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A complete overview on VSAM (Virtual Storage Access Methods)-by rohitkapa

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  1. 1. VSAMComplete Overview
  2. 2. Sessions Outline• Session 1 : Introduction to VSAM• Session 2 : Structure of VSAM Datasets• Session 3 : Access Method Services• Session 4 : Demo/Exercise Discussion 2
  3. 3. Objectives• Familiarization with – VSAM concepts – Space Allocation and types of data sets supported by VSAM – VSAM Characteristics• Identify the general uses for Access Method Services 3
  4. 4. Introduction to VSAM(Virtual Storage Access Method) • Session 1 4
  5. 5. Topics Covered• VSAM Basics• VSAM Dataset Organization 5
  6. 6. What is VSAM?• VSAM is a high-performance access method used in OS/390, MVS/ESA and z/OS operating systems• Used as a Dataset in conjunction with programming languages (COBOL or PL/I) to create Applications• Used by CICS to store and retrieve data• Not a database management system – does not provide a relationship among data (such as DB2 or IMS) 6
  7. 7. VSAM Characteristics• VSAM supports three types of data access: Sequential, Random (also called Direct access) and Skip Sequential• Protection of data against unauthorized access is an inherent part of VSAM• Easily portable to AS/400, the PC or non-IBM computers (cross system compatibility)• A format for storing data independently of the type of direct access storage device on which it is stored 7
  8. 8. VSAM Characteristics (Contd.)• Options for optimizing performance• A multifunction service program (Access Method Services - IDCAMS) for setting up catalog records and maintaining data sets• Transactional VSAM - allows VSAM data set sharing in batch/online and batch/batch environments 8
  9. 9. VSAM Dataset Organizations• ESDS Entry Sequenced Data Set• KSDS Key Sequenced Data Set• RRDS (Fixed Length) Relative Record Data Set• VRRDS Variable Length Relative Record Data Set• LDS Linear Data Set 9
  10. 10. NON-VSAM Access Methods• BSAM : Basic Sequential Access Method• QSAM : Queued Sequential Access Method• ISAM : Indexed Sequential Access Method• BDAM : Basic Direct Access Method 10
  11. 11. Similarities between VSAM & NON-VSAM Datasets • VSAM type Similar to – KSDS ISAM – ESDS BSAM/QSAM – RRDS BDAM 11
  12. 12. VSAM Dataset Organization • 12
  13. 13. Topics Covered• VSAM Catalog Structure – VSAM Terminology• VSAM Record Storage – Control Intervals and Control Areas 13
  14. 14. VSAM Terminology• Catalog Management • Record management • Data component• Logical Record • Master/User Catalog• Key Field • Data Space• Physical Record • Control Interval and Control Area• Cluster • Alternate Indexes• Sphere • Spanned Records• Index component 14
  15. 15. Catalog Management• VSAM maintains extensive information about data sets and direct access storage space in an integrated catalog facility (ICF) catalog.• The catalog’s collection of information about a data set defines that data set’s characteristics. All VSAM files must be defined in an ICF catalog. 15
  16. 16. Record Management• The record management part of VSAM contains the access method code. 16
  17. 17. Logical record• Unit of information used to store data in a VSAM data set.• Set of bytes containing a logical description of an item processed by an application program.• A logical record can be of a fixed size or a variable size depending on the business requirements. 17
  18. 18. Key field• Identifies the item associated with the logical record.• Important Field whose contents can be used to retrieve the specific logical record 18
  19. 19. Physical record• The data is usually a set of logical records (packed together) transferred from or to memory by just one Read or Write CCW. The access method uses the BLKSIZE parameter to determine the length of the physical record. A large block size results in fewer gaps in the track but larger buffer in memory to keep the data.• A physical record is device dependent, its size is calculated at the time the data set is defined.• All physical records have the same length. 19
  20. 20. Cluster• Collection of physical datasets that make up one logical data set.• Consists of Data Component or Data Component & Index Component 20
  21. 21. Sphere• A sphere is a base VSAM cluster and its associated clusters.• These associated clusters are the alternate indexes (AIXs) of the base cluster. 21
