VSAM-handout

Mainframe VSAM

CHAPTER - 1: Introduction to VSAM

Virtual Storage Access Method - VSAM - is a data management system introduced by IBM in the 1970s as part of the OS/VS1 and OS/VS2 operating systems. Although there are still datasets that are best managed with the several other (non-VSAM) data management methods, VSAM is a major component of modern IBM operating systems. VSAM is a high performance access method used to organize data and to maintain information about that data in an index or library called a catalog.

VSAM acts as interface between Operating System and Application Program. VSAM is an access method used to organize data and maintain information about the data in a catalog.

All VSAM data sets reside on DASD Devices and must be defined in a catalog.

There are two major parts to VSAM:

Catalog management

Record management

Catalog Management

The catalog contains information about the VSAM data sets. The catalog can be an ICF Catalog or a VSAM catalog (older versions of the operating system). DFSMS/MVS deals only with ICF catalogs.

All VSAM data set information is maintained in the ICF catalog and it can be easily retrieved using AMS commands (Access Method Services).

Record management

The purpose of record management is to maintain records in a VSAM data set for an application or a system program. VSAM supports five data set organizations:

Key-sequenced data set (KSDS)

Entry-sequenced data set (ESDS)

Fixed-length relative record data set (RRDS)

Variable-length relative record data set (VRRDS)

Linear data set (LDS)

The primary difference between the VSAM data set organizations is in the way the records are stored and accessed.

VSAM HISTORY

In the year 1973 VSAM was introduced with ESDS & KSDS only and in the year 1975 the concept of Alternate Index, RRDS, and Catalog Recovery features were introduced. VSAM was re-introduced with a facility called as Integrated Catalog Facility (ICF). In the year 1983 VSAM was introduced with DFP/VSAM (Data Facility Product) which can run under MCS/XA. Later in the year 1987 the DFP/VSAM 2.3 with LDS facility was introduced and another VSAM 3.1 under MVS/ESA with DFSMS (Data Facility Storage Management System). In the year 1991, VSAM 3.3 was introduced with variable length records for RRDS

STRUCTURE OF VSAM

iFrames Technologies 1

Mainframe VSAM

VSAM provides a comprehensive catalog facility that stores information about VSAM data sets and other files.

There are two types of catalogs:

Master Catalogs

User Catalogs

Master Catalog

Every system that uses VSAM has one, and only one, master catalog. The master catalog contains entries about system datasets and VSAM structures used to manage the operation of VSAM. The master catalog is created during the System Generation process and usually resides on the System Residence volume. The master catalog "owns" all other VSAM resources in a computer system, and this is denoted by the position of the master catalog.

User Catalogs

A user catalog is a catalog created to contain entries about application specific datasets. The information defining a user catalog is stored into a catalog entry in the master catalog. A production system might have any number of user catalogs, with the datasets cataloged in a specific user catalog related by application type.

ADVANTAGES & DISADVANTAGES OF VSAM

Advantages:

The retrieval of records is faster because of an efficiently organized index. The index is small because of a key compression algorithm used to store and retrieve its records.

Imbedded free space makes the insertion of records easy, and data sets therefore require less reorganization.

The deletion of records in VSAM, unlike that in ISAM, means that they are physically deleted, thus allowing the reclaiming of free space within the data set.

VSAM data sets are device-independent.

VSAM catalogs and data sets are portable between operating systems.

Records can be accessed randomly by key or by address and can also be accessed sequentially at the same time.

Disadvantages:

To take advantage of the partial self-reorganization capabilities of VSAM data sets, free space must deliberately be left. For data sets that are used for read only purposes, no free space is required.

Except for read-only data sets, the integrity of VSAM data sets in cross-system and cross –region sharing must be controlled by the user. Data integrity must be a prime consideration in the initial design of applications that will be shared across systems.

MAJOR AREAS WHERE VSAM IS USED

It can be used as a stand-alone product. VSAM data sets can be created and processed by a powerful software product called IDCAMS.


Mainframe VSAM

Batch application programs in COBOL, PL/I, Assembler, etc. can access VSAM data sets.

In data set management, PDS directories, catalogs, and generation data groups can be manipulated through specific IDCAMS commands. GDGs and catalogs are themselves VSAM data sets, Also, the IDCAMS utility can be used to process older, non-VSAM data set organizations.

Many major IBM software products, such as CICS, IMS, DB2 and TSO, use VSAM data sets in a majority of applications. In some of them, VSAM data sets are the only ones that are compatible.

VSAM is available under all IBM’s Mainframe operating systems; MVS, VM, and VSE. The MVS implementation of VSAM is the most comprehensive. Also, VSAM data sets can be stored on almost all standard disk drives, such as 3390, 3380, 3350, 3370, etc. Present and future mainframe software released by IBM will be designed to process records storage in VSAM data sets. VSAM is going to be around for a long time to come.

VSAM TERMINOLOGY

Before we discuss VSAM data set organizations in detail, we need to review some terms that will be used throughout the book.

Logical record

Control interval

Control area

Logical record (LR)

A logical record is a unit of information used to store data in a VSAM data set. Logical records in VSAM data sets are stored differently than logical records in non-VSAM data sets.

A LR is comparable to the logical-record –length (lrecl) for a Non-Vsam dataset, as in the DCB Parameter of JCL.

Control Interval (CI)

Logical records are contained in a control interval (CI). A group of LRs will make one CI.

The fundamental building block of every component of a VSAM data set is the control interval. A control interval is the unit of information that VSAM transfers between the storage device and the virtual storage. One CI can be made of one or more physical blocks of DASD.


LR

LR LR LR LR

Mainframe VSAM

A CI consists

Logical records stored from beginning to end

Unused space, referred to as free space, for data records to be inserted into or lengthened

The maximum size of a CI is 32k and the minimum size is 512 bytes.

Control information, which is made up of two types of fields; one Control Interval Definition Field (CIDF) per CI, and one or more Record Definition Fields (RDF) per logical record.

1. CIDF is a 4-byte field. It contains information about the length of data in the CI and the amount and location of free space.

2. RDF is a 3-byte field. It describes the length of records and how many adjacent records are of the same length.

Control area (CA)

A control area (CA) is one or more CIs put together into fixed-length contiguous areas of DASD. A VSAM data set is composed of one or more CAs.

The number of CIs in a CA is fixed by VSAM. The CA size is implicitly defined when you specify the size of a data set at data set definition.

The maximum size of a CA is one cylinder and the minimum size is one track.


Control Interval Format for a Non- LDS Cluster.

RDF1

RDF2

RECORD 1 RECORD 2

Logical Record Area

Free space Area

Control Interval

Definition field

Recorddefinitionfield

Mainframe VSAM

Figure 1-2 shows the structure of a CA.

REVIEW QUESTIONS

1. What is VSAM?

2. What are the major parts in VSAM?

3. What are the two Catalogs available in VSAM?

4. What is Control Interval?

5. What is Control Area?

6. How many Bytes occupied for RDF and CIDF?

7. The Maximum and minimum size of a Control Area is __________, _________.

8. What are the advantages and disadvantages of VSAM?

9. What are the different datasets supported by VSAM?

10. What is a logical record?

11. What's the biggest disadvantage of using a VSAM dataset?

CHAPTER --- 2 : Dataset Organization


LR1 LR2 FREE SPACE RDF2 RDF1 CIDF

LR3 LR4

LR5 LR6 FREE SPACE

FREE SPACE RDF4 RDF1 CIDF

RDF RDF CIDF

CA1

CA2

CA3

CA 1

Mainframe VSAM

VSAM DATASET ORGANIZATION

Whenever a record is retrieved from DASD, the entire CI containing the record is read into a VSAM I/O buffer in virtual storage. From the VSAM buffer, the desired record is transferred to a user defined buffer or work area.

