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VSAM

Version - 2.0
20th June 2000

1
VSAM

Day-wise Schedule .............................................................................................................. 4

1. INTRODUCTION TO VSAM ......................................................................................... 5

Features of VSAM............................................................................................................... 5

Advantages of VSAM ......................................................................................................... 5

Types of VSAM Datasets .................................................................................................... 5

VSAM history ..................................................................................................................... 6

2. VSAM Catalogs ................................................................................................................. 7

Vsam catalog ....................................................................................................................... 7

3. Inside VSAM Datasets ...................................................................................................... 9

Control Interval ................................................................................................................... 9

Spanned Records ............................................................................................................... 10

ESDS ................................................................................................................................. 10

KSDS ................................................................................................................................. 10

KSDS Structure ................................................................................................................. 11

4. IDCAMS COMMANDS ................................................................................................. 16

Format of IDCAMS command .......................................................................................... 17

IDCAMS return codes ....................................................................................................... 17

Defining an ESDS Cluster ................................................................................................. 19

5. LISTCAT ......................................................................................................................... 25

6. Creating Alternate Indexes............................................................................................. 27

Building Alternate Indexes ................................................................................................ 29

7. Reorganizing VSAM datasets......................................................................................... 31

With REPRO you can do the following ............................................................................ 31

Redefine the cluster using IDCAMS DEFINE CLUSTER command .............................. 33

8. VERIFY , PRINT, DELETE, ALTER Command ....................................................... 36

2
VSAM

VERIFY ............................................................................................................................ 36

DELETE ............................................................................................................................ 36

PRINT ............................................................................................................................... 37

ALTER .............................................................................................................................. 37

9. Generation DataSets........................................................................................................ 41

Physical deletion of entry .................................................................................................. 43

10. COBOL VSAM Considerations ..................................................................................... 46

11. Appendix-A ...................................................................................................................... 50

VSAM ASSIGNMENT ..................................................................................................... 50

12. Appendix -B ..................................................................................................................... 52

References ......................................................................................................................... 52

13. Appendix-C ...................................................................................................................... 53

Table of contents – Figures ......... Error! Bookmark not defined.Error! Bookmark not
defined.

14. Appendix-D ...................................................................................................................... 54

Table of contents – JCL Programs ..... Error! Bookmark not defined.Error! Bookmark
not defined.

3
VSAM

Day-wise Schedule
Day-1
What is catalog?
Types of VSAM datasets
IDCAMS command
COBOL Considerations for ESDS
Listcat overview

Day-2
Introduction to Alternate index
Define Aix
Define path
BLDIndex
COBOL Considerations for AIX

Day-3
IDCAM commands
REPRO, EXPORT/IMPORT
VERIFY, ALTER, DELETE
Additional options on
IDCAMS command
KEYRANGES, IMBED,
REPLICATE

Day-4
READPW, MASTERPW, UPDATEPW options
Creating and using Generation Dataset Groups
Deleting and altering GDGs

4
VSAM

1. INTRODUCTION TO VSAM
VSAM stands for Virtual Storage Access Method, is IBM high performance access method which
allows you to access files of different organization such as sequential, indexed, relative record and
linear datasets.

Features of VSAM
VSAM is one coherent file storage system used to store and retrieve data. It is not a database
management system like IDMS or DB2. It does not provide for relationships among the data. The
existing databases like IMS or DB2 may be implemented using VSAM.

VSAM is not a programming language. But you can access VSAM dataset through programming
languages like COBOL or PL/I. It is not a communication system like VTAM or CICS. It has no
equivalent for a ‘PDS’ type of file organization.

Advantages of VSAM
Provides protection of Data against unauthorized access through password facility.

Cross-system(MVS & VSE) Compatibility. VSAM datasets can be imported and imported in MVS
and VSE systems.

Device Independence (Access Via Catalog). The application programmer need not be concerned with
Block size ,volume and other control information, as access to VSAM dataset it always through the
Catalog and all control information are stored in the catalog entry of the dataset.

IDCAMS commands can be included in JCL to handle VSAM datasets

Types of VSAM Datasets
Clusters

VSAM files are often called clusters. A cluster is the set of catalog entries that represent a file. A
cluster consists of one or two components. All VSAM datasets consist of a data component in which
data records are placed . For KSDS , there is an additional index component, which contains the
indexes used to access records in the data component. ESDS RRDS and LDS have data component
only and no index component

VSAM clusters are categorized into 4 types based on the way we store and access the records:

ESDS Entry Sequenced dataset.

`These are sequential datasets that can be read in the sequence in which they were created. Records
can be added only to the end of the dataset.

5
VSAM

KSDS Key Sequenced dataset.

These datasets are stored in sequence of some key field in the record. The data component and index
component are separated. The keys are stored in a separate index and records are accessed through the
index. Individual records can be accessed randomly on the basis of the record key. Locating the
record is a two stage process.

 First search for the key in the index
 Use the information in the index to locate the record.

RRDS Relative record dataset.

These datasets associate a number to each record. There is no key field but records are accessed by
deriving the relative position of the record in the dataset.

LDS Linear dataset. These datasets consist of a stream of bytes which are accessed and written as
4k blocks accessed by Relative Byte Address

VSAM history
VSAM was introduced in 1973. This version had only Entry Sequence Datasets and Key Sequenced
Datasets. In 1975 Relative Record Datasets and alternate indexes for KSDS was added. In 1979
DF/EF VSAM was introduced with Integrated Catalog Facility (ICF).

DFP/VSAM Ver 1 was introduced in 1987 to run under the MVS/XA architecture. DFP/VSAM
version 2 introduced Linear Datasets (LDS)

DFP/VSAM version 3 was introduced to run under MVS/ESA architecture.
In 1991 version 3.3 supported variable-length records for RRDS.

6
VSAM

2. VSAM Catalogs
VSAM is totally catalog-driven. Catalogs are special purpose files residing on DASD (Direct Access
Storage Device) serving as a central repository for information about all datasets under its control.

There are two types of catalogs used
 Master catalog
 User catalog
There’s only one Master catalog per system. The entries in the master catalog may point to VSAM or
non-VSAM dataset, user catalogs, system datasets or other objects.
User catalogs contain same type of information as master catalog. All user catalogs must be cataloged
into master catalog.

Access to a dataset can only be made through a master or user catalog. Therefore all VSAM datasets
have to be cataloged. Non-VSAM datasets can also be cataloged. Catalogs are protected by RACF.

MASTER CATALOG

USER USER USER USER
CATALOG CATALOG CATALOG CATALOG

Figure 2.1 VSAM Catalog

Vsam catalog
Catalogs maintain the following information

 Name and physical location of datasets
 password information required to access protected datasets
 Statistics about datasets Example No. of records added, read, deleted or no. of Control
Interval/Control Area splits
 Information about dataset itself Example ESDS, KSDS, RRDS, CSIZE, KEYLENGTH
 Location of catalog recovery area

Vsam records
VSAM records can be fixed or variable length. Records can also be spanned

Vsam space allocation
VSAM space allocation depends on whether the dataset is cataloged in an ICF or the older VSAM
type catalog. For VSAM datasets cataloged in the newer ICF-type catalogs, dedicated space is
allocated dynamically when the cluster is created with the DEFINE CLUSTER command

7
VSAM

Each VSAM dataset cataloged in an ICF catalog has its own VTOC entry. These VSAM datasets can
have 1 primary and 122 secondary allocation unlike OS dataset which can have only 1 primary and 15
secondary extends on a volume.

Vsam space management

VSAM maintains detailed information in its catalogs about DASD space allocated to VSAM files.
This allocation information stored in the catalog is more comprehensive and flexible than the
equivalent information stored for a non-VSAM file in VTOC.

Sub Allocation

Once the space has been allocated, VSAM has complete control over subsequent allocations within
that space. Within that space, VSAM can create suballocated files. Whenever a suballocated files need
to be created, extended or deleted, VSAM uses it own space management facilities.

Unique Allocation
Alternatively an entire VSAM space can be allocated to single VSAM file. In that case allocation for
the file called UNIQUE file, is managed by DADSM rather than by VSAM. Allocation information
for the unique files is maintained in two places : the VSAM catalog entry for the file and the VTOC
entry for the space that contains unique file.

The figure below shows two DASD volumes. The first volume has a VSAM dataspace contains two
sub-allocated files. Notice that there’s unused space within the dataspace too. However, that space is
not available to non-VSAM files because it’s already under VSAM’s control. The second DASD
volume contains two unique VSAM datasets. All of the unused space on the volume is available to
both VSAM and Non-VSAM datasets. Under VSE/VSAM & OS/VS VSAM most VSAM datasets are
sub-allocated. Under ICF, there is no VSAM space. All VSAM files are Unique

VOLUME 1 VOLUME II

Non-VSAM Non-VSAM

File I VSAM File III unique
datasets
VSAM
under
file
Available Space VSAM’s Non-VSAM
control

File II File IV

Non-VSAM
Available Space

Non-VSAM

Figure 2.2 Space Allocation

8
VSAM

3. Inside VSAM Datasets

Control Interval
A control interval is the unit of data VSAM transfers between virtual and disk storage. It is similar to
the concept of blocking in non-VSAM files. Each control interval can contain more than one logical
record.

