1. VSAM
Overview

2. VSAM (Virtual Storage Access Method )
VSAM is an integral part of MVS. At the end of this course,
you, the user, will know VSAM in detail.
 know the different types of VSAM data sets
 be able to create, delete and alter VSAM data sets, with
indexes and alternate indexes
 know the organization of VSAM data sets

3. Access Methods
 An access method defines the technique by which data is
stored and retrieved. The different types of dataset
organizations in MVS are:
 Physical Sequential
 Partitioned
 Indexed Sequential
 Direct
 VSAM

4. What is VSAM?
 VSAM is Virtual Storage Access Method
 It is a method used to move data between Disk and Main
Storage
 VSAM operates in Virtual Environment

5. VSAM
 VSAM acts as interface between
 Operating System and Application Program
V
Request S Reply Operating
Application
A System
M

6. VSAM
 Interface between Main Storage and Disk
V
S
Main Storage DATA A DATA Disk
M

7. File access methods
 Data (Records) is retrieved
 Sequential (Reading from beginning to end)
 Random (Records are read by the value in the key)
 Direct (Records are read based on their physical
location/address on disk)
 VSAM provides all these methods
 One access method supporting all types of data retrieval

8. Traditional access methods
 QSAM (Queried Sequential Access Method)
 BSAM (Basic Sequential Access Method)
 for ‘flat’ files
 ISAM (Index Sequential Access Method)
 for Index files
 BDAM (Basic Direct Access Method)
 for direct access files

9. VSAM Dataset Types
Entry Sequenced Dataset (ESDS)
 ESDS contains records in the order in which they are entered. Records
are added to the end of the data set, and can be accessed sequentially.
Key Sequenced Dataset (KSDS)
 KSDS contains records in ascending collating sequence. Records can
be accessed by a field called a key, or by a relative byte address (RBA -
relative position of the record from the beginning of the dataset), or
sequentially.
Linear Dataset (LDS)
 LDS contains data that has no record boundaries. The manipulation of
the data is completely controlled by the user.
Relative Record Dataset (RRDS)
 RRDS contains records in the order of relative record number. These
records can be accessed only by this number.

10. VSAM data set organization
 VSAM Data Set can contain three major components
 CLUSTER (Catalog entry)
 INDEX
 DATA (Actual data)
 Data Set is referred by cluster name in JCL
INDEX
CLUSTER
DATA

11. VSAM internals
 CONTROL INTERVAL (CI)
 VSAM stores Data and Index in Control Intervals (CI)
 CI is similar to ‘Block’
CI
Record Record .......

12. CONTROL INTERVAL
 CI is the unit of retrieval between DASD and I/O Buffer (Virtual
Storage)
DASD I/O Buffer
CI
R1 R2 R3 R1 R2 R3

13. Control Interval
 CI contains
 Records (or DATA)
 Free space (Optional)
 Control Information Definition Field (CIDF)
 Record Definition field (RDF)

14. Building blocks of a VSAM Dataset
Logical Record
 Logical records of VSAM data sets are stored in a different manner from logical
records in non-VSAM data sets. VSAM stores records in control intervals.
Control Interval (CI)
A control interval consists of the following:
 Logical records (LR)
 Free space (FS)
 Control information fields
LR LR LR LR..FS....FS...RDF CIDF
 Free Space is the space reserved within the CI for inserting new records in a KSDS or
for lengthening the existing records.

15. CONTROL INTERVAL
 CIDF & RDF are VSAM control functions
 Used by VSAM to access data
R R C
R1 R2 Free D I
R3 D
Space F D
F
F
3 bytes, Length of Record
How many successive
records have same length 4 bytes long, One per CI
Indicates Free space,
where and how much

16. CONTROL AREA
Control Area
 CIs are grouped into CA
 The control intervals in a VSAM data set are grouped together
into Control Areas.
 A VSAM data set is actually composed of one or more control
areas. The maximum size of a control area is a cylinder, and
the minimum size is one track.
Control Area
(CA)
LR LR LR LR.. FS....FS... RDF CIDF
LR LR LR LR.. FS....FS... RDF CIDF
LR LR LR LR.. FS....FS... RDF CIDF