The physical organization of VSAM data sets differs considerably from those used by other access methods. VSAM data sets are held in control intervals and control areas; the size of these is normally determined by the access method, and the way in which they are used is not visible to you.

TYPES OF DATASET ORGANISATION

VSAM supports 5 different organizations. They are as follows:

Linear Data Set – LDS – with no record organization

Entry-Sequenced Data Set – ESDS - is like a standard sequential data set.

Fixed-length Relative-Record Data Set - FRRDS - Fixed length RRDS

Variable-length Relative Record Data Set - VRRDS - Variable length RRDS

Key-Sequenced Data Set – KSDS- is like an indexed sequential access method file.

The VSAM data set organizations are superior to the native access methods. VSAM provides for alternate indexes, a feature not available in native access methods. It has an admirable catalog facility that stores more information about VSAM and other data sets. The powerful AMS utility in VSAM provides a variety of services dealing with catalogs, files, security, file management, etc. It provides comprehensive support for application development in many environments such as COBOL, PL/I, FORTRAN, Assembler and CICS.

LINEAR DATA SET (LDS)


WORK AREA

CI

LR1 LR2 LR3

LR2

Mainframe VSAM

A linear data set (LDS) contains data that can be accessed as byte-addressable strings in virtual storage. It is a VSAM data set with a control interval size of 4096 bytes.

An LDS has no imbedded control information in its CI, which is, no RDFs and CIDFs. All LDS bytes are data bytes. Logical records must be blocked and de blocked by the application program, but records do not exist from the point of view of VSAM. An LDS contains a data component only.

LDS are generally used for fast random access to data that has no hierarchical structure - i.e., for data, that is a large flat file, such as a table or array. A relational database is just this. You specify the LDS organization with the IDCAMS DEFINE command specifying the LINEAR parameter.

ENTRY SEQUENCED DATA SET (ESDS)

An ESDS is a sequential file, in which records are typically retrieved in the order in which they were written to the data set and additions are always made at the end of the file. Each record can be identified by a relative byte address or RBA. Records cannot be physically deleted. Since records in an ESDS are not sequenced on any key field, there is no primary key index component. Imbedded free space is not allocated at the time of allocation of an ESDS, since records are not added to the middle of the file. Records in an ESDS may be of variable length.


DATADATA CA

DATA CA

DATA

DATA

DATA

DATA

DATA

Mainframe VSAM

Records can be updated, but without length change. To change the length of a record, you must either store it at the end of the data set as a new record, or override an existing record of the same length that you have flagged as inactive.

A record can be accessed sequentially or directly by its RBA:

Relative Byte Address (RBA) is the address of a record in a dataset. Records can be accessed sequentially or by relative byte address (RBA).The RBA of the first logical record is 0. The second record has an RBA equal to the length of the first record and so on.

TYPICAL ESDS PROCESSING

Sequential processing:

VSAM automatically retrieves records in stored sequence. Sequential processing can be started from the beginning or somewhere in the middle of a data set. If processing is to begin in the middle of a data set, positioning is necessary before sequential processing can be performed.

Direct processing:

When a record is loaded or added, VSAM indicates its RBA. To retrieve records directly, you must supply the RBA for the record as a search argument. Although an ESDS does not contain an index component, you can build an alternate index to keep track of these RBAs.

Empty spaces in the CI are referred to as unused space because they can never be used.

You specify ESDS organization using the IDCAMS DEFINE command and specifying the NONINDEXED parameter.

RELATIVE RECORD DATASET (RRDS)


RECORD1 RECORD2 RECORD3 RECORD4


UNUSED SPACE

RBA 0

RBA 4096

RBA 8192

CI 1

CI 2

CI 3

Mainframe VSAM

1) FIXED LENGTH RECORDS

In an RRDS the entire data set is a string of fixed length slots. Each slot occupies a fixed position and is identified by its position relative to the first slot of the data set.

The relative position of each slot is called relative record number (RRN). An RRN is an integer that identifies the position of the slot no the value of a particular field within the slot. Each slot of an RRDS may or may not contain a record. Records in an RRDS may be inserted, retrieved, updated, and deleted both sequentially and randomly. Records in an RRDS are always fixed in the length. RRDS has only data component. When a record is deleted from a particular slot, the slot remains in the same physical location although a record does not exist in that slot anymore

You specify the RRDS organization using the IDCAMS DEFINE command with the NUMBERED option.

TYPICAL RRDS PROCESSING

CONTROL AREA 2

SLOT 8

CONTROL AREA 1

Slot8The relative record number can be used as a search argument. The

application program inputs the relative record number of the target record and VSAM








DATA CA

DATA CA

APPLICATIONPROGRAM

GET RECORD 25

CI 29 30 31 32

CI 25 26 27 28 CI 21 22 23 24 CI 17 18 19 20

CI 13 14 15 16 CI 9 10 11 12 CI 5 6 7 8

CI 1 2 3 4

Mainframe VSAM

is able to find its location quickly using an internal algorithm. An RRDS can be processed sequentially, directly or skip-sequentially.

RRDS sequential processing is treated the same way as ESDS sequential processing. Empty slots are automatically skipped by VSAM.

An RRDS can be processed directly by supplying the relative record number as a key. VSAM accesses the appropriate slot and returns the record to the user’s buffer. RRDS direct address processing by supplying the RBA is not supported.

Skip-sequential processing is treated like an RRDS direct processing request, but the position is maintained. Records must be in ascending sequence.

2. VARIABLE RELATIVE RECORD DATA SET (VRRDS)

A VRRDS is similar to a fixed-length RRDS, except that it contains variable-length records. Each record has a unique relative record number, and is placed in ascending relative record number order. Each record is stored and retrieved using its relative record number. VRRDS has no preformatted slots.

The relative record number of a record cannot change. When that record is erased, the relative record number can be reused for a new record.

You can specify free space for inserting records and increasing the length of a record. VRRDS is a KSDS processed as an RRDS, so an index will be created.

You specify the VRRDS organization with the IDCAMS DEFINE command with the NUMBERED option and variable length record.

REVIEW QUESTIONS.

1. Which VSAM cluster support only fixed length records?

a) LDS

b) RRDS

c) ESDS

d) KSDS

2. FREESPACE can be specified for which type of cluster?

a) LDS

b) B. RRDS

c) C. ESDS

d) D. KSDS

3. For a KSDS, the larger the data CA size, the smaller the number of index CIs.

A. TRUE

B. FALSE.

4. VSAM control intervals containing data records have at least one RDF and one

CIDF.


Mainframe VSAM

A. TRUE

B. FALSE

5. In which cluster type are records always added at the end of the data set?

a) LDS

b) RRDS

c) ESDS

d) KSDS

6. Which VSAM clusters support only fixed length records?

a) LDS

b) RRDS

c) ESDS

d) KSDS

7. The types of processing supported by RRDS are

a) sequential

b) skip-sequential

c) direct

d) a and b

e) a, b and c

8. The types of processing supported by ESDS are

a) Sequential

b) skip-sequential

c) Direct

d) a and b

e) a and c

9. What is the Difference between LDS & ESDS?

10. How Many Times Secondary Space Allocated?

11. What is the RRN for the first record in RRDS?

CHAPTER - 3: KSDS

KEY SEQUENCED DATASET (KSDS)


Mainframe VSAM

In a KSDS, records are placed in the data set in ascending collating sequence by key. The records for KSDS can be fixed-length or variable-length records. The key of the record contains a unique value that determines the record's collating position in the data set. The key must be in the same position in each record.

The key data must be contiguous and each record's key must be unique. After it is specified, the value of the key cannot be altered, but the entire record can be deleted. When a new record is added to the data set, it is inserted in its collating sequence by key.