  22. 22. Data and Index Component• A component is an individual part of a VSAM data set. Each component has a name, an entry in the catalog and an entry in the VTOC.• The KSDS and VRRDS organizations have data and index components. ESDS, RRDS and LDS organizations only have data components.• The data component is the part of a VSAM data set, alternate index, or catalog that contains the data records.• Using the Index component VSAM is able to randomly retrieve a record from the data component when a request is made for a record with a certain key. The key determines the record’s position in the data set. 22
  23. 23. Control Interval and Control Area• It is the fundamental building block of every VSAM file.A CI is a contiguous area of direct access storage that VSAM uses to store data records and control information that describes the records.• A CI is the unit of information that VSAM transfers between the storage device and the process or during one I/O operation. Whenever a record is retrieved from direct access storage, the entire CI containing the record is read into a VSAM I/O buffer in virtual storage. The desired record is transferred from the VSAM buffer to a user-defined buffer or work area.• A CA is formed by two or more CIs put together into fixed-length contiguous areas of direct access storage. A VSAM data set is composed of one or more CAs. CAs are needed to implement the concept of splits. The size of a VSAM file is always a multiple of its CA. VSAM files are extended in units of CAs. A spanned record cannot be larger than a CA. 23
  24. 24. Alternate Indexes• Alternate indexes (AIXs) allows logical records of a KSDS or of an ESDS to be accessed sequentially and directly by more than one key field.• AIXs eliminate the need to store the same data in different sequences in multiple data sets for the purposes of various applications. Each alternate index is a KSDS cluster consisting of an index component and a data component. 24
  25. 25. Spanned Records• Spanned records are needed when the application requires very long logical records. A spanned record may be the data component of an AIX cluster. If spanned records are used for KSDS, the primary key must be within the first control interval.• Spanned records are logical records that are larger than the CI size. To have spanned records, the file must be defined with the SPANNED attribute at the time it is created. Spanned records are allowed to extend across or span control interval boundaries.• A spanned record must always begin on a control interval boundary and fills one or more control intervals within a single control area. A spanned record cannot share the CI with any other records. 25
  26. 26. Control Intervals and Control Areas • 26
  27. 27. Control Interval• VSAM Basic unit of work – the minimum amount of data that is transferred via buffers, between DASD and Main Memory• VSAM determines the size of the physical Record (BLOCK) based on CI Size• The CI size can be from 512 byes to 32 KB 27
  28. 28. Control Interval & Control Area• CA is a fixed length area of auxiliary storage space in which VSAM stores records• Logical records of a VSAM dataset are grouped into a number of CIs.• CIs of a dataset are grouped into one or more CAs• The size of a VSAM file is always a multiple of its CA 28
  29. 29. General format of a Control Interval 29
  30. 30. Control Information Field of a CI• CIF consists of two subfields:• Control Information Definition Field (CIDF) – It is a 4 byte field – Contains the Offset and Amount of Free space• Record Definition Field (RDF) – It is a 3-byte field. – Length of records (based on the spread of data) – Number of adjacent records that are of same length 31
  31. 31. Control Information Fields in a CIRecord Type Number of Records/CI Control Information (bytes)Fixed Length Multiple 10Fixed Length 1 7Variable Length Depends on the spread 4 (CIDF) and 3 (RDF) of records 32
  32. 32. Format of Index Control Interval• Header Entry1 Entry2 Entryn CIF KSDS Control Interval Control Information Field 33
  33. 33. Structure of VSAM Datasets Session 2 • 34
  34. 34. Topics Covered• Types of VSAM Datasets• More on KSDS Index Structure 35
  35. 35. Objective• Understand the types and internal organization of VSAM datasets• Identify appropriate applications for VSAM data sets• Understand KSDS Index Search Techniques 36
  36. 36. Types of VSAM Datasets • 37
  37. 37. VSAM Datasets Types• Entry Sequenced Data Set (ESDS)• Relative Record Data Set (RRDS)• Key Sequenced Data Set (KSDS)• Variable Length Relative Record Data Set (VRRDS)• Linear Data Set (LDS) 38
  38. 38. ESDS CA Structure• 39
  40. 40. RRDS Structure 41
  41. 41. COBOL example - Sequential Retrieval • SELECT <vsamfile> • ASSIGN TO <ddname> • ORGANIZATION IS RELATIVE • ACCESS IS SEQUENTIAL • RELATIVE KEY IS RR-NUMBER 42