17. Cluster
 VSAM datasets are defined as Highest Index Set
Clusters. 2210 5000
 A Cluster is a combination of the
data component and the index Index Set
component. 1055 1600 FS 5000 FS FS
 The Index component is applicable
only in the case of a KSDS. Sequence Set
 The data component holds data 1010 1055 FS 1350 1600 FS
records.
 The index component holds the
index records to access the required DATA COMPONENT (CA1)
information from the data
component 1300 1305 1310 1350 FS
1400 1410 1415 1600 FS
Data Component (CA2)
FS FS FS FS FS
1001 1002 1005 1010 FS
1020 1022 1030 1055 FS
FS FS FS FS FS

18. Control Interval Split
CA-1 (CI-1 to CI-3) - Before split
 When a data set is first loaded,
the key sequence of records and 1001 1002 1005 1010 FS
their physical order are the same.
 However, when records are 1020 1022 1030 1055 FS
inserted, control interval split can
occur, causing the data control
intervals to have a physical order FS FS FS FS
that is different from the key
sequence.
 For example, try to insert '1004' CA-1 (CI-1 to CI-3) - After split
in CI-1 shown below :
 A Control Interval Split occurs
1001 1002 1004 FS
and CI-1 is split exactly into two
half CI's. CI-3, which is a free 1020 1022 1030 1055 FS
control interval is used, and some
logical records of CI-1 are moved
into CI-3. CI-3 is placed after CI- 1005 1010 FS FS
2 and it is not inserted in between
CI-1 and CI-2.

19. Control Area Split
 Now, if record ‘1025’ is inserted, there is no free control
interval for a CI split to occur. Hence, a CA (control area)
split occurs. The CA-1 is split into two half control areas;
some of the Control intervals of CA-1 are moved into the
newly created CA (CA-2).
CA-1 (CI-1 to CI-3) - After split
1001 1002 1004 FS
1020 1022 FS FS FS
FS FS FS FS
CA-2 (CI-1 to CI-3)
1025 1030 1055 FS
1005 1010 FS FS
FS FS FS FS

20. Types of VSAM data sets
 ESDS Entry Sequenced Data Set
 KSDS Key Sequenced Data Set
 RRDS Relative Record Data Set
 LDS Linear Data Set

21. ORGANIZATION
SEQUENTIAL => ESDS
INDEXED => KSDS
RELATIVE => RRDS
ACCESS MODE OPTIONS
ESDS : SEQUENTIAL
KSDS : SEQUENTIAL or RANDOM or DYNAMIC
RRDS: SEQUENTIAL or RANDOM or DYNAMIC

22. Access Method Services (AMS)
 Access Method Services is a service program that helps you to
allocate and maintain VSAM data sets and catalogs.
 IDCAMS is the name of the utility program used to perform the
following operations on VSAM data sets.
 Creating a Data set
 Loading a VSAM data set.
 Printing a Data set
 Deleting a Data set
 Error Detection for KSDS Data set
 Creating Generation Data Groups (GDG) etc.

23. INVOKING ACCESS
METHOD
IDCAMS UTLITY

24. Defining a VSAM Cluster
 The Define Cluster command is used to allocate VSAM data sets. The basic information
required for defining a VSAM data set is:
 Name of the cluster.
 Volume(s) on which the data set will be allocated.
 Type of data set (KSDS, ESDS, RRDS or LDS).
 Space needed for the data set.
 For a KSDS, the length of the key and its offset from the beginning of the record.
 Record size, and whether it is fixed or variable in length.
 Control interval size.
 CI and CA Free Space.
 The following keywords have to be used to define the different types of VSAM data sets:
 NONINDEXED for ESDS.
 INDEXED for KSDS.
 NUMBERED for RRDS.
 LINEAR for LDS.