A KSDS has a data and an Index Component. The Index Component keeps track of the used keys and is used by VSAM to retrieve quickly a record from the data component, when a request is made for a record with a certain key. A KSDS can have fixed or variable length records. A KSDS can be accessed either sequentially or directly or skip-sequentially.

You specify the KSDS organization using the IDCAMS DEFINE command with the INDEXED parameter.

DATA / INDEX RELATIONSHIP

A KSDS has an index that relates key values to the relative locations of the logical records in a data set. This index is called the Prime Index. It has two uses:

Locate the collating position when inserting records.

Locate records for retrieval.

When initially loading a data set, records must be presented to VSAM in key sequence. The Index is built automatically by VSAM as the data set is loaded with records. When a data CI is loaded with records, VSAM makes an entry in the index. The entry consists of the highest possible key in the data CI and a pointer to the beginning of that CI.

VSAM index can consists of more than one index level. Each level contains a set of records with entries giving The location of the records in the next lower level.

Sequence Set: contains the index CI’s at the lowest level.

There is one CI in the sequence set for each data CA. It contains pointers and high key information for each CI within the data CA. It contains also horizontal pointers from one sequence set CI to the next sequence set CI.

Index Set: remainder of the index component.


INDEX COMPONENT

DATA COMPONENT

Mainframe VSAM

If there is more than one sequence set level record, VSAM automatically builds another index level. Each CI in the index set contains pointers and high key information for CI’s in the next lower level of the index.

TYPICAL KSDS PROCESSING:

INDEX COMPONENT

DATA COMPONENT


IS1IS2IS3

SS1 SS2 SS3 SS4 SS5

CI1

CI2

CI3

CI1

CI2

CI3

CI1

CI2

CI3

CI1

CI2

CI3

CI1

CI2

CI3

CA5CA4CA3CA2CA1

Index Component

Data Component

Index set

Sequence set

079 236

007 021 079 FS 099 124 236 FS

001 002 004 007

008 012 018 021

067 079

084 087 099

111 124

238

Mainframe VSAM

CONTROL AREAS

There are three methods by which to access a KSDS. These are sequential, direct, or skip-sequential.

Sequential access is used to load a KSDS, and to retrieve, update, add and delete records in an existing data set. Sequential access means that records are retrieved one-by-one, starting from the first record, in the order that they are placed in the dataset.. When retrieving records, you do not need to specify key values because VSAM automatically obtains the next logical record in sequence. The sequence set is used to find the next logical CI. Sequential access allows you to avoid searching the index more than once. Sequential is faster than direct for accessing multiple data records in ascending key order.

Direct access is used to retrieve, update, add and delete records in an existing data set. You need to supply a key value for each record to be processed. You can supply the full key or a generic key. The generic key is the high order portion of a full key. For example, you might want to retrieve all records whose keys begin with XY (where XY is the generic key), regardless of the full key value. VSAM searches the index from the highest-level index set CI to the sequence set for a record to be accessed. Vertical pointers in the sequence set CI are used to access the data CA containing the record. Direct access saves you a lot of overhead by not retrieving the entire data set sequentially to process a small percentage of the total number of records.

Skip-sequential access is used to retrieve, update, add and delete records in an existing data set. In skip-sequential method of access, the record pointer can be placed anywhere within the dataset (by giving the key) and records can then be retrieved sequentially from that point.

LOADING A KSDS:

When loading a KSDS, logical records are stored in ascending key sequence within a data CI. The data component for a KSDS can contain user specified FREESPACE. This free space is used later, when records are inserted or expanded.

CI Free Space: Percentage of CI left empty / unused at load time.

CA Free Space: Percentage of CIs in each data CA empty / unused at load time.


SEQUENCE SET CI

FS407740654037

Mainframe VSAM

UPDATING A KSDS CLUSTER:

Insertion:

While Inserting a Record in the KSDS Cluster, the records are placed in logical sequence. The CI free space is used. The Index Component is not altered.

Deletion:

While deleting a record from the KSDS Cluster, the records are physically removed from CI. The records in CI with higher keys are shifted left and the available free space in the CI is increased. The Index Component is not altered.

INSERT 4058

SEQUENCE SET CI

CI 0

CI 1

DATA CA CI 2

CI 3

CONTROL INTERVAL SPLIT

When inserting a record in the CI, if there is no enough free space in the CI, then the CI will be split as follows:

Half of the full CI is moved to an empty / free CI within same CA. So, CA free space is used.

A new index entry is inserted in the sequence set record.


4012 4023 4034 4037 FREE SPACE

4041 4050 4052 4085 FREE SPACE

4072 4073 4075 4077 FREE SPACE

FREESPACE

CI 0

CI 1

CI 2

CI 3

4037 4065 4077 FS

4012 4023 4034 4037 FREESPACE

4041 4050 4052 4058 4065

FREE SPACE

4072 4073 4075 4077 FREESPACE

Mainframe VSAM

The existing index entry is updated in the sequence set record.

As a result of the CI split, the physical sequence of the data is no longer the same as the logical sequence.

This will be illustrated by the following diagram.

.

INSERT 4046

SEQUENCE SET

CI 0

CI 1

DATA CA

CI 2

CI 3

CONTROL AREA SPLIT

When there are no more free CI s in the CA then VSAM performs a control area split.

o VSAM allocates a new CA at the end of the data component

o Approximately half of the data CI s are moved from the full CA to the

new CA.

o A new sequence set CI is created for the new data CA.

o The old sequence set CI is modified

o The index set is updated. In the given below example a new index set

CI will be created that will be the highest-level index set CI. Then VSAM performs a control Interval split.

This will be illustrated by the following diagram.

TO INSERT 4074


4037 4050 4065 4077

4012 4023 4034 4037 FREE SPACE

4041 4046 4050 FREE SPACE

4072 4073 4075 4077 FREE SPACE

4052 4058 4065 FREE SPACE

Mainframe VSAM

CA1

4076 4077 4075

CA2

SPANNED RECORDS

Spanned records are records with a record size greater than the CI size specified.

Spanned records can only be used in ESDS or KSDS organizations.

Spanned records can “span” control intervals, but not control areas. So, one spanned record is stored in several CI’s.


BEFORE AFTER

4077406540504037

SEQUENCE SET CI INDEX SET CI

40774065

SEQUENCE SET CI

4037 4050 4065 40654040654065

4037403440234012

405040464041

40774076 4073 40754072

406540584052

4074 4077

4037403440234012

4050

40464041

FREE SPACE

406540584052

407440734072

FREE SPACE

FREE SPACE

Mainframe VSAM

As in the above diagram, the spanned record spans three CI’s. The ‘segment’ of the first CI contains part of data along with two RDF’s and one CIDF. The right RDF gives the length of the segment. The left RDF gives the update number of the segment (used to maintain update consistency of all segments during an update).

A CI that contains the record’s segment of a spanned record contains control information. However a new record cannot be inserted into the same CI. As in the diagram, the third CI contains the spanned data, and the rest of the space becomes unused space. A new record would move into the fourth CI.

ACCESSING SPANNED RECORDS

Spanned records must be accessed in MOVE mode. The application program must contain a work area as the largest spanned record in the data set.


RECORD 1

RECORD 1 R R CSEGMENT1 D D I F F D 2 1 F

RECORD 1 R R CSEGMENT2 D D I F F D 2 1 F

RECORD 1 UNUSED R R CSEGMENT3 SPACE D D I F F D 2 1 F

CI 1

CI 2

CI 3

DATA BUFFERS

WORK AREA

ADDRESS SPACE

Mainframe VSAM

REVIEW QUESTIONS:

1. Specifying CISZ (4096) at the cluster level for a KSDS results in

a) VSAM ignoring the specification

b) Data and index CISZ 4k each

c) Data CISZ 4k; index CISZ selected by VSAM

2. What is the use of Free Space in KSDS?

3. How do you define a KSDS?

4. VS COBOL II supports SKIP processing.

a) TRUE

b) FALSE

5. VSAM request macros (e.g., GET, PUT) point to which other macro(s)?

a) OPEN

b) ACB

c) RPL

d) CLOSE

e) (B) and (C)

6. NONSPANNED records may be accessed in either MOVE mode or LOCATE mode.

a) TRUE

b) FALSE

7. What does a file status of 02 on a VSAM indicate?

8. Explain CI split and CA split

CHAPTER - 4: ACCESS METHOD SERVICES (AMS)

One of VSAM’s strength is that a single set of data management facilities called Access Method Service (AMS) manages both VSAM and non-VSAM datasets.