  42. 42. COBOL example - Direct Retrieval• SELECT <vsamfile>• ASSIGN TO <ddname>• ORGANIZATION IS RELATIVE• ACCESS IS RANDOM• RELATIVE KEY IS RR-NUMBER. 43
  43. 43. KSDS Structure• 44
  46. 46. LDS Structure 47
  47. 47. Comparison of VSAM DS• 48
  48. 48. Comparison of VSAM DS (Contd.)• 49
  49. 49. More on KSDS Index Structure • 50
  50. 50. KSDS Structure 51
  51. 51. General Format of Index Set 52
  52. 52. General format of Sequence Set 53
  53. 53. Index Search Techniques• Horizontal Search – For a Sequential Search, search is performed with the key value less than or equal to the sequence set record• Vertical Search – For a Random Access, search is performed from the Index set – Once the key <= condition is met, then it follows a downward pointer to the corresponding Sequence set 54
  54. 54. Example-1How Index & Sequence Sets work 55
  55. 55. Example-2Data Component Structure Data Records 56
  56. 56. Example-2 (Contd.) Data Component Structure Index Set Record 57
  57. 57. Share option in VSAM• Share option in VSAM is defined asConcurrent Usage of Dataset by several People at thesame time. We can use this option for sharing thefiles in the same region and in other system. TheSHAREOPTION has two parameters, the inter-systemparameter and intra-system parameter.• Syntax:SHAREOPTIONS(crossregion,crossystem) 58
  58. 58. Share option cont:....• If the source data set is allocated with DISP=SHR, there is arisk that it could be updated by a region other than the FOR. If thishappened, the data table would no longer match the source data set. Tominimize this risk, the VSAM cross-region SHAREOPTION should be setto 1 or 2.• 1 means that either one region can have update access to thedata set or many regions can have read-only access.• 2 means that one region can have update access to the dataset and, at the same time, many regions can have read-only access.• Regardless of the setting of DISP, a warning message is issued if thecross-region SHAREOPTION is 3 or 4, or if it is 2 but the CICS-maintaineddata table has read-only access (which means another region might beable to update the data set). 59
  59. 59. Syntax and attributes 60
  60. 60. Access Method Services Session 3 • 61
  61. 61. Topics Covered• Introduction to IDCAMS• IDCAMS Commands• Define and Load a VSAM dataset• VSAM Advanced Topics 62
  62. 62. Objectives• Use Access Method Services (AMS )• Identify some useful AMS Commands• Define and Load a Basic Cluster with IDCAMS• Define and Build Alternate Index 63
  63. 63. Introduction to IDCAMS • 64
  64. 64. IDCAMS Utility• Multifunction utility program supplied with VSAM (IDCAMS) to manage and maintain datasets 65
  65. 65. IDCAMS Features• IDCAMS can be used to – Define, Alter and Delete datasets and allocate space for them – List and Maintain VSAM Catalogs – Load, Print and Copy datasets – Reorganize datasets – Define and build alternate indexes – Facilitate backup and recovery – Provide security and integrity functions 66
  66. 66. Invoking IDCAMS 1. As a Job or Job step • Example• //YOURJOB JOB (ACCT),IDCAMS JOB,• //STEP1 EXEC PGM=IDCAMS• //SYSPRINT DD SYSOUT=*• //SYSIN DD *• AMS commands and their parameters• /* 67
  67. 67. Invoking IDCAMS (Contd.)• 2. TSO can be used with VSAM and access method services to – Execute access method services commands – Execute a program to call access method services3. From an application Program 68
  68. 68. IDCAMS Commands • 69
  69. 69. COMMANDS• Modal Commands – Used to control execution and establish options – Modal commands allow the conditional execution of functional commands.• Functional Commands – Used to invoke access method services 70
  70. 70. COMMANDS (Contd..1)• COMMAND specifies the type of service requested• Default statement margins are positions 2 through 72.• Command stmt can be continued to the next line with ‘-’ as the last parameter• Comment may be embedded in Command statements between /* and */ 71
  71. 71. COMMANDS (Contd..2) 72
  72. 72. Condition Codes• IDCAMS returns a condition code following the execution of each Command• Can be used to selectively execute or skip subsequent commands• Initialized to zero at the start of the execution 73
  73. 73. Condition Codes (Contd..1)• LASTCC - specifies the condition code value that resulted from the immediately preceding function command• MAXCC - specifies the maximum condition code value that has been established by any previous function command 74
  74. 74. Condition Codes (Contd..2)• Code Explanation• 0 Function executed successfully• 4 Some problem was met in executing the function but it was possible to continue. The continuation might not provide• exact results, but no permanent harm will have been done 75