25. Sample JCL to create an ESDS cluster
//LEM0UXXA JOB
MSGCLASS=Q,CLASS=Q,NOTIFY=&SYSUID
//DEFKSDS EXEC PGM=IDCAMS NONINDEXED - ESDS
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
DEFINE CLUSTER(NAME(LEM0UXX.TEST.ESDS) -
VOLUMES(LEM001) -
RECORDSIZE(N1,N2)
NONINDEXED -
TRACKS(2,1) - N1=> AVG RECL
RECORDSIZE(50,50) - N2=> MAX RECL
CONTROLINTERVALSIZE(4096) -
FREESPACE(10,20)) -
DATA(NAME(LEM0UXX.TEST.ESDS.DATA))
/*
Freespace(PCT1,PCT2)
PCT1=> PCT FREE SPACE IN each CI
PCT2=> PCT Of unused CI in CA

26. COBOL AND ESDS
OVERVIEW

27. ESDS
 Similar to Sequential File
 Sequenced by the order in which data is entered/loaded
 New Records are added at the end only (chronological order)
 Supports both Fixed and Variable formats
 Contains only CLUSTER & DATA components

28. ESDS (Contd...)
 Only sequential access in Batch Cobol Programs
 Random access is supported in on-line applications (CICS)
using Relative Byte Address (RBA)
 Alternate Index is supported in on-line applications (CICS)
 NO primary index

29. RBA
 Record location relative to the beginning of the file
(Relative Byte Address)
CI
R1 R2 R3
80 40 60
RBA of R1 is 80

30. FILE-CONTROL Paragraph
Format:
SELECT [OPTIONAL] File-name-1 ASSIGN TO AS-Assignment-name-1
SEQUENTIAL
[ ORGANIZATION IS INDEXED
RELATIVE
SEQUENTIAL
[ACCESS MODE IS RANDOM
DYNAMIC
[FILE STATUS IS Data-name-1]

31. ESDS
 ORGANIZATION IS SEQUENTIAL
 ACCESS MODE IS SEQUENTIAL
INPUT OUTPUT INPUT- EXTEND
OUTPUT
READ YES - YES -
WRITE - YES YES
DELETE
REWRITE YES

32. VSAM === ESDS
ORGANIZATION IS SEQUENTIAL.
ACCESS MODE = SEQUENTIAL
OVERVIEW

33. CREATING ESDS

34. Writing Data in ESDS

35. Writing Data in ESDS

36. Writing Data in ESDS

37. RUNNING A PROGRAM

38. View the data from ESDS
REPRO COMMAND

39. PRINT ESDS EXAMPLE
Overview

40. PRINT ESDS

41. PRINT ESDS

42. PRINT ESDS

43. KSDS (KEY SEQUENTIAL
DATA SET )

44. Sample JCL to create a KSDS cluster
KEYS(N1,N2)
//LEM0UXXA JOB MSGCLASS=Q,CLASS=Q,NOTIFY=&SYSUID N1=> length of the Key(Bytes)
//DEFKSDS EXEC PGM=IDCAMS N2=> is starting byte position
//SYSPRINT DD SYSOUT=* of Key in Record
//SYSIN DD *
DEFINE CLUSTER(NAME(LEM0UXX.TEST.KSDS) - RECORDSIZE(N1,N2)
VOLUMES(LEM001) - N1=> AVG RECL
TRACKS(2,1) -
N2=> MAX RECL
INDEXED -
KEYS(9,0) -
INDEXED - KSDS
RECORDSIZE(50,50) -
CONTROLINTERVALSIZE(4096) -
Freespace(PCT1,PCT2)
FREESPACE(10,20)) -
PCT1=> PCT FREE SPACE IN each CI
DATA(NAME(LEM0UXX.TEST.KSDS.DATA)) -
PCT2=> PCT Of unused CI in CA
INDEX((NAME(LEM0UXX.TEST.KSDS.INDEX))

45. SELECT & ASSIGN Syntax
ENVIRONMENT DIVISION.
INP UT- OUT P UTSECT ION.
FILE - CONT ROL.
SELECT [OP T IONAL FileName
]
ASSIGN T O FileSpec
ORGANIZAT I IS INDEXED
ON
SEQUENT IAL
ACCESS MODE IS RANDOM
DYNAMIC
RECORD KEY IS UniqueRecKey
ALT ERNAT ERECORD KEY IS AltKey WIT HDUP LICAT ES
FILE ST AT US IS FileStatus

46. READ statement
READ FileName RECORD INTO DestItem
KEY IS KeyName
INVALID KEY StatementBlock
END READ
READ FileName NEXT RECORD INTO DestItem
AT END StatementBlock
END READ

47. WRITE & REWRITE statement
WRITE RecName FROM SourceItem
INVALID KEY StatementBlock
END WRITE
REWRITE RecName FROM SourceItem
INVALID KEY StatementBlock
END REWRITE