IDCAMS is a general-purpose utility program, used with VSAM, to establish and maintain catalogs and data sets. It provides the services described above, and more.

AMS uses a command processor called IDCAMS to handle a variety of functions such as creating, reproducing, printing datasets and listing catalog contents. These functions of AMS are performed thru functional commands.

A functional command can have one or more parameters that can be positional or keyword. Positional parameters are identified by its position in relation to other parameters: a keyword parameters can be used in any place in relation to other keyword parameters because it is identified by the particular keyword used.

Types of AMS commands

Functional commands

Modal commands

Commonly used AMS commands

AMS command Function

Functional commands

ALTER Changes information specified for a catalog, cluster,


Mainframe VSAM

alternate index, or path at define time.

BLDINDEX Builds an alternate index.

DEFINE ALTERNATE INDEX

Defines an alternate index.

LISTCAT List information about data sets

REPRO Copies records from one file to another. The input and output files can be VSAM or non-VSAM

PRINT Prints the contents of a VSAM or non-VSAM file.

DEFINE CLUSTER Defines a VSAM file, whether it’s KSDS, ESDS, or RRDS

DEFINE MASTER CATALOG

Defines a master catalog

DEFINE PATH Defines a path that relates an alternate index to its base cluster

DEFINE USERCATALOG Defines a user catalog.

DELETE Removes a catalog entry for a catalog, cluster, alternate index or path

EXPORT Produces a transportable file.

IMPORT Copies a previously exported file.


Mainframe VSAM

Modal commands

IF Controls the flow of command execution by testing condition codes returned by functional commands

SET Controls the flow of command execution by altering condition codes returned by functional commands

PARM Sets options values that effect the way AMS executes.

AMS PERFORMANCE PARAMETERS

1) CONTROL INTERVAL SIZE

Syntax : CONTROLINTERVALSIZE (bytes)

Abbr : CISZ or CISIZE

Default : Calculated by VSAM

Control Interval size (CIDF & RDF) & FREESPACE must be taken into account

Thumb Rule for CISIZE

If the record length is <8192, multiples of 512, >=8192, multiples of 2048

2) FREESPACE

Syntax : FREESPACE (CI% CA%)

Default : FREESPACE(0 0)

High Free space results in more I/O & consumes larger DASD space

Very low FREESPACE results in CI splits and degrades performance

Amount of FREESPACE depends on

o Rate of growth of records

o Expected number of records to be deleted

o Reorganization frequency

o Performance consideration

o

o 3) BUFFERSPACE

o Syntax : BUFFERSPACE (bytes)

o Abbr : BUFSP

o Default : Two data buffers plus one additional index buffer for KSDS

o Used to improve Input/output performance

o Can also be specific in JCL EXEC parameter

o

o //DD1 DD DSNAME=ANYVSAM1,

o // AMP=('BUFND=4,BUFNI=4,STRNO=2')

o

o More on VSAM Buffers


Mainframe VSAM

o

Strings (STRNO in AMP parameter)

o Defines number of concurrent access

o For batch processing, a string of 1 is enough

o For online processing more strings is required

Data Buffers (BUFND in AMP parameter)

Random Access

o Minimum of 2 (One for normal access and one for split processing) is required

Sequential Access

o Ideal to process a track

o Allocate number of buffers based on the number of CI/TRK

o For READ add 1 more buffer and for WRITE add 2 more buffers

o Index Buffers (BUFNI in AMP parameter)

o Default of 1 index buffer is enough

Random Access

o Ideal to keep the index set in virtual memory

o Determine the number of levels (using LISTCAT)

o Allocate number of levels + 1 buffer

o

o 4) RECOVERY / SPEED

Mutually Exclusive

RECOVERY allows you to recover if the job initially loading the dataset fails

SPEED is faster, but does not provide restart feature

Default: RECOVERY

5) SPANNED

Syntax :

SPANNED/NONSPANNED

Default:NONSPANNED

Allows large records to span more than one Control Interval

However, the records cannot span across Control areas

RRDS does not support spanned records.

6) KEYRANGES

Syntax : KEYRANGES (Low - Val; High - Val)

Default : None (No range assumed)

Example :


Mainframe VSAM

KEYRANGES ((000001 100000)+

100001 200000))

The Key Ranges correspond to VOLUMES if ORDERED clause is specified.

7) ORDERED

Syntax : ORDERED / UNORDERED

Default: UNORDERED

Goes together with KEYRANGES clause specifies the volume to which the key values should go.

8) REUSE

Syntax : REUSE/NOREUSE

Default : NOREUSE

REUSE specifies that the cluster can be loaded with fresh records with an implicit delete of existing RECORDS

REUSE cannot be used under following circumstances and hence not recommended

When KEYRANGES parameter is coded

When alternate indexed are defined

9) REPLICATE

Directs the VSAM to duplicate each index as many times as it will fit on its assigned track

Applies only to KSDS index component

To reduce rotational delay and to make I/O faster

Syntax : Replicate / No replicate

Default : No replicate

10) VOLUMES

Can specify different volumes for

Data component

Index component

11) IMBED

Directs the VSAM to place the sequence set (the lowest level of index next to the data component) on the first track of the data control area and duplicate it as many times as it will fit. This process will reduce rotational delay because the desired sequence set record is found faster

Default: NO IMBED

Syntax : IMBED / NO IMBED

Note:

IMBED applies to the index component. Hence it is limited to a KSDS.

IMBED places the sequence set CI for a data control area within the control area.

Uses IMBED only with large control area sizes.


Mainframe VSAM

IMBED requires additional DASD space.

IMBED should provide faster access to data.

12) SHARE OPTION

Syntax : SHAREOPTIONS (Cross-region-value Cross-system-Val)

Cross-region : Concurrent data access on a standalone system (ex: TSO&CICS accessing same data)

Cross-system : Data access for multiple computers (Two different computers that are inter-connected)

Default : SHAREOPTIONS (1 3)

Multiple jobs can read only if no update takes place - Complete data integrity

Multiple jobs can read and at the same time one job can update - Write, but not read integrity

Multiple jobs can read & write simultaneously - No integrity

Same as option 3, but refreshes buffer after every read

Share options 1 & 2 are not allowed for cross-system

For cross region sharing, each batch job must have DISP=SHR

For cross system sharing DISP parameter in the JCL is immaterial

13) ERASE / NOERASE

Default : NOERASE

ERASE instructs VSAM to move zeroes to all the bytes once the cluster is deleted.

INVOKING IDCAMS

//MYJOB JOB……………

//STEPA EXEC PGM = IDCAMS

//SYSPRINT DD SYSOUT = *

//SYSIN DD *

DEFINE CLUSTER –

.

.

IDCAMS commands can be processed as a job or job step (by specifying PGM=IDCAMS) on the EXEC card.

BASIC IDCAMS COMMANDS

The following are the commands which will be used with IDCAMS procedure.

BUILDINDEX

DEFINE

IMPORT/EXPORT

LISTCAT

REPRO

VERIFY


Mainframe VSAM

AMS COMMAND SYNTAX

Margins Default to 2&72

Separators BLANK,COMMA

Comments /*----------------*/

Continuation HYPEN, PLUS SIGN

Terminator SEMICOLON or Absence of Continuation mark

There are two possible continuation characters:

The PLUS sign (+): ignores the leading blanks on the next line.