  75. 75. Condition Codes (Contd..3)• Code Explanation• 8 A requested function was completed but major specifications were unavoidably bypassed• 12 The requested function could not be performed, as a result of a logical error• 16 A severe error occurred that caused the Job Step to terminate 76
  76. 76. Modal Commands• IF-THEN-ELSE : – Used to control command execution on the basis of condition codes• DO-END : – Used to specify the group of commands as a single unit 77
  77. 77. Modal Commands (Contd.)• NULL : Used to indicate that no action is to be taken• PARM : Specifies processing options to be used during execution• SET : Used to change or reset a previously defined condition code 78
  78. 78. Modal Commands - Syntax• IF {LASTCC|MAXCC} {operator} {numeric value}• THEN {command }• DO• {command set}• END• ELSE {command}• DO• {command set}• END 79
  79. 79. Functional Commands• DEFINE Used to define the following objects – Alias – Alternate index – Cluster – Dataspace – User Catalog and Master Catalog – Path – Catalog entry for a Generation Data Group – Catalog entry for a non-VSAM dataset 80
  80. 80. Functional Commands (Contd..1)• DELETE Used to delete catalogs, VSAM and non-VSAM datasets• EXAMINE Analyzes and reports on the structural consistency of the index component and/or data component of KSDS cluster• LISTCAT Used to list catalog entries 81
  81. 81. Functional Commands (Contd..2)• IMPORT Connects user catalogs and imports VSAM datasets• EXPORT Disconnects user catalogs and exports VSAM datasets.• PRINT Used to print VSAM and non-VSAM datasets and catalogs 82
  82. 82. Functional Commands (Contd..3)• ALTER - Used to alter attributes of datasets and catalog that have already been defined• Alter – Freespace – Volume – Prevent temporary updates to a VSAM dataset 83
  83. 83. Functional Commands (Contd..4)• BLDINDEX - Builds alternate indexes for existing datasets• Keys will be actually built from the base cluster with the BLDINDEX command• VERIFY : Used to cause a catalog to correctly reflect the end of a dataset after an error occurred in closing a VSAM dataset. The error may have caused the catalog to be incorrect. 84
  84. 84. Functional Commands (Contd..5)• REPRO• Loads an empty VSAM cluster with records• Creates backup of a VSAM dataset on a sequential dataset and restores the dataset• Merges data from two VSAM datasets 85
  85. 85. Example: Modal & Functional Commands• //JOBNAME JOB ...• //STEP1 EXEC PGM=IDCAMS• //SYSPRINT DD SYSOUT=*• //SYSIN DD *• DEFINE CLUSTER -• IF LASTCC = 0 THEN -• REPRO -• ELSE -• DO• SET LASTCC = 0• DELETE CLUSTER ...• DEFINE CLUSTER ...• END• /* 86
  86. 86. Define and Load a VSAM Dataset • 87
  87. 87. DEFINE CLUSTER• The DEFINE CLUSTER command can be used to define a cluster and specify attributes for the cluster as a whole and for the components of the cluster. The general format is : 88
  88. 88. LISTCAT• The LISTCAT command lists catalog entries. – Freespace, CI/CA split, Data Attributes, Statistics. Allocation information• All parameters of the LISTCAT command are optional• LISTCAT can be used under TSO 89
  89. 89. LISTCAT Syntax• LISTCAT ALIAS | ALTERNATEINDEX |• CLUSTER | NONVSAM | PATH | ENTRIES(entryname/password entryname/password..) |• LEVEL(level)• EXPIRATION(days)• NAME | HISTORY | VOLUME|• ALLOCATION | ALL• OUTFILE(ddname) 90
  90. 90. REPRO• The REPRO command copies VSAM and non- VSAM data sets, copies catalogs. 91
  91. 91. REPRO Syntax• REPRO {INFILE(ddname)/password• INDATASET(entryname)/password• {OUTFILLE(ddname/password• OUTDATASET(entryname/password}• ( CHARACTER | DUMP | HEX )• ( FROMKEY(key) |• ( FROMADDRESS(address) |• ( FROMNUMBER(number) )• SKIP(number)• ( TOKEY(key) |• TOADDRESS(address) |• TONUMBER(number) )• COUNT(Number) 92
  92. 92. DELETE• The DELETE command deletes catalogs, VSAM datasets, non-VSAM datasets and objects. 93
  93. 93. DELETE Command Syntax• DELETE (entryname/password entryname/password..)• ALIAS | ALTERNATEINDEX | CLUSTER | NONVSAM |• PATH | USERCATALOG• ERASE | NOERASE• PURGE| NOPURGE• FORCE | NOFORCE 94
  94. 94. PRINT• PRINT: The PRINT command prints VSAM datasets, non-VSAM datasets, and catalogs. The syntax is: 95
  95. 95. PRINT Syntax• PRINT {INFILE(ddname /password )• INDATASET(entryname /password ) }• CHARACTER| DUMP | HEX• FROMKEY(key) |• FROMADDRESS(address) |• FROMNUMBER(number) }• SKIP(number)• OUTFILE(ddname)• TOKEY(key) |• TOADDRESS(address) |• TONUMBER(number)|• COUNT(Number) 96
  96. 96. VERIFY• The VERIFY command causes a catalog to correctly reflect the end of a VSAM data set after an error occurs while closing a VSAM data set• The syntax is: VERIFY {FILE(ddname/password) | DATASET(entryname/password)} 97