The size of CI must be between 512 bytes to 32K. Upto 8K bytes it must be multiple of 512, beyond
this it is multiple of 2K. The length of the CI is specified at file creation time.

For index component, the size of CI is 512, 1K, 2K or 4K bytes.

A Control Inverval consists of records, free space and control field information as shown below

Rec1 Rec2 Rec3 Free Space Unused Space Control Field

Figure 3.1 Contents of Control Interval

In the Control Interval shown above Rec1, Rec2, Rec3 are records. Free Space is where new records
can be inserted.

RDF CIDF

Figure 3.2 Contents of Control Field

Control Interval Descriptor Field(CIDF) contains information about available space within CI. Record
Descriptor Field (RDF) contains the length of each record and how many adjacent records are of the
same length. There’s one RDF for each record in variable length records.
There will be only two RDFs per CI in case of fixed length files. One RDF specifies the length of the
record and the second RDF specifies how many records are there in the CI. Each RDF is of 3 bytes .

9
VSAM

VSAM groups control intervals into contiguous, fixed length areas of storage called Control Areas.
Maximum size of a CA is 1 cylinder. You can also specify freespace in CA. The total number of
CI/CA in a Cluster is determined by VSAM.

CONTROL AREA

CONTROL INTERVAL
CONTROL INTERVAL
CONTROL INTERVAL
CONTROL INTERVAL
CONTROL INTERVAL

Figure 3.3 Control Area

Spanned Records
Spanned records are records larger than the specified CI size. That is they span more than one CI. So
one spanned record may be stored in several CIs. Each CI that contains a record segment of a spanned
record has two RDFs. The right RDF gives the length of the segment and the left gives the update
number of the segment. Spanned records can exist only in ESDS and KSDS.

A CI that contains a record segment of a spanned record contains no other data. Records can span
Control Intervals but not Control Areas. For KSDS the entire key field of the spanned record must be
in the first Control Interval.

Logical Record 1

Record1 RC Record1 RC Record1 RC
Segment2 Segment3
Segment1

Figure 3.4 Spanned Record

ESDS
ESDS is a sequential dataset. Records are retrieved in the order in which they are written to the
dataset. Additions are made always at the end of the file. Records can be retrieved randomly by using
RBA(Relative Byte Address). RBA is an indication of how far, in bytes, each record is displaced from
the beginning of the file.

KSDS
In Key Sequenced Datasets logical records are placed in the dataset in the ascending collating
sequence by the key field.

10
VSAM

Rules for key

 Key must be unique in a record

 Key must be in same position in each record and key data must be contiguous

 When a new record is added to a dataset it is inserted in its collating sequence by key

A KSDS consists of two components index component and data component
DATA Component :- Contains control areas which in turn contains Control Intervals as shown in
Figure 3.5

Control Areas



Data Component Control Intervals

Figure 3.5 Contents of Control Area
KSDS Structure

Index Set

Sequence Set

Figure 3.6 Contents of KSDS Index

11
VSAM

The first level of index is called a Sequence set. The Sequence set consists of Primary keys and
pointers to the Control Intervals holding records with these primary keys. The Sequence set is always
in sequential order of the primary keys. The Control Intervals may be in any order. VSAM uses the
Sequence Set to access records in the KSDS sequentially.

The index component is a separate entity with a different CI size , a different name and can be stored
on a different volume.

Control interval splits can occur in Indexes also

Sequence Set

Key Ptr Key Ptr Key Ptr Key Ptr

CI CI CI CI

Figure 3.7 Contents of Sequence Set

Index Set

Index
component
Sequence Set Sequence Set

CI CI CI CI CI CI CI CI
CA1 CA2

Figure 3.7 Contents of Index Set

12
VSAM

New
Record

Record1 Record2 Record3 FSPC US CF

After Inserting

Record1 Record2 New Record Record 3 FSPC US CF

Figure 3.8 Inserting a new record into a KSDS

Before Control Interval Split

New
Record Full
Control Interval

Rec1 Rec2 Rec3 Rec4 Rec5 US CF

FSPC US CF

Empty
Control
Interval

Figure 3.9 Inserting a new record into a full CI

13
VSAM

Record1 Record2 New Record FSPC US CF

Record3 Record4 Record5 FSPC US CF

Figure 3.10 After Control Interval Split

Sequence Set

I 0 K 100

New
Record

RecordA RecordB RecordF RecordG FSPC US CF

100

RecordJ RecordK FSPC US CF

200

FSPC US CF

Figure 3.11a Effect of Control Interval Split on Sequence Set

14
VSAM

E 0 I 200 K 100

0
RecordA RecordB RecordC FSPC US CF

100
RecordJ RecordK FSPC US CF

200

RecordF RecordG FSPC US CF

Figure 3.11b Effect of Control Interval split on Sequence Set

15
VSAM

4. IDCAMS COMMANDS


You can write IDCAMS utility program

1. To create VSAM dataset

2. To list, examine, print, tune, backup, and export/import VSAM datasets.

The IDCAMS utility can be invoked in batch mode with JCL or interactively with TSO commands.
With JCL you can print/display datasets and system messages and return codes. Multiple commands
can be coded per job. You can use IF-THEN-ELSE statement to execute command/s selectively based
on condition codes returned by previous commands.
Listed below are the IDCAMS commands to be discussed in this course

 DEFINE

 MODAL COMMANDS

 IF

 SET

 PARM

 BUILDINDEX

 REPRO

 PRINT

 DELETE

 VERIFY

 IMPORT/EXPORT

 ALTER

 LISTCAT

The example 4.1 shown below is a skeleton JCL for executing IDCAMS commands. The PGM
parameter specifies that the program to be executed is IDCAMS utility program . The statements that
follow SYSIN DD * are IDCAMS commands. The end of data is specified by /*.

Optionally JOBCAT and STEPCAT statements may be coded to indicate catalog names for a job/step,
in which concerned dataset may be cataloged
// jobname JOB (parameters)
// stepname EXEC PGM=IDCAMS
// SYSPRINT DD SYSOUT = *
[// ddname DD DSN=datasetname,
DISP= SHR/ OLD
]

16
VSAM

//SYSIN DD *
IDCAMS command/s coded freely between 2 to 72 cols.
/*
//
Optionally:
// JOBCAT DD DSN = catalogname, DISP= SHR
// STEPCAT DD DSN = catalogname, DISP = SHR

Example 4.1 JCL for executing IDCAMS commands

Format of IDCAMS command
verb object (parameters)

Every IDCAMS command starts with a verb followed by object which takes some parameters. In the
code listing 4.2 DEFINE is the verb CLUSTER is the object which takes a dataset
DA0001T.LIB.KSDS.CLUSTER as parameter

DEFINE CLUSTER -
NAME(DA0001T.LIB.KSDS.CLUSTER) -
CYLINDERS(5, 1) -
VOLUMES (BS3013) -
INDEXED -
)

Example 4.2 Creating a cluster

Comments:
Comments in IDCAMS can be specified in the following manner

/* comment */
or
/* -----
*/

IDCAMS return codes
The IDCAMS Commands return certain codes which have the following interpretation

Condition code:

0 : command executed with no errors
4 : warning - execution may go successful
8 : serious error - execution may fail
12 : serious error - execution impossible
16 : fatal error - job step terminates

The condition codes are stored in LASTCC/MAXCC. LASTCC stores the condition code for
the previous command and MAXCC stores the maximum code returned by all previous

17
VSAM

commands. Both LASTCC and MAXCC contain zero by default at the start of IDCAMS
execution. You can check the condition code of the previous command and direct the flow of
execution or terminate the JCL.

Syntax of IF statement

IF LASTCC/MAXCC
comparand VALUE -
THEN -
command
ELSE
Command

Comparand(s) are: EQ/NE/GT/LT/GE/LE

Hyphen is required after then to indicate the continuation of the command on the next line . Comment
is assumed as null command. ELSE is optional. LASTCC and MAXCC values can be changed using
the SET command.