The HYPEN sign (-): doesn’t ignore the leading blanks on the next line.

DEFINE SPECIFICATONS

When defining a VSAM cluster using the DEFINE CLUSTER command, the

following must or can be specified.

The data set name:

The cluster name is required.

Component name(s) is/are optional.

The type of the date set type:

KSDS, ESDS, RRDS, LDS.

The data set attributes:

Record size and control interval size.

For a KSDS: Key information and free space distribution.


COMMAND PARAMETERS TERMINATOR

SERVICEFURTHER END OF COMMANDREQUESTED DESCRIBES COMMAND

Data Set Name

Data Set Type

Space Allocation

Where?

How much?

Data Set Attributes

Mainframe VSAM

BASIC DEFINE COMMAND SYNTAX FOR CLUSTER:

The DEFINE CLUSTER Command

DEFINE CLUSTER ( NAME(entry – name)

[ OWNER(owner – id) ]

[ FOR(days) | TO(date) ]

[ INDEXED | NONINDEXED | NUMBERED ]

[ RECORDSIZE (avg max) ]

[ CISZ(size)]

[ SPANNED | NONSPANNED]

[ KEYS (length offset)]

[ FREESPACE ( ci ca) ]

[ VOLUMES ( vol-ser no..)]

[ FILE (ddname) ]

[ { cylinders /kilobytes/megabytes/tracks/records} (primary secondary)}]

[ UNIQUE | SUBALLOCATION]

[ REUSE | NOUSE]

[ SHAREOPTIONS ( a b)]

[ IMBED | NOIMBED]

[ STORAGECLASS(storage – class)]

[ DATACLASS(data-class)]

[MANAGEMENTCLASS (managementclass)]

[ DATA ( [ NAME (entry – name) ]

[ VOLUMES (vol –ser ….)]

[ FILE (ddname) ]

[ { cylinders/kilobytes/megabytes/tracks/ records} (primary secondary) ] ) ]

[ INDEX ( [ NAME( entry – name) ]

[ VOLUMES ( Vol –ser ….)]

[ { cylinders/kilobytes/megabytes/tracks/ records} (primary secondary) ] ) ]

[CATALOG ( name [/ password]) ]

Explanation

NAME (entry –name) Specifies the name of the cluster or component

OWNER (owner –id) Specifies a 1 to 8 character owner-id.

FOR (days) TO (date) Specifies a retention period ( in the format dddd) or an expiration date (in the format yyddd)

INDEXED / NONINDEXED/NUMBERED Specifies the file organization: SDS


Mainframe VSAM

INDEXED), SDS NONINDEXED), OR RRDS NUMBERED). The default is INDEXED.

RECORDSIZE ( avg max) Specifies the average and maximum record size.

CISZ (Size) Specifies the size of the control intervals.

SPANNED / NONSPANNED Specifies whether records can cross control interval boundaries. The default is NONSPANNED.

KEYS (length offset) Specifies the length and offset of the primary key.

FREESPACE (ci ca) specifies the percentage of free space to reserve in the control intervals and control areas.

VOLUMES (Vol-ser) Specifies one or more volumes that will contain the cluster or component.

FILE (dd name) Specifies a dd name that identifies a DD statement that allocates the

volumes .Required only for mountable DASD volumes.

Primary Specifies the amount of space to initially allocate, expressed in terms of cylinders, kilobytes, megabytes, tracks or records.

Secondary Specifies the secondary space allocation.

UNIQUE/SUBALLOCATION Specifies whether the file is unique or sub allocated. The default is

SUBALLOCATION.

REUSE / NOREUSE Specifies whether a file is reusable. The default is NOREUSE.

SHAREOPTIONS ( a b) Specifies the level of the file sharing permitted.

IMBED / NOIMBED Specifies whether sequence set records should be imbedded in the data component of a KSDS. The default is NOIMBED.

CATLOG (name[/password]) Specifies the name and password of the catalog that will own the cluster. If omitted, the high- level qualifier of the cluster name or the stepcat, jobcat, or master catalog identifies the catalog.

NAME is a positional keyword parameter and must be coded first. Other

keywords can be placed anywhere

EXAMPLES OF THE DEFINE CLUSTER:

Example #1

Define a key-sequenced data set (KSDS)

DEFINE CLUSTER ( NAME (MTRG.CUSTOMER.MASTER) -

OWNER(MTRG) -

INDEXED -


Mainframe VSAM

RECORDSIZE(80 80) -

KEYS(6 0) -

VOLUMES(SMS007) -

UNIQUE -

SHAREOPTIONS( 2 3) -

IMBED) -

DATA ( NAME(MTRG.CUSTOMER.MASTER.DATA) -

CYLINDERS(50 5) -

CISZ(4096) ) -

INDEX ( NAME(MTRG.CUSTOMER.MASTER.INDEX))

Example #2

Define an entry-sequenced data set (ESDS)

DEFINE CLUSTER (NAME (MTRG.CUSTOMER.MASTER) -

OWNER (MTRG) -

NONINDEXED -

RECORDSIZE (180 80) -

VOLUMES (SMS007) - REUSE)

-

DATA ( NAME (MTRG.CUSTOMER.MASTER.DATA) -

CYLINDERS (50 5) )

Example #3

Define an relative-record data set (RRDS)

DEFINE CLUSTER (NAME (MTRG.CUSTOMER.MASTER) -

OWNER (MTRG) -

NUMBERED -

RECORDSIZE (180 80) -

VOLUMES (SMS007) - UNIQUE)

-

DATA (NAME (MTRG.CUSTOMER.MASTER.DATA) -

CYLINDERS (50 5) )

REVIEW QUESTIONS:

1. What is IDCAMS? And what is the purpose of it?

2. What is the significance of the SHAREOPTIONS parameter?

3. What is the use of REPRO command?

4. What are the different types of AMS commands?

5. What are the basic IDCAMS commands?

6. AMS will generate a data component name if it is not explicitly coded.


Mainframe VSAM

a) TRUE

b) FALSE

7. What are the parameters used in AMS commands?

8. Can AMS commands be run from the TSO prompt?

9. What is the base cluster?

CHAPTER - 5: Creation of Clusters

CREATION OF VSAM DATA SETS THROUGH JCL

A Data Class is a description of data set characteristics under control of SMS.

JCL parameter overrides the specifications from a Data Class. VSAM accomplishes JCL simplification by centralizing functions such as defining, deleting, and altering file characteristics in the AMS Utility program. VSAM has much simpler JCL requirements than files of other access methods.

How to allocate existing VSAM files

The DSNAME parameter

The DUMMY parameter

The DISP parameter

The AMP Parameter

How to create VSAM files using JCL.

The DD statement for allocating existing VSAM File

//ddname dd DSNAME={data-set-name}

{Dummy}[,Disp={old/shr},Normal-disp,Abnormal-disp]

[,AMP=(option,option….)]

Explanation:


// DD statement………… with new parameters and/orinfo from ‘DATA CLASS’

Mainframe VSAM

DSNAME Specifies the name of the VSAM dataset. Normally, the high level qualifier of the name identifies the owning catalog.

DUMMY Specifies that a VSAM file should not be allocated; instead, MVS should simulate a VSAM FILE.

DISP Specifies the file’s status and, the file’s normal & abnormal disposition. The valid status options are OLD for exclusive access and SHR for shared access. All of the disposition options except UNCATLG are valid for VSAM files.

AMP Specifies one or more processing options for VSAM files.

The AMP parameter

The AMP parameter is for VSAM files & the DCB parameter is for non-VSAM files. It specifies execution time information that affects how the file is processed.

