Virtual Storage Access Method (VSAM)

Q26) What is a VSAM slot?Q26) A relative record dataset (RRDS) consists of a specified number of areas called slots. Each slot is identified by a relative record number (RRN) which indicates its relative position in the file.

Q27) What is the utility program closely associated with VSAM?Q27) IDCAMS, the access method services utility.

Q28) There are at least seven IDCAMS commands; name and explain each of them ?.Q28) ALTER modifies information for a catalog, alternate index, cluster or path. BLDINDEX builds the alternate index, of course. DEFINE is used for ALTERNATEINDEX, CLUSTER or PATH. DELETE removes the catalog entry for a catalog, cluster, alternate index or path. LISTCAT lists information about the dataset. PRINT prints the dataset contents. REPRO copies records from one file to another.

Q29) What are the three levels of definition for the VSAM DEFINE?Q29) They are DEFINE CLUSTER, DATA and INDEX.

Q30) What is the significance of the SHAREOPTIONS parameter?Q30) It specifies how the file may be shared between jobs and between batch and CICS environments.

Q31) What is the meaning of the DEFINE MODEL parameter?Q31) It specifies whether Daniela Pestova or Yamila - oops! Wrong models! The MODEL parameter allows you to model your cluster by modeling it after an existing cluster.

Q32) What is File Status in VSAM?Q32) 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 INVALIDKEY/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 key 1; the second character is file status key 2.

Q33) What's a LDS (Linear Data Set) and what's it used for?Q33) LDS is a VSAM dataset in name only. It has unstructured 4k (4096 bytes) fixed size CI’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.

Q34) What is IDCAMS ?Q34) 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..).

Q35) Can AMS commands be run from the TSO prompt ?Q35) Yes

Q36) Syntax of AMS modal commands ?Q36) 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.

Q37) Under IDCAMS , multiple functions can be executed, each of which returns a cond code. What will be the condition code returned to the operating system ?Q37) The maximum condition code generated is returned as the condition code of the IDCAMS step.

38) What is Control Interval, Control Area?Q38) 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

Q39) What is FREESPACE ?Q39) 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.

Q40) How do you decide on optimum values for CI, FREESPACE etc...?Q40) 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.

Q41) Would you specify FREESPACE for an ESDS?Q41) 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.

Q42) What is SHAREOPTS ?Q42) 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 MVS’s can share the file. Usual value is (2 3).

Q43) What is the meaning of each of the values in SHAREOPTS(2 3)?Q43) 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).

Q44) How do you define a KSDS ?Q44) 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, SHAREOPTIONS.

Q45) How do you define an ALTINDX ? How do you use ALTINDXs in batch, CICS pgm’s ?Q45) 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).

Q46) Using Alternate Indexes in Batch pgms:Q46) In the JCL, you must have DD stmts for the cluster and for the path(s). In the COBOL Program, SELECT .. ASSIGN TO ddname for base cluster RECORD KEY IS... ALTERNATE RECORD KEY IS..

Q47) Using Alternate Indexes in CICS pgms:Q47) 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.

Q48) What happens when you open an empty VSAM file in a COBOL program for input?Q48) 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.

Q49) How do you initialize a VSAM file before any operation? a VSAM with alternate index?Q49) Can write a dummy program that just opens the file for output and then closes it.

Q50) What does a file status of 02 on a VSAM indicate?Q50) Duplicate alternate key . Happens on both input and output operation