Note: LASTCC and MAXCC can also be set to any value between 0-16

e.g. SET LASTCC = 4
Setting MAXCC has no effect on LASTCC. Setting LASTCC changes the value of MAXCC, if
LASTCC is set to a value larger than MAXCC. Setting MAXCC = 16 terminates the job
.........
REPRO INFILE (INDD) -
OUTFILE (OUTDD)
................
IF LASTCC EQ 0 -
THEN -
PRINT OUTFILE (INDD)
ELSE
PRINT INFILE (OUTDD)
IF MAXCC LT 4 -
THEN -
DO
/* COMMENT */
Command
Command
END
ELSE
Command

Example 4.3a JCL using MAXCC and LASTCC

DEFINE CLUSTER
….
IF LASTCC > 0 THEN
SET MAXCC = 16
ELSE
REPRO
……

Example 4.3b JCL using MAXCC and LASTCC

18
VSAM

Defining an ESDS Cluster
DEFINE CLUSTER

Clusters are created and named with the DEFINE CLUSTER command.

The NAME parameter
This is a required positional parameter.

Format: NAME(Cluster-Name)
Cluster name:- The name to be assigned to the cluster

Example: NAME(DA0004T.LIB.KSDS.CLUSTER)
The cluster Name becomes the dataset name in any JCL that invokes this cluster either as an input or
output

//INPUT DD DSN=DA0004T.LIB.KSDS.CLUSTER,DISP=SHR

The high-level qualifier is important because in most installations this technique ensures that VSAM
datasets are cataloged in the appropriate user catalog.

Rules for Naming Cluster

Can have 1 to 44 alphanumeric characters

Can include the national characters #, @, $

Segmented into level of eight or fewer characters, separated by periods

The first character must be either alphabetic or national character

The SPACE Allocation parameter

The space allocation parameter specifies space allocation values in the units shown below:

Format :
CYLINDERS(Pri Sec)
TRACKS(Pri Sec)
RECORDS(Pri Sec)
KILOBYTES(Pri Sec)
MEGABYTES(Pri Sec)

Primary: Number of units of primary space to allocate. This amount is allocated once when the dataset
is created

Secondary: Number of units of secondary space to allocate. This amount is allocated a maximum of
122 times as needed during the life of the dataset. VSAM calculates the control area size for you. A
control area size of one cylinder usually yields best performance. To ensure control area size of one
cylinder you must allocate space in CYLINDERS.

19
VSAM

Allocating space in RECORDS must be avoided as this might result in an inefficient Control Area
size.

The VOLUMES parameter

This VOLUMES parameter assigns one or more storage volumes to your dataset. Multiple
volumes must be of the same device type.

Format:
VOLUMES(volser) or VOLUMES(volser ........ volser)

volser: The 6 digit volume serial number of a volume.

Example:
VOLUMES(BS3011)
VOLUMES(BS3011 BS3040 BS3042)

You can store the data and index (in case of KSDS clusters) on separate volumes as this may
provide a performance advantage for large dataset

The Recordsize parameter

This parameter tells VSAM what size records to expect. The avg and max are average and
maximum values for variable length record. If records are of fixed length, avg and max should be the
same.

Format:

RECORDSIZE(avg max)

avg: Average length of records
max: Maximum length of records
e.g. :
RECORDSIZE(80 80) [Fixed Length records]
RECORDSIZE(80 120) [Variable Length records]
RECORDSIZE can be assigned at the cluster or data
level

Note :

This is an optional parameter, if omitted default is RECORDSIZE(4086 4086)

The SPANNED parameter

This parameter allows large record to span more than one control interval. However records cannot
span Control Areas. The resulting free space in the spanned control interval is unusable by other
records, even if they fit logically in the unused bytes. [NONSPANNED is the default] & it means that
records cannot span control intervals

The DATASET-TYPE parameter

This parameter specifies whether the dataset is INDEXED(KSDS),

20
VSAM

NONINDEXED(ESDS), or NUMBERED(RRDS).

Format : INDEXED| NONINDEXED | NUMBERED

INDEXED:- Specifies a KSDS and is the default
NONINDEXED:- Specifies an ESDS. No index is created and records are accessed
sequentially or by relative byte address
NUMBERED:- Specifies an RRDS
LINEAR:- Specifies a LINEAR dataset

The default dataset Type is INDEXED.

//DA0001TA JOB LA2719, PCS,MSGLEVEL=(1,1),
// MGCLASS=A,NOTIFY=DA0001T
// * Delete/Define Cluster for ESDS VSAM Dataset
//STEP1 EXEC PGM=IDCAMS
// SYSPRINT DD SYSOUT = *
// SYSIN DD *
DELETE DA0001T.LIB.ESDS.CLUSTER

DEFINE CLUSTER -
(NAME(DA0001T.LIB.ESDS.CLUSTER) -
NONINDEXED -
RECORDSIZE(125 125) -
RECORDS(100 10) -
NONSPANNED -
VOLUMES (BS3013) -
REUSE - ) -
DATA(NAME(DA0001T.LIB.ESDS.DATA))

Example 4.4 JCL for Defining an ESDS Cluster

Defining KSDS Cluster
While defining a KSDS Cluster it is essential to code the DATA, INDEX and KEYS parameter

The DATA parameter

The DATA parameter tells IDCAMS that you are going to create a separate data component. This
parameter is optional for ESDS and RRDS datasets. You should code the NAME parameter of
DATA for KSDS datasets, in order to operate on the data component by itself.

Format : DATA(NAME(dataname) Parameters)

dataname :- The name you choose to name the data component

The INDEX parameter
The INDEX parameter creates a separate index component

Format :
INDEX(NAME(indexname) Parameters)
indexname : The name you choose to name the index component

21
VSAM

INDEX(NAME(DA0004T.LIB.KSDS.INDEX))

When you code the DATA and INDEX parameters, you usually coda a NAME parameter for them. If
you omit the NAME parameter for DATA and INDEX , VSAM appends .DATA or .INDEX as the
low-level qualifier.

The KEYS parameter

This parameter defines the length and offset of the primary key in a KSDS record.
The offset is the primary key’s displacement (in bytes) from the beginning of the record.

Format :
KEYS(length offset)

length : length in bytes of the primary key
offset : Offset in bytes of the primary key with records (0 to n)

Example :
KEYS(8 0)
VSAM records begin in position zero

Note :
Default is KEYS(64 1) [Key is in bytes 2 thru 65]

//DA0001TA JOB LA2719, PCS,MSGLEVEL=(1,1),
// MGCLASS=A,NOTIFY=DA0001T
// * Delete/Define Cluster for KSDS VSAM Dataset
//*
//STEP1 EXEC PGM=IDCAMS
// SYSPRINT DD SYSOUT=*
// SYSIN DD *
DELETEDA0001T.LIB.KSDS.CLUSTER
DEFINE CLUSTER(
NAME(DA0001T.LIB.KSDS.CLUSTER) -
INDEXED -
KEYS(4 0) -
FSPC(10 20) -
RECORDSIZE(125 125) -
RECORDS(100 10) -
NONSPANNED -
VOLUMES (BS3013) -
NOREUSE - )-
DATA(NAME(DA0001T.LIB.KSDS.DATA)) INDEX(NAME(DA0001T.LIB.KSDS.INDEX))
/*
//

Example 4.5 JCL for Defining a KSDS Cluster

The FREESPACE parameter

This FREESPACE parameter, which applies to the KSDS, allocates some percentage of control
interval and control area for planned free space. This free space can be used for adding new records or
for expanding existing variable records. FREESPACE applies only to the data component

Format :
FREESPACE(%CI %CA)

22
VSAM

%CI :- Percentage of control interval to leave free for expansion
%CA :- Percentage of control area to leave free for expansion

Example : FREESPACE(20 10)
Too much free space results in more i/o, especially when doing sequential processing. Too
little results in excessive control interval and control area split

Note :
Default is FREESPACE(0 0)

The REUSE parameter

The REUSE parameter specifies that the cluster can be opened a second time as a reusable
cluster. NOREUSE is the default, and specifies the cluster as non-reusable.

Format :

REUSE|NOREUSE

Some application call for temporary dataset or workfile that must be created, used and deleted each
time the application runs. To simplify these applications, VSAM lets you create reusable files. The
reusable file is a standard VSAM KSDS, ESDS or RRDS. The only difference is that, if you open an
existing reusable file for output processing, VSAM treats the file as if were empty. Any records
already present in the file are ignored.

The CONTROL INTERVAL SIZE parameter

This parameter specifies the Control Interval size. It is usually abbreviated CISZ.

Format :
CISZ(bytes)

Example :
CISZ(4096)

Note : If omitted VSAM calculates CISZ based on record size.

Remark : Control Interval is VSAM’s equivalent of a block and it is the unit of data that is actually
transmitted when records are read or written.

Guidelines for determining the CISZ

ESDS is processed sequentially, so the CISZ should be relatively large, depending on the size of the
record. For sequential processing with larger records you may choose a CISZ of 8k

For datasets processed randomly as well as sequentially (for backup at night) choose a CISZ for
random processing and then allocate extra buffers for sequential processing with the AMP JCL
parameter.