The AMORG sub parameter

AMORG indicates that the files being accessed is a VSAM file. Normally, MVS realizes that a VSAM file is being processed when it retrieves the catalog information for the file. So we need to specify AMP=AMORG when MVS doesn’t search the catalog.

The AMP parameter

AMP=[ AMPORG]

[,BUFND=n]

[,BUFNI=n]

[,BUFSP=n]

[,OPTCD=OPTIONS]

[,RECFM=FORMAT]

[,STRNO=N]

Explanation

AMORG Specifies that the data set is a VSAM file. Normally not required.

BUFND Specifies the number of buffers to allocate for the data component.

BUFNI Specifies the number of buffers to allocate for the index component.

BUFSP Specifies the total amount of space in bytes to allocate for the data and index buffers.

OPTCD options for the ISAM interface. Code I , L, or IL. ‘I ‘ means that if OPTCD=L is specified for the file in the processing

program, records marked for deletion by hex FF in the first byte should be physically deleted from the file. If OPTCD=L is not specified in the program, Specify OPTCD=IL in the DD statement for the same effect.

RECFM Specifies the format in which the ISAM program expects to process records.

STRNO Specifies the number of concurrent requests the program may issue against the file.


Mainframe VSAM

Example #1

//CUSTMAST DD DSNAME=MTRG.CUSTOMER.MASTER, DISP=SHR,

// AMP=(BUFND=2,BUFNI=6)

Allocate a VSAM file for shared access, specifying that 2 data buffers

and 6 index buffers should be used.

Example # 2

//CUSTISAM DD DSNAME=MTRG.CUSTOMER.MASTER,DISP=SHR,

// AMP=(AMORG,OPTCD=IL,RECFM=FB)

Allocate VSAM file using the ISAM interface program, AMORG identifies

the file as VSAM, OPTCD specifies how logically deleted records should be handled and RECFM specifies that the program expects fixed-length blocked records.

NEW PARAMETER USED IN VSAM

RECORG =

KEYOFF = offset-to-key

(for KSDS Only)

KEYLEN =Bytes

(for KSDS and some non-VSAM data sets)

RECORG parameter

o KS specifies a VSAM key-sequenced data set

o ES specifies a VSAM entry-sequenced data set

o RR specifies a VSAM relative record data set.

o LS specify a VSAM linear space data set.

o

o KSDS (EX1)

o

o

o

o

o

o

o

o


ESKSRRLS

KSDS //DD1 DD DSNAME = MY.KSDATA, // DISP=(NEW,CATLG), // SPACE=(400,(50,5)), // AVGREC=K, // RECORG =KS // KEYLEN= 15, // KEYOFF=0, // LRECL=250

Mainframe VSAM

o ESDS (EX2)

o

o

o

o

o

o

o RRDS (EX3)

o

o

o

o

o

o

o Not all VSAM options can be specified in the JCL, more options and defaults may come from a Data class.

EX1 shows a JCL statement containing all required information for a KSDS data set.

Ex2 shows a JCL statement containing all required information for an ESDS data set.

Ex 3 shows a JCL statement of a temporary linear data set. This example requires the assignment of a so-called storage Class.

REPRO Command

REPRO is an all-purpose load and backup utility command .

It loads an empty VSAM cluster with records. The data and index components (for a KSDS) are build automatically.

It creates a backup of a VSAM dataset on a physical sequential dataset, and then restore and rebuilds the VSAM dataset using this dataset as input

It merges data from two VSAM datasets.

REPRO terminates if One physical I/O error while writing to the output

dataset.

A total of four errors encountered in any combination:

A logical error while writing to the output data set.

A logical error while reading the input data set.

A physical error while reading the input data set.

CREATION OF ESDS CLUSTER

The definition of an ESDS cluster with the parameters described above.

//IFMAIN2 JOB (12345678),IFMAIN2,MSGCLASS=H,

// MSGLEVEL=(1,1),CLASS=A,NOTIFY=&SYSUID


// DD2 DD DSNAME=MY.ESDATA // DISP=(NEW,CATLG), // SPACE=(100,(10,8)), // RECORG =ES // LRECL=50

LINEAR //DD3 DD DSNAME=&LIN, // DISP=(NEW,PASS), // SPACE=(1,(10)), // AVGREC=M, // RECORG=LS

Mainframe VSAM

//STEP1 EXEC PGM=IDCAMS

//SYSOUT DD SYSOUT=*

//SYSPRINT DD SYSOUT=*

//SYSIN DD *

DEFINE CLUSTER -

(NAME (IFMAIN2.esds.CLUST) -

RECORDSIZE (80,80) -

TRACKS(5, 1) -

CISZ(4096) -

NONINDEXED -

REUSE) -

DATA (NAME(IFMAIN2.IFRAME.CLUST.DATA))

/*

//

The above example shows the creation of an ESDS cluster. After the execution of this JCL the blank cluster will be created and it will be in the user catalog for usability.

COPYING ENTIRE DATA SETS

The following screen shot will copy the EMP1.PS content to the above created ESDS cluster, KSDS

In this example, an entire input data set is copied to the output data set.

Two parameters of REPRO are used.

INDATASET (or IDS) Name of the entry to be copied or of the user catalog to be merged.

OUTDATASET (or ODS) Name of the target data set.

Both INDATASET and OUTDATASET can be used to reference VSAM or non-VSAM data sets.

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID




//DD1 DD DSN=IFMAIN2.EMP1.PS,DISP=SHR

//DD2 DD DSN=IFMAIN2.ESDS.CLUSTER,DISP=SHR

//SYSIN DD *

REPRO INDATASET(IFMAIN2.EMP1.PS) -

OUTDATASET(IFMAIN2.ESDS.CLUSTER)

/*

//

CREATION OF KSDS CLUSTER WITH REUSE OPTION.


Mainframe VSAM

REUSE specifies that the cluster can be loaded with fresh records with an implicit delete of existing records. The REUSE parameter can be specified on both the DEFINE CLUSTER and the REPRO command.

Example:

//ifmain2 job notify=&sysuid //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * DEFINE CLUSTER(NAME(IFMAIN2.KSDS.CLUSTER)- TRACKS(2,5)- RECORDSIZE(80,80)- CONTROLINTERVALSIZE(512)- FREESPACE(20,20)- KEYS(4,0)- REUSE- INDEXED))- DATA(NAME(IFMAIN2.KSDS.DATA))- INDEXED(NAME(IFMAIN2.KSDS.INDEX)) /* // REUSE cannot be used under following circumstances and hence not

recommended

When KEYRANGES parameter is coded

When alternate indexed are defined

CREATION OF RRDS CLUSTER

The following screenshot shows the definition of an KSDS cluster with the parameters described above

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * DEFINE CLUSTER(NAME(IFMAIN2.RRDS.CLUSTER)- TRACKS(2,5)- RECORDSIZE(80,80)- CONTROLINTERVALSIZE(512)- NUMBERED))- DATA(NAME(IFMAIN2.RRDS.DATA)) /* // REPRO RECORD SELECTION

DATA set can be copied partially using starting and ending delimiter parameters on the REPRO command


Here the KSDS cluster is created with REUSE option

Mainframe VSAM

number = Number of records

key-value = Record key for a KSDS

rba = relative byte address for a record in a KSDS or ESDS

rrn = Relative record number(slot) for RRDS records

Where to start Where to stop

KSDS FROMKEY (rec-key) TOKEY (rec-key)

KSDS, ESDS FROMADDRESS(rba) TOADDRESS(rba)

RRDS FROMNUMBER (rrn) TONUMBER (rrn)

KSDS, ESDS SKIP(number) COUNT(number)

RRDS, ISAM

The Following The Selection Of Records In Different VSAM Files.

ESDS CLUSTER





//INPUT DD DSN=IFMAIN2.ESDS.CLUSTER,DISP=SHR

//SYSIN DD *

PRINT-

INFILE(INPUT)-

CHAR-

FROMADDRESS(0)TOADDRESS(160)

/*

//

The above program will display only the selected RBA address records which

are shown by the following screenshots.