  97. 97. VERIFY Example• Example of a typical VERIFY usage• Job TRGJJJJ has terminated abnormally and VSAM dataset TRGXXX.MAST.CLUSTER is not closed correctly. This job is followed by another job that uses this file for an IDCAMS copy. Following are the set of return codes that will appear in the Job Spool• In JESMSGLG the error will be IEC161I 056-084,TRGGXXXX,JS010,IFILE01,,,• In SYSPRINT of the step failed the error will be IDC3300I ERROR OPENING TRGXX.MAST.CLUSTER IDC3351I ** VSAM OPEN RETURN CODE IS 118• Solution: A VERIFY issued on VSAM file TRGXXX.MAST.CLUSTER will correct this error 98
  98. 98. ALTERNATE INDEX• Allows for a KSDS to be accessed in a different order other than the primary key• Allows the creation of an index for a non- indexed object, such as an ESDS cluster 99
  99. 99. Steps to create an ALTINDX• DEFINE command to create the alternate index• BLDINDEX command to build the keys for the alternate index• DEFINE command to create a PATH relating the alternate index to the base cluster 100
  100. 100. BLDINDX• The BLDINDEX command builds alternate indexes for existing data sets• Alternate Index can be built only after its base has been loaded with at least one record 101
  101. 101. DEFINE PATH• After defining an alternative index, a PATH must be defined to access the data set. This forms the connection between the alternative index and the base cluster, and the connection is stored in the catalog• When a program opens a path for processing, both the base cluster and the alternate index are opened 102
  102. 102. GDG• A group of chronologically or functionally related data sets are called Generation Data Group (GDG)• Each data set within a GDG is called a Generation Data Set or simply a Generation• They are processed periodically, often by adding a new generation, retaining previous generations, and sometimes discarding the oldest generation• Each generation data set in the group will have the name as GDG name.GxxxxVyy, where “xxxx” is the generation number and “yy” is the version number 103
  103. 103. GDG (Contd..)• GDGs can be referred in a JCL by means of an absolute name or relative name• Absolute name is by coding the complete Generation name as GDGname.G0001V00• Relative name is a signed integer used to refer to the latest (0), the next to the latest (−1), and so forth, generation. The relative number can also be used to catalog a new generation (+1) 104
  104. 104. GDG Advantages• The advantages of grouping related data sets are: – All of the data sets in the group can be referred to by a common name – The operating system is able to keep the generations in chronological order – Outdated or obsolete generations can be automatically deleted by the operating system 105
  105. 105. GDG Usage• One of the important usage of a GDG is for cataloging periodic backups of VSAM datasets – Example, a GDG of limit 7 can be used to take backup of VSAM data sets from the batch job for all 7 days of the week – The GDG base after data sets are cataloged will be as follows • GDGname.G0001V00 • GDGname.G0001V01 • ……………………… • GDGname.G0001V06• Another important usage of GDG is for cataloging periodic reports (weekly, monthly, etc). Example, a GDG with limit 12 can hold monthly reports for a year 106
  106. 106. GDG Syntax• DEFINE GENERATIONDATAGROUP (NAME(entryname) LIMIT(limit) [EMPTY | NOEMPTY] [SCRATCH | NOSCRATCH] [TO(date) | FOR(days)]) 107
  107. 107. Utility U.5 in ISPF• A user interface is available under option U.5. This provides 2 options – Access method services – VSAM maintenance utility 108
  108. 108. U.5.1 Option• Access method services (option u.5.1) provides• interface for the following functions – Define Cluster – Define alternate index – Define path – Alter VSAM dataset characteristics – Rename a dataset – Copy/Load a VSAM dataset – Delete a VSAM dataset – Print a VSAM dataset – Verify endfile markers 109
  109. 109. VSAM Advanced Topics • 110
  110. 110. CICS VSAM Transparency for z/OS• CICS VSAM Transparency for z/OS can help you unlock value in data used by your legacy applications and extend its use to new DB2 applications, online and e-business 111
  111. 111. VSAM to DB2 migration• 24x7 availability• Running adhoc queries• Ability to perform data analysis (mgt reporting, analytics)• Exploitation of database maintenance tools• Integration with new applications based on DB2 technology 112
  112. 112. Other advanced topics in VSAM• VSAM Extended Format & Extended Addressability• Data striping• Data compression• Partial space release• System-managed buffering (SMB)• VSAM Record Level Sharing (RLS)• Utilities: File-Aid, DITTO, STARTOOL 113
  113. 113. THANK YOU 114