RRDS is usually processed randomly, so the CISZ should be relatively small, depending on the size
of the record.

23
VSAM

SHAREOPTIONS
This parameter tells VSAM whether you want to let two or more jobs to process your file at the same
time. It specifies how a VSAM dataset can be shared

Format :

SHARE OPTIONS(cr value cs value)

cr value : Specifies the value for cross region sharing. Cross region sharing is defined as different
jobs running on the same system using Global Resource Serialization(GRS), a resource control
facility available only under MVS/XA and ESA
cs value : Specifies the value for cross system sharing means different jobs running on different
system in a NONGRS environment

Values :-
 multiple read OR single write
 multiple read AND single write
 multiple read AND multiple write

Default :- SHAREOPTIONS(1 3)

24
VSAM

5. LISTCAT
LISTCAT’s basic function is to list information about VSAM and NONVSAM objects. With
LISTCAT you can also view password and security information, usage statistics, space allocation
information, creation and expiration dates etc.

Format 1:

LISTCAT ENTRIES(entryname) options

Options are :
 HISTORY
 VOLUME
 ALLOCATION
 ALL

ENTRIES (ENT) requires you to specify each level of qualification, either explicitly or implicitly,
using an asterisk as a wild card character.

Examples:

LISTCAT
ENT(DA0001T.VSAM.KSDS.CLUSTER) -
CLUSTER -
ALL -

Example 5.1 LISTCAT

The above command will only display the base cluster

LISTCAT
ENT(DA0001T.VSAM.KSDS.CLUSTER) -
DATA -
ALL -

The above command will only display the data component

LISTCAT
ENT(DA0001T.VSAM.KSDS.CLUSTER) -
ALL

The above command will display all catalog information.
//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
LISTCAT -
ENTRIES(DA0001T.LIB.KSDS.CLUSTER) ALL
/*

25
VSAM

Format 2:

LISTCAT LEVEL(level) options
LEVEL by definition lists all lower levels. VSAM assumes that qualifier to be the high-level qualifier
and list every entry with that high level qualifier .

Example
LISTCAT LVL(DA0001T.*.KSDS) ALL

The above will list all entries with DA0001T as high level qualifier, anything in the second-level
qualifier and KSDS in the third-level qualifier. That is it would list DA0001T.ABC.KSDS and
DA0001T.TEST.KSDS.AIX, DA0001T.TEST.KSDS.DATA.

To execute LISTCAT from TSO prompt

LISTCAT ENTRIES (LIB.KSDS.CLUSTER) ALL

If you analyze the output of the LISTCAT command there is ALLOCATION information which
shows two fields HURBA and HARBA.

High-Used-RBA (HURBA) points to the end of the data. High-Allocated-RBA (HARBA)is the
highest byte that can be used.

HIGH-ALLOC-RBA indicates the Relative Byte Address (plus 1) of the last allocated data control
area. This value reflects the total space allocation for the data component.
HIGH-USED-RBA indicates the Relative Byte Address (plus 1) of the last used data control area.
This value reflects the portion of the space allocation that is actually filled with data records.

There are actually to HURBAs one in the VSAM control block of the cluster and one in the catalog
entry for the cluster.
You can write application programs (in COBOL, PL/I Assembler Language, in CICS) and use the
statements provided by these languages to write and read VSAM datasets

VSAM cluster
HARBA
Data space
allocated but
empty

HURBA

Data space
loaded with
records

Figure 5.1 HURBA and HARBA

26
VSAM

6. Creating Alternate Indexes
An Alternate Index AIX provides a view of data different from the one offered by the primary key.
For example for a KSDS dataset Employee, you may have a Record Key index on Employee-no and
an Alternate Index on Employee-Name. You can now browse and even update the same KSDS in
logical sequence by Employee-Name.

Alternate Indexes may be defined on one or more than one Alternate Key(s) i.e. Field(s) other than
primary key. Alternate Key(s) need not be unique. Each alternate index itself is a KSDS with data and
index component.

Alternate Index greatly reduces redundancy. There is no need to keep a separate dataset for different
views like Employees’ Social Security No. The records may be accessed sequentially or randomly
based on the alternate record keys.

They can be updated automatically when the base cluster is updated.

Alternate Indexes do not support a reusable base cluster. So NOREUSE which is the default, should
be specified.

Too many Alternate Indexes built on a KSDS may lead to performance Degradation as access by
alternate key requires twice as many I/O’s. VSAM first locates the primary key from the alternate
index and then locates the Control Interval information from the record key index.

For ESDS, VSAM builds AIX by mapping one field to the record’s RBA.

Steps for defining and building alternate indexes:
DEFINE AIX Command
Define the Alternate Index Cluster using the IDCAMS DEFINE AIX command.
//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT =*
//SYSIN DD *
DEFINE AIX -
(NAME(DA0001T.LIB.KSDS.AUTHNAME.AIX)
-
VOLUMES (BS3013) -
RELATE(DA0001T.LIB.KSDS.CLUSTER)
-
UPGRADE -
TRACKS(10 1)
-
KEYS(25 9) -
RECORDSIZE(70 110)
FREESPACE(20 10)
-
SHAREOPTIONS(1) -
NONUNIQUEKEY) -
)
DATA(NAME(DA000A1T.LIB.KSDS.AUTHNAME.DATA)) -
INDEX(NAME(DA0001T.LIB.KSDS.AUTHNAME.INDEX)
/*
//

27
VSAM

Example 6.1 JCL to define AIX

Pathname is the dataset name in JCL (DSN=PATHNAME)

RELATE Parameter

Format:
RELATE(base cluster name)

This parameter establishes the relationship between the base cluster and the alternate index via the use
of the base cluster name. It is unique to the DEFINE AIX command, and it is required.

The RECORDSIZE Parameter

Format:
RECORDSIZE(avg max)

This parameter specifies the average and maximum length of each alternate index record. There are
two types of alternate indexes.

KSDS unique alternate index: You can create a unique alternate index by specifying the
UNIQUEKEY parameter. The records of unique alternate indexes are of fixed length. The length of a
unique alternate index built over a KSDS is derived as follows:

HOUSEKEEPING Soc-Sec-No Emp-No
5 9 8

Figure 6.1 Contents of KSDS unique alternate index

For example if an unique alternate index on Soc-Sec-No is built on our KSDS cluster Employee then
the RECORDSIZE will be calculated as follows:-

5 Bytes fro HouseKeeping + size of alternate key + Size of Primary Key that the alternate

= 5 + 9 + 8 = 22

Therefore recordsize parameter will be coded as RECORDSIZE(20 20)

KSDS non-unique alternate index: An alternate index created with a NONUNIQUEKEY parameter
has variable length records. The RECORDSIZE is calculated as follows:-

Average Record length = 5 bytes for House Keeping + size of the alternate key + size of the
primary key x average no of records the alternate index key can point to

Maximum Record length = 5 bytes for House Keeping + size of the alternate key + size of the
primary key x maximum no of records the alternate index key can point to

28
VSAM

DEFINE PATH Command:

Define an Alternate Index Path using the IDCAMS DEFINE PATH command. The path forms a
connection between the alternate index and the base cluster. Path name becomes a catalog entry but
path does not contain any records. The path name is specified in the JCL for applications that access
records via the alternate index.

//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT =*
//SYSIN DD *
DEFINE PATH -
NAME(DA0001T.LIB.KSDS.AUTHNAME.PATH) -
PATHENTRY(DA0001T.LIB.KSDS.AUTHNAME.AIX) -
UPDATE -
)
/*
//

Example 6.2 JCL to define PATH for the AIX

UPDATE vs NOUPDATE

Records may be accessed by applications by the alternate index path alone, without opening the base
cluster. In such cases any changes made to data will be reflected in the alternate index records if the
UPDATE option is specified. If NOUPDATE is specified then the alternate index records will not be
automatically updated.

UPGRADE vs. NOUPGRADE

The UPDATE/NOUPDATE option of DEFINE PATH works in tandem with the UPGRADE /
NOUPGRADE of the DEFINE AIX command.

UPGRADE specifies that any changes made in the base cluster records will be reflected immediately
in the alternate index records if the base cluster is opened in the application. Fortunately UPGRADE
and UPDATE are defaults for their respective commands.

Building Alternate Indexes
The final step in creating an alternate index is to actually build and populate it with records.
The BLDINDEX command does the following:

 The data component of the base cluster is read sequentially and pairs of key pointers are
extracted. These pairs consist of the alternate key field and its corresponding primary key
field. VSAM creates a temporary file with these records.

 This temporary file is sorted in ascending alternate key sequence.

 If NONUNIQUEKEY option is specified then a merge operation takes place, which will
merge all records with the same alternate key into a single record.