48. KSDS
 ORGANIZATION IS INDEXED
 ACCESS MODE IS SEQUENTIAL
INPUT OUTPUT INPUT-
OUTPUT
READ YES - YES
WRITE - YES
DELETE YES
REWRITE YES
START YES YES

49. INDEX FILE
ORGANIZATION IS INDEXED.
ACCESS MODE = SEQUENTIAL
OVERVIEW

50. CREATING KSDS

51. WRITING A KSDS

52. WRITING A KSDS

53. WRITING KSDS

54. RUNNING A KSDS

55. Running a KSDS

56. READING INDEX FILE-KSDS
ORGANIZATION IS INDEXED.
ACCESS MODE = SEQUENTIAL
OVERVIEW

57. READING A KSDS

58. READING A KSDS FILE

59. EXECUTE A PROGRAM FOR READING DATA
FROM KSDS

60. SPOOL OUTPUT

61. SPOOL OUTPUT

62. START & DELETE statement
IS EQUAL TO
IS =
IS GREATER THAN
START FileName KEY KeyName
IS >
IS NOT LESS THAN
IS NOT <
INVALID KEY StatementBlock
END START
DELETE FileName RECORD
INVALID KEY StatementBlock
END DELETE

63. START :Position a Record

64. START COMMAND

65. START COMMAND

66. DELETE COMMAND

67. DELETE COMMAND

68. EXECUTE A PROGRAM AFTER COMPILE

69. PRINT THE KSDS DATASET

70. PRINT THE KSDS

71. KSDS
ORGANIZATION IS INDEXED
ACCESS MODE IS RANDOM

72. KSDS
 ORGANIZATION IS INDEXED
 ACCESS MODE IS RANDOM
INPUT OUTPUT INPUT-
OUTPUT
READ YES - YES
WRITE - YES YES
DELETE YES
REWRITE YES
START

73. KSDS – RANDOM- WRITE

74. KSDS – Random -WRITE

75. KSDS –RANDOM MODE
READ Operation
Overview

76. KSDS – RANDOM -READ

77. KSDS – RANDOM -READ

78. KSDS
ORGANIZATION IS INDEXED
ACCESS MODE IS DYNAMIC

79. KSDS
 ORGANIZATION IS INDEXED
 ACCESS MODE IS DYNAMIC
INPUT OUTPUT INPUT-
OUTPUT
READ YES - YES
WRITE - YES YES
DELETE YES
REWRITE YES
START YES YES

80. KSDS- DYNAMIC MODE
WRITE OPERATION
Overview

81. KSDS –DYNAMIC- WRITE

82. KSDS –DYNAMIC-WRITE

83. KSDS –DYNAMIC-READ

84. KSDS-DYNAMIC-READ

85. RRDS
Overview

86. Sample JCL to create an RRDS cluster
//LEM0UXXA JOB
MSGCLASS=Q,CLASS=Q,NOTIFY=&SYSUID
//DEFRRDS EXEC PGM=IDCAMS NUMBERED - RRDS
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
DEFINE CLUSTER(NAME(LEM0UXX.TEST.RRDS) -
RECORDSIZE(N1,N2)
VOLUMES(LEM001) -
N1=> AVG RECL
NUMBERED -
N2=> MAX RECL
TRACKS(2,1) -
RECORDSIZE(50,50) -
CONTROLINTERVALSIZE(4096) -
Freespace(PCT1,PCT2)
FREESPACE(10,20)) -
PCT1=> PCT FREE SPACE IN each CI
DATA(NAME(LEM0UXX.TEST.RRDS.DATA))
PCT2=> PCT Of unused CI in CA
/*

87. RELATIVE-RANDOM-WRITE

88. RELATIVE-RANDOM-WRITE

89. RELATIVE-RANDOM-READ

90. RELATIVE-RANDOM-READ

91. RANDOM READ JCL

92. SPOOL OUTPUT

93. RELATIVE-DYNAMIC-READ

94. RELATIVE-DYNAMIC-READ

95. RELATIVE-DYNAMIC-READ

96. ALTERNATE INDEX
Overview

97. ALTERNATE INDEXES
 Used whenever the data is required to be retrieved on the basis of m
than one field
EMPNO ENAME SALARY
101 RAJESH 5000
102 RAMESH 6000
103 RANDY 7000
104 SURESH 8000
 e.g., Can be defined for both KSDS & ESDS
EMPNO IS ENAME IS
BASE KEY ALTERNATE KEY

