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.

VSAM Introduction

An ACCESS METHOD is a component of the operating system.

It is an interface between the application program and the physical operation of storage devices.

Requirement of an Access Method

– Applicability to batch and on-line processing.

– Applicability to different types of access.

– Central control over creation, access and deletion of data.

– Independence from type of storage devices.

– Ability to move the same data to a different operating system ( cross Region & Cross System)

Earlier Access Methods

Access Methods are of two categories: BASIC and QUEUED

– Basic access methods provide the most low-level services for accessing datasets.

Examples of Basic Access Methods are :

– BSAM: Basic Sequential Access Method (for sequential datasets).

– BISAM: Basic Indexed Sequential Access Method (for indexed sequential datasets)

– BDAM: Basic Direct Access Method (for direct access datasets)

Queued access methods provide greater efficiency for sequential access of sequential and indexed sequential datasets.

– When new records are added, a new storage location is calculated. This leads to large gaps between records.

– Space used by a deleted record cannot be recovered unless the file is reorganized.

Examples of Queued Access Methods are:

– QSAM : Queued Sequential Access Method (for sequential datasets)

– QISAM : Queued Indexed Sequential Access Method (for indexed sequential datasets)

– There are no queued access methods for direct datasets.

Features of VSAM

VSAM (Virtual Storage Access Method) is a high-performance access method used in mainframe operating systems like OS/VS1, MVS, MVS/XA, DOS/VS etc.

VSAM makes efficient use of the virtual storage of MVS. Hence the name Virtual Storage Access Method.

VSAM can only manipulate data that resides on a DASD (Direct Access Storage Device).

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

Data retrieval is faster because of an efficiently organized index. The index is small because it uses a key compression algorithm.

Insertion of records is easy due to embedded free space in the cluster. However, the free space causes datasets to require more space on the disk.

Records can be physically deleted and space occupied by them can be reused without any reorganization.

VSAM datasets can be shared across regions and systems.

Access Method Services (AMS) commands can be executed as TSO commands.

Batch and On-line processing is supported.

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.

Datasets can be physically distributed over various volumes based on key ranges

IDCAMS commands can be included in JCL to handle VSAM datasets

Disadvantages of VSAM

To allow easy manipulation of records in a dataset, free space must be left in the dataset. This increases the disk space required. However no free space is required for datasets used for read-only purposes.

Integrity of VSAM datasets in cross-region and cross-system sharing must be controlled by the user.

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 b

ased on the way records are stored and accessed.

ESDS Entry Sequenced dataset.

In an ESDS, records are stored in the order in which they were entered.

New records are always added at the end of the dataset (Append).

Records can be of Fixed or Variable length.

Records can be accessed sequentially because An ESDS has no unique key-field.

Random access is possible using the Relative Byte Address (RBA) of the record. The RBA of the record is the number of bytes in the file before the beginning of that record.

Records can be updated in place but the record length cannot be changed.

Records cannot be physically deleted.

Physically an ESDS is stored as only one component.

RRDS Relative record dataset.

An RRDS is a series of continuous fixed-length slots. Each slot may or may not contain a record. Each slot is identified by its position relative to the first slot in the dataset.

This relative position is called the Relative Record Number (RRN) of the slot.

RRDS records can be inserted, retrieved, updated and deleted and Records can be accessed sequentially and randomly.

RRDS records are of fixed length. When a record is deleted, the slot remains empty till a new record is inserted in it. The new record will have the same RRN as the record deleted.

RRDS is not suitable for applications which leave many slots empty as this wastes storage space.

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.

LDS Linear dataset.

An LDS has no logical record structure. It does not contain control information required by VSAM to organize a dataset into logical records.

The absence of such control information allows very high access speed It is mostly used by DB2.

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 introducted 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.

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.

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

ICF ( Integrated Catalog Facility)

The relatively permanent and temporary parts of the information are stored separately.

The part of the catalog storing stable information is called the Basic Catalog Structure (BCS). It was physically stored as a single KSDS and the volatile information is stored in several VVDS (VSAM Volume DataSets).

Each volume having VSAM datasets has a VVDS on it. A VVDS is physically an ESDS. A VVDS has a standard name: SYS1.VVDS.Vxxx where xxx is the volume label of that volume.

Vsam records

VSAM records can be fixed or variable length. Records can also be spanned across the CI.

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.

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.

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 block size 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. Up to 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 ie. During DEFINE CLUSTER command.

CI is the unit of data that is actually transmitted when records are read / written

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

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

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.

Figure 3.2 Contents of Control Field

Control Interval Descriptor Field (CIDF) which is of 4bytes 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 RDF’s 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.

Control Areas

Control Area is a fixed length unit of contiguous DASD storage. Control Area consists of many Control Intervals and is VSAM’s internal unit for allocating space within a cluster.

The Control Area size can vary from one track to one cylinder depending on unit of allocation. There is no way a Control Area size can be defined. VSAM computes it internally.

CONTROL AREA

Figure 3.3 Control Area

Spanned Records

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.

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.

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 below

Contents of Control Area

KSDS Structure

Index Set

Sequence Set

Figure 3.6 Contents of KSDS Index

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

CI CI CI CI

Contents of Sequence Set

Index Set

Index

component

Sequence Set Sequence Set

CA1 CA2

Figure 3.7 Contents of Index Set

Inserting a new record into a KSDS

Before Control Interval Split

New

Record

Full

Control Interval

Inserting a new record into a full CI

After Control Interval Split

Sequence Set

100

200

Effect of Control Interval Split on Sequence Set

100

200

Effect of Control Interval split on Sequence Set

4. IDCAMS COMMANDS

You can write IDCAMS utility program

To create VSAM dataset

To list, examine, print, tune, backup, and export / import VSAM datasets.