29
VSAM

 These records are the data component of the Alternate Index. VSAM now constructs the
index component just as it does for the KSDS.

Note: The Alternate Index can be built only after the base cluster has been both defined and loaded with atleast
1 record.

//STEP1 EXEC PG=IDCAMS
//SYSPRINT DD SYSOUT =*
//DD1 DD DSN=DA0001T.LIB.KSDS.CLUSTER,
// DISP=OLD
//IDCUT1 DD UNIT=SYSDA,SPACE=(TRK, (2, 1))
//IDCUT2 DD UNIT=SYSDA,SPACE=(TRK, (2, 1))
// SYSIN DD *
BLDINDEX -
INFILE(DD1) -
OUTDATASET(DA0001T.LIB.KSDS.AUTHNAME.AIX) -
INTERNALSORT
/*
//
Example 6.3 JCL to build Alternate Index

Disposition of base cluster is DISP=OLD as the BLDINDEX needs absolute control of the base
cluster. Output dataset can be Alternate index cluster or pathname

The INTERNALSORT uses virtual storage whereas EXTERNAL SORT uses disk space.
INTERNALSORT is the default. If you want an external sort to be performed then include IDCUT1
and IDCUT2 DD statements in your JCL and specify EXTERNALSORT in the BLDINDEX
command.

DEFINE Cluster
(NAME(DA0001T.LIB.KSDS.CLUSTER)
.
)
DEFINE AIX
(NAME(DA0001T.LIB.KSDS.AUTHNAME.AIX) RELATE(DA0001T.LIB.KSDS.CLUSTER)
.
)
DEFINE PATH (NAME(DA0001T.LIB.KSDSK.AUTHNAME.PATH)
PATHENTRY(DA0001T.LIB.KSDS.AUTHNAME.AIX)
.
)
BLDINDEX
INDATASET(DA0001T.LIB.KSDS.CLUSTER) OUTDATASET(DA0001T.LIB.KSDS.AUTHNAME.AIX)
.
)

Example 6.4 Steps for creating and building AIX

30
VSAM

7. Reorganizing VSAM datasets
This chapter explains the commands used to back up and restore existing datasets, protect the integrity
of data.

REPRO

This command is used to:

 Loads empty VSAM cluster with records.
 Creates backup of a dataset
 Merge data from two VSAM datasets

REPRO command can operate on non-VSAM datasets. It is an all-purpose load and backup utility
command and can be used in place of IEBGENER.

With REPRO you can do the following
 Convert an ISAM dataset to VSAM format
 Copy a non-VSAM dataset to a physical sequential or partitioned dataset
 Copy record from one type of VSAM datasets to another. For example KSDS to ESDS

REPRO has following disadvantages:
 Little control over the input data
 Catalog information is not copied with the data
 Prior DELETE and redefinition is required before loading the cluster unless you have
specified REUSE in the DEFINE CLUSTER command

Incase of KSDS, data and index component are build automatically.

REPRO Command Syntax
Format :
REPRO
INFILE(ddname) | INDATASET(dsname) -
OUTFILE(ddname) | OUTDATASET(dsname) -

Optional parameters are :
FROMKEY FROMADDRESS
FROMNUMBER SKIP
TOKEY TOADDRESS
TONUMBER COUNT
INFILE and OUTFILE are required parameters that point to DD1(input file) and DD2 (output file)
respectively .

Limiting Input and Output Records:-

While it is not possible to edit the input to REPRO, you can limit the input by providing the optional
parameters.

31
VSAM

FROMKEY and TOKEY parameters: FROMKEY specifies the key of the input records at which
to begin reading. TOKEY specifies the key to stop reading or the last input record.

SKIP and COUNT parameters. SKIP specifies the number of input records to skip before beginning to
copy. COUNT specifies the number of output records to copy. You can specify both. For example
skip 10 records and copy next 10

//DD1 DD DSN=DA0001T.INPUT.KSDS,DISP=OLD
//DD2 DD DSN=DA0001T.OUTPUT.KSDS, DISP=OLD
//SYSIN DD *
REPRO -
INFILE(DD1) -
OUTFILE(DD2) -
FROMKEY(A001) -
TOKEY(A069)

Example 7.1 JCL for Loading Dataset:

Other parameter for filtering records:

FROMADDRESS (RBA)
TOADDRESS(RBA)
FROMNUMBER (RRN)
TONUMBER(RRN)
COUNT (NO.)
SKIP(NO)

Backing up VSAM Datasets

It is good to backup VSAM datasets on a regular basis.
REPRO command is used to rebuild and restore VSAM cluster from the backup copy.
Backing up a VSAM dataset involves only one step

//JOBNAME DA0001TA…
//STEP10 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT = *
//DD2 DD DSN=DA0001T.KSDS.INV.BACKUP(+1),
// DISP=(NEW,CATLG,DELETE),UNIT=TAPE,
// VOL=SER=32970,LABEL=(1,SL),
// DCB=(RECFM=FB,LRECL=80)
//SYSIN DD *
REPRO
INDATASET(DA0001T.KSDS.INV.CLUSTER) –
OUTFILE(DD2)
/*
//

Example 7.2 Using Repro for backup

In the example above INDATASET is the input file and DD2 is the output tape dataset which is a part
of the GDG while is more or less like a physical sequential file. (Ref to chapter 10 for more on GDG’s
)

32
VSAM

Restoring and rebuilding the backup

DELETE-DEFINE-REPRO sequence required to restore the cluster incase of KSDS.
Delete the original cluster using IDCAMS DELETE command
Redefine the cluster using IDCAMS DEFINE CLUSTER command
Load the empty cluster with data using the IDCAMS REPRO command

When you DELETE-DEFINE-REPRO a VSAM dataset it has the following effects on the KSDS.
 The dataset is reorganized that is the Control Interval and Control Area splits are eliminated
 Free space is redistributed throughout the dataset as specified in the FREESPACE parameter.
 Primary index is rebuilt, however the DELETE command deletes the base cluster as well as
its indexes. So the alternate indexes have to be redefined

ESDS or RRDS need not be reorganized because the record position is fixed permanently by sequence
of entry or record number.

//DD1 DD DSN=DA0001T.LIB.KSDS.BACKUP(0),
// DISP=OLD, UNIT=TAPE,LABEL=(1,SL)
//SYSIN DD *
DELETE DA0001T.LIB.KSDS.CLUSTER
/* DEFINE CLUSTER NAME(DA0001T.LIB.KSDS.CLUSTER) -
INDEXED -
KEYS(4 0) -
RECORDSIZE(80 80) -
VOLUMES(BS3013) -
) -
DATA(NAME(DA0001T.LIB.KSDS.DATA)) -
INDEX(NAME(DA0001T.LIB.KSDS.INDEX))
REPRO -
INFILE(DD1) -
OUTDATASET(DA0001T.LIB.KSDS.CLUSTER)
/*

Example 7.3 DELETE-DEFINE-REPRO

Merging datasets with REPRO

The REPRO command can also be used to merge two datasets into one. The target dataset can be a
nonempty KSDS, ESDS or RRDS. If the target dataset is an ESDS, the merged records are added to
the end of the existing dataset.

EXPORT/IMPORT Commands

The EXPORT/IMPORT commands can be used for backup and recovery . You can export a dataset,
alternate index or a catalog to a different system.

EMPORT/IMPORT has several advantages as compared to REPRO

Catalog information is exported along with data

Cluster deletion and redefinition not required during import as input dataset already contains catalog
information

33
VSAM

Easily ported on other systems as catalog information available with data

Like REPRO KSDS datasets are reorganized however three steps of REPRO are replaced by one

Disadvantages:

Exported data cannot be processed until Imported

Can be used only for VSAM dataset

EXPORT

FORMAT :

EXPORT entryname | password
OUTFILE(ddname) |
OUTDATASET(dsname)

Optional parameters

Example :

EXPORT DA0001T.LIB.KSDS.CLUSTER -
OUTFILE(DD2)

The output dataset from an EXPORT must always
be a sequential dataset (usually on a tape)

IMPORT
Format :

IMPORT -
INFILE(ddname) | INDATASET(dsname) -
OUTFILE(ddname) | OUTDATASET(dsname) -

Optional parameters:

IMPORT INFILE (DD2) -
OUTDATASET(DA0001T.LIB.KSDS.CLUSTER)

Imports only EXPORTED dataset

34
VSAM

//DA0001TA JOB LA1279,PCS,MSGLEVEL=(1,1),
// MSGCLASS=A, NOTIFY=DA0001T
//* Input instream Data into ESDS VSAM Dataset
// STEP1 EXEC PGM=IDCAMS
// SYSPRINT DD SYSOUT = *
// DD1 DD *
123456789123456789
AAAAAAAABBBBBBCCCC
/*
//DD2 DD DSN=DA0001T.ESDS.CLUSTER
//SYSIN DD *
REPRO -
INFILE(DD1) -
OUTFILE(DD2)
/*
//