98. ALTERNATE INDEXES
Reduce data redundancy
Can have duplicates
Easy to define using IDCAMS
Allow datasets to be accessed sequentially or
randomly
Can be updated automatically

99. Disadvantages
 Performance degradation
 Complex update logic

100. Steps for Creating Alternate Index
 Define AIX using IDCAMS DEFINE AIX
 Specify Alternate Index Path using IDCAMS DEFINE PATH
 Build AIX & populate it using IDCAMS BLDINDEX

101. Sample JCL to create an AIX cluster
UPGRADE-> VSAM AUTOMATIC
Updates the AIX for all
ADD,UPDT,DEL of Base cluster
//LEM0UXXA JOB
MSGCLASS=Q,CLASS=Q,NOTIFY=&SYSUID
//DEFKSDS EXEC PGM=IDCAMS
UNIQUE /NONUNIQUE
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
DEFINE AIX (NAME(LEM0UXX.TEST.AIX.CLUSTER) –
KEY ( N1,N2)
RELATE (LEM0UXX.INFILE.KSDS) - N1-> LENGTH OF AIX key
VOLUMES(LEM001) -
KEY (10, 35) - N2-> KEYS start Loc in BASE CLUSTER
TRACKS(2,1) -
NONUNIQUEKEY - RECORDSIZE(N1,N2)
RECORDSIZE(49,49) -
N1=> AVG RECL
UPGRADE
CONTROLINTERVALSIZE(4096) - N2=> MAX RECL
FREESPACE(10,20)) -
DATA(NAME(LEM0UXX.TEST.AIX.DATA))
INDEX(NAME(LEM0UXX.TEST.AIX.INDEX)) Freespace(PCT1,PCT2)
/*
PCT1=> PCT FREE SPACE IN each CI
PCT2=> PCT Of unused CI in CA

102. UPGRADE/NOUPGRADE
• Syntax : UPGRADE/NOUPGRADE
• UPGRADE specifies that records
in AIX are to be updated
• automatically whenever the
base cluster is updated

103. BUILDING AN INDEX
Overview

104. BUILD INDEX
//JOB CARD
//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
BUILD INDEX is used
//SYSIN DD *
To load records in
BLDINDEX -
INDATASET(LEM0UXX.KSDS.CLUSTER') - AIX after it has been def
OUTDATASET('LEM0UXX.KSDS.AIX.CLUSTER') -
/*

105. PATH AND ALTERNATE
INDEX
Overview

106. DEFINE PATH
//JOB CARD
//STEP1 EXEC PGM = IDCAMS Path Establishes
//SYSPRINT DD SYSOUT=* A Bridge Between
//SYSIN DD * BASE CLUSTER & AIX
DEFINE PATH -
( NAME ( LEM0UXX.KSDS.PATH) –
PATHENTRY(LEM0UXX.KSDS.AIX.CLUSTER) –
UPDATE )
/*
//

107. ALTERNATE Index
Example

108. Define BASE CLUSTER

109. LOADING DATA INTO BASE CLUSTER

110. LOADING DATA INTO BASE CLUSTER

111. LOADING DATA INTO BASE CLUSTER

112. EXECUTING A PROGRAM TO LOAD DATA

113. EXECUTING A PROGRAM TO LOAD DATA

114. DEFINING AIX
RECORDSIZE(N1,N2)
N1= LENGTH OF BASE CLUSTER KEY(3)
+ LENGTH OF AIX KEY(5) + 5 for CI

115. Build index

116. Create path for Bridge

117. READING RECORDS BY ALTERNATE INDEX

118. READING RECORD BY ALTERNATE KEY

119. READING RECORD BY ALTERNATE KEY

120. EXECUTE A READ PROGRAM BY ALTERNATE
KEY
DD1-> BASE CLUSTER
DD11-> PATH NAME
DDNAME SHOULD BE IN ORD

121. SPOOL OUTPUT

122. IDCAMS REPRO

123. IDCAMS REPRO KEY BASED

124. IDCAMS REPRO RELATIVE

125. IDCAMS LISTCAT

126. SPOOL OUTPUT

127. IDCAMS DELETE