The IDCAMS utility can be in

voked 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.

· DEFINE

· MODAL COMMANDS

Ø IF

Ø SET

Ø PARM

· BUILDINDEX

· REPRO

· PRINT

PATH

· DELETE

· VERIFY

· IMPORT/EXPORT

· ALTER

· LISTCAT

The example 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

//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

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 given below DEFINE is the verb CLUSTER is the object which takes a dataset KASSHKU.KSDS.CLUSTER as parameter

DEFINE CLUSTER -

NAME(KASSHKU.KSDS.CLUSTER) -

CYL/TRK/BYTE(5, 1) -

VOLUMES (BS3013) -

INDEXED -

)

Creating a cluster

Comments:

Comments in IDCAMS can be specified in the following manner

/* comment */

/* -----

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 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.

IDCAMS

Syntax of IF statement

IF LASTCC/MAXCC

comparand VALUE -

THEN -

command

ELSE

Command

Operator(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 -

/* COMMENT */

Command

END

ELSE

Command

JCL using MAXCC and LASTCC

DEFINE CLUSTER

….

IF LASTCC > 0 THEN

SET MAXCC = 16

ELSE

REPRO

……

JCL using MAXCC and LASTCC

DEFINING ESDS CLUSTER

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 (kASSHKU.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=KASSHKU.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.

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. If Multiple volumes, then it 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 AVE 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)

AVE: 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), NONINDEXED(ESDS), NUMBERED(RRDS), LINEAR(LDS).

Format : INDEXED| NONINDEXED | NUMBERED | LINEAR

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

//KASSHKU JOB LA2719, SATYA,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(KASSHKU.ESDS.CLUSTER) - NONINDEXED - RECORDSIZE(125 125) - NONSPANNED - VOLUMES (BLR01) - REUSE ) - DATA(NAME(KASSHKU.ESDS.DATA))

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

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, SATYA,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) - NONSPANNED - VOLUMES (BS3013) - NOREUSE ) -

DATA(NAME(DA0001T.LIB.KSDS.DATA)) -

INDEX(NAME(DA0001T.LIB.KSDS.INDEX))

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)

%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 it 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.

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)

CROSS REGION 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.

CROSS SYSTEM 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)

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 -

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

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

Figure 5.1 HURBA and HARBA

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)

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:

Figure 6.1 Contents of KSDS unique alternate index

For example if a 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:-

Avgerage 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

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 -

)

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.

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

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

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.

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)

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 )

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

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

//DA0001TA JOB LA1279,SATYA,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,SATYA,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

8.VERIFY , PRINT, DELETE, ALTER Command

VERIFY

Verify - preserves data integrity (HURBA)

Format :

VERIFY FILE(ddname/passwd)

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

//DA0001TA JOB LA2179,SATYA,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,SATYA,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

change names

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

Format :

ALTER entryname/passwd 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

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).

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

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.

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

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.

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

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

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.

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

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 :

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.

VSAM Tutorial | Learn VSAM

Requirement of an Access Method

Earlier Access Methods

Access Methods are of two categories: BASIC and QUEUED

– Basic access methods provide the most low-level services for accessing datasets.

Examples of Basic Access Methods are :

– BSAM: Basic Sequential Access Method (for sequential datasets).

– BISAM: Basic Indexed Sequential Access Method (for indexed sequential datasets)

– BDAM: Basic Direct Access Method (for direct access datasets)

Queued access methods provide greater efficiency for sequential access of sequential and indexed sequential datasets.

– When new records are added, a new storage location is calculated. This leads to large gaps between records.

– Space used by a deleted record cannot be recovered unless the file is reorganized.

Examples of Queued Access Methods are:

– QSAM : Queued Sequential Access Method (for sequential datasets)

– QISAM : Queued Indexed Sequential Access Method (for indexed sequential datasets)

– There are no queued access methods for direct datasets.

Features of VSAM

Advantages of VSAM

To allow easy manipulation of records in a dataset, free space must be left in the dataset. This increases the disk space required. However no free space is required for datasets used for read-only purposes.

Integrity of VSAM datasets in cross-region and cross-system sharing must be controlled by the user.

Types of VSAM Datasets

Clusters

ICF ( Integrated Catalog Facility)

Vsam records

SPANNED RECORDS

ESDS

Index Set Sequence Set

4. IDCAMS COMMANDS

· DEFINE

· MODAL COMMANDS

Ø IF

Ø SET

Ø PARM

· BUILDINDEX

· REPRO

· PRINT

· DELETE

· VERIFY

· IMPORT/EXPORT

· ALTER

· LISTCAT

Comments:

Condition code:

IDCAMS

DEFINING ESDS CLUSTER

DEFINE CLUSTER

The NAME parameter

Rules for Naming Cluster

The SPACE Allocation parameter

Format :

The VOLUMES parameter

Format :

Example :

The RECORDSIZE parameter

This parameter tells VSAM what size records to expect. The AVE 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 :

Note :

The SPANNED parameter

The DATASET-TYPE parameter

Defining KSDS Cluster

The DATA parameter

The INDEX parameter

Format :

The KEYS parameter

Format :

Example :

The FREESPACE parameter

Example : FREESPACE(20 10)

The REUSE parameter

The CONTROL INTERVAL SIZE parameter

Format :

Example :

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

SHAREOPTIONS

Format :

5. LISTCAT

Format 1:

Examples:

Format 2:

Index Set

Sequence Set