Example 7.4 Input instream Data into ESDS

//DA0001TA JOB LA2719,PCS,MSGLEVEL= (1,1),
// MSGCLASS=A, NOTIFY=DA0001T
//* Load Data from a file into ESDS VSAM Dataset
//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT = *
//DD1 DD DSN=DA0001T.ESDS.CLUSTER1
//DD2 DD DSN=DA0001T.ESDS.CLUSTER2
//SYSIN DD *
REPRO -
INFILE(DD1 -
OUTFILE(DD2)
/*
//

Example 7.5 Load Data from a file into ESDS

35
VSAM

8. VERIFY, PRINT, DELETE, ALTER
Command
VERIFY
Verify - preserves data integrity (HURBA)

Format:
VERIFY FILE(ddname/passwd)
or
VERIFY DATASET(entryname/passwd)
VERIFY entryname/passwd (TSO)

VERIFY DATASET(DA0001T.LIB.KSDS.CLUSTER)

Example 8.1 VERIFY

Remark:

VERIFY can be issued from a TSO or within a JCL statement.
It is valid only for VSAM dataset except LDS.

DELETE
- logically deletes dataset
- catalog entry deleted

Format :
DELETE entryname/passwd -
optional parameters

DELETE DA0001T.LIB.KSDS.CLUSTER -
ERASE
Example 8.2 Deleting a Cluster

Optional parameters are:
 AIX
 CLUSTER
 NONVSAM
 PATH
 ERASE | NOERASE
 FORCE | NOFORCE
 PURGE | NOPURGE
 SCRATCH | NOSCRATCH

36
VSAM

//DA0001TA JOB LA2179,PCS,MSGLEVEL=(1, 1) ,
// NOTIFY=DA0001T
//* Deletes VSAM Dataset
//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT = *
//SYSIN DD *
DELETE DA0001T.TRAIN.ITMFOIV
/*
//

Example 8.3 Delete VSAM Dataset

PRINT
The default output destination for PRINT is SYSPRINT.
prints in CHAR/HEX/DUMP format
limiting

Format 1 :
PRINT INDATASET (entryname/passwd) -

Format 2 :
PRINT INFILE (ddname/passwd) -
parameters like REPRO are available

Options
 CHAR | DUMP | HEX
 COUNT (number)
 FROMADDRESS, [TOADDRESS]
 FROMKEY, [TOKEY]
 FROMNUMBER, [TONUMBER]
 OUTFILE (ddname)
 SKIP (number)

//DA0001TA JOB LA2179,PCS,MSGLEVEL=(1, 1) ,
// NOTIFY=DA0001T
//* Print VSAM Dataset
//PRG1 EXEC PGM=IDCAMS
//FILE1 DD DSN=DA0001T.LIB.KSDS.CLUSTER,
// DISP=SHR
//SYSPRINT DD SYSOUT = *
// SYSIN DD *
PRINT INFILE(FILE1) CHARACTER
/*
//

Example 8.4 Print VSAM Dataset

ALTER
Used to change certain attributes of a previously defined VSAM object
Following can be done with ALTER

37
VSAM

change names
 Add volumes/Remove volumes
 Change Keys and uniqueness
 Change record size
 Change Upgrade option
 Change % of FREESPACE etc.

Format:
ALTER entryname/password parameters

Options:
 ADDVOLUMES (volumes)
 AUTHORIZATION(entry string)
 BUFFERSPACE (size)
 ERASE | NOERASE
 FREESPACE(ci% ca%)
 MASTERPW(password)
 NEWNAME(newname)
 READPW (password)
 SCRATCH | NOSCRATCH
 SHAREOPTIONS
 (cross region cross system)
 TO(date) |FOR(days)
 UPDATE | NOUPDATE
 UPDATEPW(password)
 UPGRADE | NOUPGRADE

The ORDERED Parameter

The ORDERED Parameter tells VSAM to assign the KEYRANGES values to the volumes, one by
one, in the order in which the KEYRANGES and VOLUMES are specified.

Format:
ORDERED | UNORDERED

Example :
KEYRANGES( (0001 1000) -
(1001 2000) -
(2001 3000)) -
VOLUMES (BS3013 -
BS3014 -
BS3001)
Note: When you code ORDERED, you must code the same no. of VOLUMES as KEYRANGES.

The IMBED Parameter

The IMBED Parameter directs VSAM to place the sequence set on the first track of the Data Control
Area and duplicate it as many times as it will fit.
Advantage: reduces rotational delay

Format:
IMBED | NOIMBED

38
VSAM

The REPLICATE Parameter

The REPLICATE Parameter directs VSAM to duplicate each index record as many times as it will fit
on its assigned track. It applies to a KSDS index component only.

Format:
REPLICATE | NOREPLICATE

Example:
INDEX(NAME(DA0001T.LIB.KSDS.INDEX) -
IMBED -
REPLICATE -
)

The Password Protection Parameter

VSAM provides a hierarchical list of parameters that you can specify for a non-DFSMS-managed
VSAM dataset. However DFSMS-managed dataset you must use a security package like RACF.

Format:
MASTERPW(password)

Allows the highest level of access to all cluster components, including DELETE and ALTER
authority

Format:
UPDATEPW(password)

Allows write authority to the cluster

Format:
READPW(password)

Allows read only access to the cluster

Note: Valid only for KSDS, ESDS, RRDS.
Passwords are initially specified in the DEFINE
CLUSTER

Example:
MASTERPW(TRGDEPT)

At the execution time, a password can be coded explicitly in the PASSWORD clause of a COBOL
SELECT clause

The AUTHORIZATION Parameter

AUTHORIZATION provides additional security for a VSAM cluster by naming and assembler user
verification routine (USVR).

39
VSAM

Format:
AUTHORIZATION (entry-point password)

entry-point: the name of the entry point of a USVR
written in assembly language
password: the password the routine is to verify

Note: Valid only for KSDS, ESDS, RRDS.

Example:
AUTH(MYRTN ‘TRGDEPT’)

ALTER -
DA0001T.LIB.KSDS.CLUSTER -
NEWNAME(A2000.MY.CLUSTER)

Example 8.5 Altering name of a Dataset

ALTER -
DA0001T.LIB.KSDS.INDEX -
FREESPACE(30 30)


Example 8.6 Altering FREESPACE of a Dataset

The following attributes are alterable only for empty clusters
 KEYS(length offset)
 RECORDSIZE(avg max)
 UNIQUEKEY | NONUNIQUEKEY


The following attributes are unalterable. You have to DELETE the cluster and redefine it with new
attributes.

CISZ
Cluster type,
IMBED/REPLICATE
REUSE | NOREUSE

40
VSAM

9. Generation DataSets
Although there are many different uses for sequential datasets, many sequential files have one
characteristics in common: they are used in cyclical application for example, sequential dataset that
contains transaction posted daily against a master file is cyclical; each days transactions, along with
the processing required to post them, from one cycle. Similarly a sequential dataset used to hold the
backup copy of a master file is cyclical too; each time a new backup copy is made, new cycle is
begun.

In most of the cyclical applications, it’s good idea to maintain versions of the files used for several
cycles. That way if something goes wrong, you can recreate the processing that occurred during
previous cycles to restore the affected files to a known point. Then the processing can continue from
that point

For this MVS provides a facility called generation data group, GDG is a collection of two or more
chronologically related versions of the same file. Each version of the file or member of the GDG, is
called a generation dataset. A generation dataset may reside on tape or DASD. It is generally
sequential (QSAM) or direct(BDAM) file. ISAM and VSAM files can’t be used in GDGs.

As each processing cycle occurs a new generation of dataset is added to the generation data group.
The new version becomes the current generation; it replaces the old current generation, which
becomes a previous generation.

file.c1(+1) Next Generation
file.c1(0) Current Generation
file.c1(-1) Previous Generations
file.c1(-2)
file.c1(-3)

Figure above is the structure of a generation data group. There are 3 previous generations, note that
generations are numbered relative to the current generation, file.c1(0).

Relative generation numbers are adjusted when each processing cycle completes, so that the current
generation is always referred to as relative generation 0.
MVS uses the generation data group’s catalog entry to keep track of relative generation numbers. As a
result, GDGs must be cataloged and each generation dataset that’s a part of the group must be
cataloged too.

When you create a generation data group’s catalog entry, you specify how many generations should
be maintained Example: You might specify that five generations including the current generation
should be maintained. Then during each processing cycle, the new version of the file becomes the
current version.