KSDS CLUSTER

The following use the keys to select the particular records from the kSDS cluster

Example:






Mainframe VSAM

//INPUT DD DSN=IFMAIN2.KSDS.CLUSTER,DISP=SHR

//SYSIN DD *

PRINT-

INFILE(INPUT)-

CHAR-

FROMKEY(1000)TOKEY(1004)

/*

//

RRDS CLUSTER

The following screen shots use the keys to select the particular records from the kSDS cluster





//INPUT DD DSN=IFMAIN2.RRDS.CLUSTER,DISP=SHR

//SYSIN DD *

PRINT-

INFILE(INPUT)-

CHAR-

FROMNUMBERED(1000)TONUMBERED(1004)

/*

//

REVIEW QUESTIONS:

1. Which of the following repro selection parameters can be specified for an

LDS?

a) From key b) from address

c) From number d) skip e) none of the above.

2. REPRO will stop processing records when a total of four physical I/O errors

occur while writing to the output data set.

A. TRUE

B. FALSE

C.

D. 3. REPRO REUSE against a non-empty target data set with NOREUSE will reset target data set.

A. TRUE

B. FALSE

C.


Mainframe VSAM

D. 4. AMS will generate a data component name if it is not explicitly coded.

A. TRUE

B. FALSE

C.

D. 5. When defining a KSDS, which of the following parameters is not required?

E.

A. Space allocation (either CYL, REC or TRK)

B. VOLUMES

C. KEYS

D. NAME

E.

F. 6. DEFINE CLUSTER for a KSDS will generate CLUSTER, DATA and INDEX information even if only CLUSTER information is specified.

A. TRUE

B. FALSE

C.

D. 7. A “candidate” volume is not used when the data set is initially loaded.

A. TRUE

B. FALSE

C.

D. 8. If the key of a KSDS record begins in the second field (first field is 25 bytes long), the offset in the KEYS parameter is:

E.

F. a) 24 b) 25 c) 26 d) None of the above.

G.

H. 9. Suppose TEST.DATASET is a KSDS. The following statement will print CLUSTER information only: LISTCAT ENTRIES (TEST.DATASET) ALL

a. TRUE

b. FALSE.

c.

d.

e.

f.

g.

h.

i.

j.

k.

l.

m.

n.

o.

p.


Mainframe VSAM

q.

r. CHAPTER --- 6 : Print and Additional Commands

s.

t. PRINT COMMAND

u. The PRINT command of Access Method Services is used to print the contents of both VSAM and non-VSAM data sets. The command syntax is similar to that of REPRO. While REPRO copies an input data set into another output data set, PRINT dumps an input data set to a printer. This command is versatile and can be used to print a complete data set or only a selected part of it.

v.

w. The PRINT command

x.

y. PRINT { INDATASET(entry-name [/ password])}

z. [{CHARACTER/HEX/DUMP}]

aa. [{SKIP(count)/

FROMKEY(key)/FROMNUMBER(number)/FROMADDRESS(address)}]

bb.[{COUNT(count)/TOKEY(key)/TONUMBER(number)/TOADDRESS(address)]

cc.

dd. Explanation

ee. CHARACTER/HEX/DUMP -Specifies the format of the output. CHARACTER & HEX print the data in character or hex format. DUMP prints data in both character and hex format. DUMP is default.

ff.

gg. Example

hh. To print records 29, 30 & 31 in character format.

ii. PRINT INDATASET(MTRG.CUSTOMER.MASTER) -

jj. CHARACTER -

kk. SKIP(28) -

ll. COUNT(3)

mm.

nn. To print records 29,30 & 31 in dump format.

oo. PRINT INDATASET (MTRG.CUSTOMER.MASTER) -

pp. DUMP -

qq. SKIP(28) -

rr. COUNT(3)

ss.

tt. Example:

uu. //ifmain2 job notify=&sysuid

vv. //step1 exec pgm=idcams

ww. //sysprint dd sysout=*


Mainframe VSAM

xx. //sysout dd sysout=*

yy. //input dd dsn=ifmain2.rrds.cluster,disp=shr

zz. //sysin dd *

aaa. Print-

bbb. Infile(input)-

ccc. Char-

ddd. Skip(1)-

eee. Count(3)

fff. /*

ggg. //

hhh.

iii. EXPORT/IMPORT COMMAND

jjj. Export extracts catalog information and creates a copy of the data records. When a base cluster and its alternate index are permanently exported, the alternate index must be exported before the base cluster. When exporting a data set for backup purpose specify TEMPORARY to preserve the original data set.

kkk.

lll. EXPORT IMPORT

mmm.

nnn. Advantages

Used for backup and recovery

Catalog information also exported along with the data, unlike REPRO

DFSMS classes are preserved

Cluster deletion and redefinition are not necessary during the import

Can be easily ported to other systems

Disadvantages

The EXPORTED file not reusable until it is imported

Slower than REPRO


Mainframe VSAM

SYNTAX FOR EXPORT

EXPORT entryname[/password] -

{outfile(ddname) outdataset(entryname)} -

[CIMODE | RECORDMODE] -

[TEMPORARY | PERMANENT] -

[INHIBITSOURCE

NOINHIBITSOURCE] -

[INHIBITTARGET

|NOINHIBITTARGET] -

[ERASE | NOERASE] -

[PURGE | NOPURGE]

RECORD MODE – RECORDS ARE EXPORTED ONE LOGICAL RECORD AT A TIME.

RECORDMODE is the default for ESDS, KSDS, and RRDS.

CIMODE – CI rather than logical record exports data. CIMOD is default for LDS.

TEMPORARY – The data set is not deleted after export.

PERMANENT- The data set is deleted after export.

INHIBITSOURCE – The original data set becomes read-only.

NOINHIBITSOURCE - The original data can be updated.

INHIBITTARGET - The copy data set becomes read-only.

NOINHIBITTARGET - The target data set can be updated.

ERASE - Causes the exported item to be overwritten with zeros when it is deleted.


Catalog Data set

EXPORT

Mainframe VSAM

NOERASE – Override whatever was specified for the item when it was created.

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //DD1 DD DSN=IFMAIN2.BACKUP.PS, // DISP=(NEW,CATLG,DELETE), // UNIT=SYSDA, // SPACE=(TRK,(2,3),RLSE), // DCB=(LRECL=80,RECFM=FB,BLKSIZE=800,DSORG=PS) //SYSIN DD * EXPORT- IFMAIN2.KSDS.CLUSTER- OUTFILE(DD1) /* // Now the above exported file is not available in user catalog. It is

permanently exported to the new PS which is created. To get back the exported cluster we want to use import option to get back it in our user catalog. This is illustrated in the following snapshots.

SYNTAX OF IMPORT

IMPORT-

{INFILE(DDNAME) | INDATASET(ENTERYNAME)} –

{OUTFILE(DDNAME) | UTDATASET(ENTERYNAME)} -

[OBJECTS((ENTERYNAME - [NEWNAME(NAME)] -

VOLUMES(VOLSER])[ENTRYNAME….)])] –

[INTOEMPTY]

NEWNAME – Objects beginning imported can be renamed.

VOLUMES – Specifies the volume on which the cluster is to reside if omitted the original volume is the receiving volume

INTOEMPTY – Indicates that the receiving dataset is empty.

On IMPORT the existing catalog entry is deleted unless the receiving data set

is empty.


Mainframe VSAM

The following procedure provides backup and recovery capabilities and also

permits the modification of data set attributes when the data set is imported during recovery or reorganization.


