained In Ci
Answer :
Question 54. Explain The Differences Between Vsam And Non-vsam Files
Answer :
A data set is a physical records that are stored on a disk or tape , is a collection with a unique name
The data set is normally identified by the MVS with labels
The label information need to be supplied in JCL
The data set organization in NON-VSAM files are sequenced, Indexed Sequential, Direct and partitioned
Question 55. Difference Between Vsam And Database Tables
Answer :
Question 56. What Is Meant By Dirty Read In Vsam?
Answer :
Question 57. What Are The Idcams Commands That Can Be Used For Vsam And Explain Each Of Them.
Answer :
Question 58. What Is The Purpose Of The Verify Function Of Idcams?
Answer :
To re-sync the end of the file information with the catalog information, the VERIFY function is used.
IBM - VSAM Related Tutorials |
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Change Management Tutorial | IBM DB2 Tutorial |
COBOL Tutorial | IBM-JCL Tutorial |
IBM Mainframe Tutorial | IMS/DB Tutorial |
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