Although MVS lets you use relative generation numbers to simplify cyclical processing, MVS uses
“Absolute Generation Numbers” in the form GnnnnV00 to identify each generation dataset uniquely.
GnnnnV00 represents the chronological sequence number of the sequence number of the generation,
beginning with G0000.

41
VSAM

V00 is a version number, which lets you maintain more than one version of a generation. Each time a
new generation dataset is created, mvs adds one the sequence number. The sequence and version
numbers are stored as a part of the file’s dataset name, like this:

filename.GnnnnV00

35 chars 9 chars

// IN DD DSN=DA0002T.MASTER, DISP=SHR

// OUT DD DSN=DA0002T.MASTER.DAY(+1),
DISP= (NEW,CATLG,DELETE),
UNIT=3390, VOL=SER=BP0031,
SPACE= (CYL,(10,5),RLSE),
DCB=(PROD.GDGMOD,
BLKSIZE=23440,LRECL=80,RECFM=FB)\

Example 9.1 Using a GDG

Relative Name and Absolute Name

DA0002T.MASTER.DAY90) ---> Relative Name
DA0002T.MASTER.DAY.G00001V00 -->Absolute Name

// Step1 EXEC PGM=IDCAMS
// SYSPRINT DD SYSOUT = *
// SYSIN DD *
DEFINE GDG
(NAME(DA0002T.MASTER.DAY)
LIMIT(5)
SCRACH
EMPTY)
/*
Example 9.2 Defining a GDG Index

Following code contains 1 job with 2 steps....

//DA0003TA JOB
//UPDATE EXEC PGM=PAY3200
//OLDMAST DD DSN=MMA2.PAY.MAST(0),DISP=OLD
//NEWMAST DD DSN=MMA2.PAY.MAST(+1),
DISP= (NEW,CATLG),UNIT=3300,
VOL=SER=BS3001,
DCB=(LRECL=80,BLKSIZE=1600)
//PAYTRAN DD DSN=MMA2.PAY.TRAN,DISP=OLD
//PAYLIST DD SYSOUT=*
//REPORT EXEC PGM=PAY3300
//PAYMAST DD DSN=MMA2.PAY.MAST(+1),DISP=OLD
//PAYRPT DD SYSOUT=*

Example 9.3a Adding datasets to a GDG

42
VSAM

Following code contains 2 jobs.........

//JOB1 JOB
//UPDATE EXEC PGM=PAY3200
//OLDMAST DD DSN=MMA2.PAY.MAST(0),DISP=OLD
//NEWMAST DSN=MMA2.PAY.MAST(+1),
DISP=(NEW, CATLG), UNIT=3300,
VOL=SER=BS3001,
DCB=(LRECL=80, BLKSIZE=1600)
//PAYTRAN DD DSN=MMA2.PAY.TRAN,DISP=OLD
//PAYLIST DD SYSOUT =*
//JOB2 JOB ...........
//REPORT EXEC PGM=PAY3300
//PAYMAST DD DSN=MMA2.PAY.MAST(0),DISP=OLD
//PAYRPT DD SYSOUT=*

Example 9.3b Adding datasets to a GDG

GDG’s are a group of datasets which are related to each other chronologically and functionally.
Generations can continue until a specified limit is reached. The LIMIT parameter specifies total
number of generations that can exist at any one time. Once limit is reached the oldest generation is
deleted.

GDG Index have to be created using the IDCAMS command ‘DEFINE GDG’ before datasets that are
to be included in them can be made a part of them.
Model containing parameter information of the datasets to be included in the GDG has to be specified.
All datasets within a GDG will have the same name. Generation number of a dataset, within a GDG is
automatically assigned by OS when created. Datasets within a GDG can be referenced by their
relative generation number. Generation 0 always references current generation

Creation of GDGs

Create and catalog the index
Use IDCAMS statement DEFINE GDG for creating Index
Parameters for creating index

Specification

Name of GDG
Number of generations
Limit …. maximum no of datasets in a GDG.
Action to be taken when limit is reached

 Uncataloging oldest generation once limit reached
 Uncataloging all generations when limit reached

Physical deletion of entry
Uncataloging entry without physical deletion

Defining a model for the GDG.

NAME …… refers to the name of the GDG Index
LIMIT ….. refers to the maximum no of datasets in a GDG.

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VSAM

NOEMPTY…
EMPTY …
SCRATCH ….
NOSCRATCH …

Modifying Features of GDG

You can modify a GDG only with the ALTER command

//STEP1 EXEC PGM=IDCAMS
//SYSIN DD
ALTER DA0001T.ACCOUNTS.MONTHLY -
NOSCRATCH -
EMPTY
/*
//

Example 9.4 Modifying a GDG

Deleting GDG Index

Can be deleted by the DELETE parameter of IDCAMS
Will result in an error on reference to any generation datasets of the GDG

/STEP1 EXEC PGM=IDCAMS
//SYSIN DD
DELETE DA0001T.ACCOUNTS.MONTHLY GDG
/*
//

Example 9.5 Deleting GDG Index

Adding a Dataset to a GDG

Name of the model containing the GDG DCB parameter’s is coded in the DCB parameter of the DD
statement

//STEP1 EXEC PGM=GDG1
//FILE1 DD
// DSN=DA0001T.ACCOUNTS.MONTHLY (+1),
// DISP=(NEW,CATLG,DELETE),UNIT=SYSDA,
// SPACE=(TRK,(30,10),RLSE),
// DCB=(MODEL.DCB,
// RECFM=FB,LRECL=80,
// BLKSIZE=800)
Example 9.6 Adding a Dataset to a GDG

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VSAM

Deleting GDG Index and Datasets

FORCE parameter in the DELETE statement of IDCAMS can be used

Example :

/STEP1 EXEC PGM=IDCAMS
//SYSIN DD
DELETE DA0001T.ACCOUNTS.MONTHLY` -
GDG -
FORCE
/*
//
Example 9.7 Deleting GDG Index and Datasets

45
VSAM

10. COBOL VSAM Considerations
SELECT CLAUSE

SELECT file ASSIGN TO DDNAME / AS-DDNAME

ORGANIZATION IS SEQUENTIAL/INDEXED/RELATIVE
ACCESS MODE IS SEQUENTIAL/INDEXED/DYNAMIC
RECORD KEY IS primary Key Dataname
ALTERNATE KEY IS Alternate Key Dataname [With Duplicates]
FILE STATUS IS status-key.

Example 10.1 SELECT clause for VSAM datasets

status key=Cobol, VSAM
x(2) 9(2) - Return code
9(1) - Junction code
9(3) - Feedback code

FD Entry

Should have the record structure

If KSDS then key field must match with length and position of KEYS parameter in DEFINE
CLUSTER information

File Processing

Regular COBOL file handling commands

Alternate index processing:

In JCL there must be a DD statement for base cluster and one or more DD statement for alternate
index path name.

Note: There is no COBOL standard for assigning ddnames to alternate indexes, so a quasi-standard has
emerged whereby a sequential number is appended to the eighth character of the base cluster ddname.

//LIBMAST DD DSN=DA0001T.LIB.KSDS.CLUSTER,
// DISP=SHR
//LIBMAST1 DD DSN=DA0001T.LIB.KSDS.NAME.PATH,
// DISP=SHR
//LIBMAST2 DD DSN=DA0001T.LIB.KSDS.DEPT.PATH,
// DISP=SHR
Example 10.2 JCL to access AIX

Remark:
No matter how many alternate indexes you specify in the program, there’s only one ASSIGN clause
pointing to the ddname of the base cluster.

46
VSAM

SELECT file ASSIGN TO LIBMAST

RECORD KEY IS............
ALTERNATE KEY IS.........
[WITH DUPLICATES]

Example 10.3 Cobol SELECT clause for AIX

FD: Should have record description having primary key dataname and alternate key dataname

KEY of reference: READ filename
KEY IS primary/alternate key
dataname

Key of Reference.

The key that is currently being used to access records is called the key of reference. When the
program opens the dataset, the primary key becomes, by default, the key of reference. The primary
key remains the key of reference when accessing records until it is changed. To start accessing records
by an alternate index key, you merely change the key of reference by using the KEY phrase as part of
one of the following statements.

A random READ statement, for example

READ EMP-MAST KEY IS EMP-NAME
Example 10.4 READ

A sequential READ statement, for example

READ EMP-MAST NEXT
KEY IS EMP-NAMEA

Example 10.5 READ for Accessing AIX

START statement, for example

START EMP-MAST
KEY IS EQUAL TO EMP-NAME.
Example 10.6 START verb

key-1 key-2 Cause
Successful Completion:
0 0 No further information,
2 Duplicate key detected.
4 Wrong fixed-length record.
5 Data set created when pened.With
sequential VSAM datasets,0 is returned.
7 CLOSE with NO REWIND or
REEL, for non-tape.
End-of-file.
1 0 No further information.
4 Relative record READ outside

47
VSAM

dataset boundary.

Invalid key.
2 1 Sequence error.
2 Duplicate key.
3 No record found.
4 Key outside boundary of dataset.

Permanent I/O error :
3 0 No further information.
4 Record outside dataset boundary.
5 OPEN and required dataset not found.
7 OPEN with invalid mode.
8 OPEN of dataset closed with LOCK.
9 OPEN unsuccessful because of
conflicting dataset attributes.

Logic error :
4 1 OPEN of dataset already open.
2 CLOSE for dataset not open.
3 READ not executed before REWRITE.
4 REWRITE of different-record size.
6 READ after EOF reached.
7 READ attempted for dataset not opened I-O
or INPUT.
8 WRITE for dataset not opened OUTPUT,I-O
or EXTEND.
9 DELETE or REWRITE for dataset not opened I-O.

Specific compiler-defined conditions :
9 0 No further information.
1 VSAM password failure.
2 Logic error.
3 VSAM resource not available.
4 VSAM sequential record not available.
5 VSAM invalid or incomplete dataset information.
9 6 VSAM-no DD statement.
7 VSAM OPEN successful. Dataset integrity verified.

VSAM I/O error processing

I/O error handling is one vital area where VSAM dataset processing differs from non-VSAM dataset
processing. When processing non-VSAM datasets, most programmers code their application
programs to ignore errors, because the access method would abend the program if a serious I/O error
occurs. Not so when processing VSAM datasets.

The COBOL FILE STATUS Key

VSAM places program control in the hands of the programmer, not the O/S. For this reason, it is
important to check the COBOL status key designated in the FILE STATUS clause after every I/O
operation. For some error keys you'll want to abend the program immediately; for others you can just
display the key, the record, and an informative message and continue processing.
For these status key values, continue processing normally:

48
VSAM

00 successful I/O.
02 duplicate alternate key encountered (expected).
10 end of file.

For these status key values, bypass the record, display pertinent information, and continue processing
:

21 Input record out of sequence.
22 duplicate primary key or unique alternate key
encountered (un-expected).
23 record (or Key) not found.

Note: You may want to have the program count the number of times these key values are returned and terminate
the program if the counter reaches an unacceptable number, which would likely to indicate that your input is
bad

For the following status key values, terminate the program:

24 out-of-space condition (KSDS or RRDS).
30 Nonspecific I/O problem.
34 out-of-space condition(ESDS).
49 REWRITE attempted; dataset not opened for I-O.
90 Dataset unusable or logic error.
92 logic error.
93 Resource not available.
94 current record pointer undefined.
95 Nonzero HURBA for OPEN OUTPUT.
96 No corresponding JCL DD statement.
97 If your shop has enabled the implicit VERIFY command, this means that the dataset
was opened after and implicit VERIFY, and you can continue processing.

49
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11. Appendix-A

VSAM ASSIGNMENT
a. Define an ESDS cluster. Populate the ESDS cluster by using a COBOL program. Using
LISTCAT command list the attributes of the created cluster.

b. Define a KSDS cluster with the following options:

Allocation for 3000 records primary, secondary allocations for 100 records.
Fixed record length of 80 bytes each.
Key beginning in the 5th position with length of 5 bytes.
Volume parameters.

c. Populate the KSDS cluster by using a COBOL program. Using LISTCAT command list the
attributes of the created cluster.

d. Write a program to populate an indexed master file from transaction records. There are three
datasets.

PRODUCT-MASTER Record Layout

Prodno unit price
1 56 10

PURCHASE-TRANS Record Layout

Custno Name Qty Prodno

1 5 6 25 26 28 29 33

CUSTOMER-MASTER Record Layout

Custno Amount Prodno

1 56 13 14 18

50
VSAM

1. A table of product numbers and corresponding unit prices is to be created in storage from
PRODUCT-MASTER. There are 50 product numbers.

2. Customer number is the key field for the CUSTOMER-MASTER file

3. Amount owed = Quantity Purchased x Unit Price (from table)

4. Perform a table look up using the product number from the PURCHASE-TRANS record to
find the corresponding unit price in the PRODUCT-MASTER table.

e. An indexed file contains the following table records:

1-2 State number
3-4 County number
5-7 Tax rate
8-11 Not used

The key field is a combined group item consisting of state number and country number. Create a
KSDS cluster and populate the cluster from the following transaction records.

1-5 Customer number
6-25 Customer name
26-28 Qty
29-33 Price per unit
34-35 State number
36-37 County number
37 Not used

The output master file is also an indexed file with following record layout

1-37 Same as positions 1-37 in the transaction record
38-45 Amount Owed
46 Not used

Amount Owed = Qty x Price per unit + Tax rate x (Qty x Price per unit)

51
VSAM

12. Appendix -B

References
MVS/VSAM for Application Programmer by Brown and Smith

VSAM by Doug Lowe

VSAM for COBOL Programmer by Doug Lowe

52
VSAM

13. Appendix-C

Table of Figures
Figure 2.1 VSAM Catalog ............................................................................................................. 7
Figure 2.2 Space Allocation ........................................................................................................... 8
Figure 3.1 Contents of Control Interval ......................................................................................... 9
Figure 3.2 Contents of Control Field ............................................................................................. 9
Figure 3.3 Control Area ............................................................................................................... 10
Figure 3.4 Spanned Record .......................................................................................................... 10
Figure 3.5 Contents of Control Area ............................................................................................ 11
Figure 3.6 Contents of KSDS Index............................................................................................. 11
Figure 3.7 Contents of Sequence Set............................................................................................ 12
Figure 3.7 Contents of Index Set .................................................................................................. 12
Figure 3.8 Inserting a new record into a KSDS ........................................................................... 13
Figure 3.9 Inserting a new record into a full CI ........................................................................... 13
Figure 3.10 After Control Interval Split ......................................................................................... 14
Figure 3.11a Effect of Control Interval Split on Sequence Set.................................................. 14
Figure 3.11b Effect of Control Interval split on Sequence Set ................................................... 15
Figure 5.1 HURBA and HARBA ................................................................................................. 26
Figure 6.1 Contents of KSDS unique alternate index .................................................................. 28

53
VSAM

14. Appendix-D

Table of JCL listing
Example 4.1 JCL for executing IDCAMS commands .............................................................. 17
Example 4.2 Creating a cluster ................................................................................................... 17
Example 4.3a JCL using MAXCC and LASTCC ........................................................................ 18
Example 4.3b JCL using MAXCC and LASTCC ........................................................................ 18
Example 4.4 JCL for Defining an ESDS Cluster........................................................................ 21
Example 4.5 JCL for Defining a KSDS Cluster ......................................................................... 22
Example 5.1 LISTCAT ............................................................................................................... 25
Example 6.1 JCL to define AIX ................................................................................................. 28
Example 6.2 JCL to define PATH for the AIX .......................................................................... 29
Example 6.3 JCL to build Alternate Index ................................................................................. 30
Example 6.4 Steps for creating and building AIX ...................................................................... 30
Example 7.1 JCL for Loading Dataset: ...................................................................................... 32
Example 7.2 Using Repro for backup......................................................................................... 32
Example 7.3 DELETE-DEFINE-REPRO .................................................................................. 33
Example 7.4 Input instream Data into ESDS ............................................................................. 35
Example 7.5 Load Data from a file into ESDS........................................................................... 35
Example 8.1 VERIFY ................................................................................................................. 36
Example 8.2 Deleting a Cluster .................................................................................................. 36
Example 8.3 Delete VSAM Dataset .......................................................................................... 37
Example 8.4 Print VSAM Dataset .............................................................................................. 37
Example 8.5 Altering name of a Dataset .................................................................................... 40
Example 8.6 Altering FREESPACE of a Dataset....................................................................... 40
Example 9.1 Using a GDG ......................................................................................................... 42
Example 9.2 Defining a GDG Index .......................................................................................... 42
Example 9.3a Adding datasets to a GDG ..................................................................................... 42
Example 9.3b Adding datasets to a GDG ..................................................................................... 43
Example 9.4 Modifying a GDG.................................................................................................. 44
Example 9.5 Deleting GDG Index.............................................................................................. 44
Example 9.6 Adding a Dataset to a GDG ................................................................................... 44
Example 9.7 Deleting GDG Index and Datasets ........................................................................ 45
Example 10.1 SELECT clause for VSAM datasets ..................................................................... 46
Example 10.2 JCL to access AIX ................................................................................................. 46
Example 10.3 Cobol SELECT clause for AIX ............................................................................. 47
Example 10.4 READ .................................................................................................................... 47
Example 10.5 READ for Accessing AIX ..................................................................................... 47
Example 10.6 START verb .......................................................................................................... 47