Catalog Data set

IMPORT

STEP 1EXPORT

STEP 4IMPORTINTOEMPTY

ORIGINALMASTER

STEP 2DELETE

STEP 3DEFINE NEW

MASTER

Mainframe VSAM

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //DD1 DD DSN=IFMAIN2.BACKUP.PS, //SYSIN DD * IMPORT- INFLIE(DD)- OUTDATASET(IFMAIN2.KSDS.CLUSTER) /* // VERIFY COMMAND

Verifies the catalog HURBA (High Used Relative Byte Address) field and stores the true values from the control block HURBA field.

It should be used against cluster name only and not against data or index components.

It is used to rectify some of the problems due to data corruption

It can be issued from TSO or from a JCL

Syntax: VERIFY FILE (<dd name>)

VERIFY DATASET (<dataset name>)

Compares Catalog Information with the Data Set

Corrects Catalog If A Disagreement Is Found

Run VERIFY after a system failure.

When sharing data sets, run VERIFY before opening a data set.

VERIFY cannot be used for an empty data set or an LDS.


TEST.DATA.SET

END-OF-DATA

END-OF-KEY-RANGE

END-OF-DATA

END-OF-KEY-RANGE

?

Mainframe VSAM

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * VERIFY DATASET(IFMAIN2.KSDS.CLUSTER) /* // LISTCAT

LISTCAT Command identify the catalog, the names of the entries to be listed, the types of entries to be listed, and the amount of information about each entry to be listed.

LISTCAT [ CATALOG (name) ]

[ ENTRIES (name - of - entries) ]

[LEVEL (generic-level-names)]

[ NAME/HISTORY/VOLUME/ALLOCATION/ALL}]

Catalog(name[/password]) Specifies the name and if, required,

password of the catalog from which entries are to be listed.

ENTRIES(entry-name[/password]) Specifies the names of the entries you want to list. If omitted, all entries in the specified catalog are listed.

LEVEL(level) Specifies one or more levels of qualifications. Any data sets whose name matches those levels are listed.

Entry –type Specifies the type of entries you want listed. If both ENTRIES / LEVEL and entry-type are omitted, all entries of all types in the

specified catalog are listed. Code one of these values: ALIAS, CLUSTER, DATA, INDEX, & PATH

NAME Specifies that only the names and types of the specified entries are to be listed. Name is the default.

HISTORY Specifies that the information listed by NAME, Plus the history information (such as creation and expiration dates) is to be listed.

VOLUME Specifies that the information listed by HISTORY, plus the volume locations of the specified entries, is to be listed.

ALLOCATION Specifies that the information listed by VOLUME, plus detailed extent information, is to be listed.


Mainframe VSAM

ALL Specifies that all available catalog information for the specified entries is to be listed.

Examples

To list the catalog entry for a VSAM file named MTRG.CUSTOMER.MASTER

ENTRIES (MTRG.CUSTOMER.MASTER)

To list information for more than one file, just code several file names in a single ENTRIES parameter, like this:

ENTRIES (MTRG.CUSTOMER.MASTER -

MTRG.SUPPLIER.MASTER -

MTRG.ITEM.TRANS)

We can specify a generic entry name by replacing one or more levels of the file name with an asterisk.

ENTRIES (MTRG.*.MASTER)

All files whose names consists of three levels with MTRG as the first level and MASTER as the third level, are listed. MTRG.CUSTOMER.MASTER AND MTRG.SUPPLIER.MASTER meet these criteria, so they would be listed.

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * LISTCAT ENTRIES(IFMAIN2.VSAM.PDS) LISTCAT ENTRIES(IFMAIN2.VSAM.*) /* // ALTER

We can use this powerful command to change certain attributes of previously defined VSAM object. These objects include base cluster and it’s data and index component and even alternate index cluster and it’s data or index component and even a VSAM or ICF catalog. If you are properly authorized you can ALTER NON-VSAM data set attributes also.


Mainframe VSAM

SYNTAX OF ALTER COMMAND

ALTER entryname[/password] -

SHAREOPTION(cross region cross system)

Examples:

ALTER MTRG.CUSTOMER.MASTER -

NEWNAME(MTRG.CUSTMAST)

ALTER EMPLOYEE.KSDS.CLUSTER

FREESPACE(25,25)

Change the filename of MTRG.CUSTOMER.MASTER to MTRG.CUSTMAST

ALTER MTRG.CUSTOMER.MASTER.DATA -

ADDVOLUMES(VOL291 VOL292) -

REMOVEVOLUMES(VOL 281 VOL 282)

Add VOL291 and VOL292 to list of eligible volumes for

MTRG.CUSTOMER.MASTER.DATA and remove VOL281 and VOL282.

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * ALTER IFMAIN2.KSDS.DATA – NEWNAME(IFMAIN2.VSAM.KSDS) /* // Likewise we can alter the other data attributes like:

ADDVOLUME

ATTEMPTS


ALTER EXAMPLE.KSDSSHAREOPTIONS(2 3)

CATALOG CATALOG

EXAMPLE.KSDS SHAREOPTIONS(1 3)

EXAMPLE.KSDS SHAREOPTIONS(2 3)

Mainframe VSAM

SHAREOPTIONS

BUFFERSPACE

FREESPACE

PASSWORD

ENTRY NAME is the cluster, data or index component name.

PASSWORD is the master password if the VSAM data set is password protected

ALTER can also be used as a migration path to change an ESDS to LDS

ALTER with ADDVOLUME/REMOVEVOLUME

ADD VOLUME:

//ALTJOB JOB ,,NOTIFY=userid



//SYSIN DD *

ALTER -

USER1.KSDS.DATA -

ADDVOLUMES(VS012)

REMOVE VOLUME:

ALTER

USER1.KSDS.DATA -

REMOVEVOLUME(RTD2)

ALTER WITH FREESPACE


FREESPACE(CI-percent[ CA-percent]))

Example:

//ALTJOB JOB ……….



//SYSIN DD *

ALTER -

USER1.KSDS.DATA -

FREESPACE(30 30)

Entryname must be the name of the cluster’s data component.

This procedure has the following advantages.


Mainframe VSAM

It prevents wasting space.

It minimizes CI and CA splits.

ALTERING PASSWORD

Adding/Changing PASSWORD


[READPW (password)] -

[UPDATEPW (password)] -

[CONTROLPW (password)]-

[MASTERPW (password)]

Nullifying PASSWORD


NULLIFY -

[READPW] -

[UPDATEPW] -

[CONTROLPW] -

[MASTERPW ]

DELETE COMMAND

DELETE command is used to remove entries from a VSAM catalog. To delete more than one file, list the names in parentheses. The IDCAMS DELETE command can be used to delete both VSAM and non-VSAM objects

SYNTAX:

DELETE entry name/password

Example 1

We can specify a generic name in a DELETE command by replacing ONE level of the entry name with an asterisk, like this

DELETE MTRG.CUSTOMER.*

Example 2

To delete MTRG.CUSTOMER.MASTER, whether or not it is expired.

DELETE MTRG.CUSTOMER.MASTER –

PURGE

Example 3

To delete the 3 named files.

DELETE ( MTRG.CUSTOMER.MASTER -

MTRG.CUSTMAST.AIX -

MTRG.CUSTMAST.PATH)

Example:

//IFMAIN2 JOB NOTIFY=&SYSUID //STEP1 EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * DELETE IFMAIN2.KSDS.CLUSTER


Mainframe VSAM

/* // Some other options for Delete are:

ALIAS

ALTERNATEIND

CLUSTER

SPACE

PURGE

PATH

REVIEW QUESTIONS:

1. The default print format is:

a. character

b. dump

c. hexadecimal

d. none of the above.

e. 2. Which of the following repro selection parameters can be specified for an LDS?

A. from key

B. from address

C. from number

D. skip

E. none of the above

F. 3. The replace parameter causes:

a. KSDS records to be replaced by an input record with the same key

b. ESDS records to be replaced by an input record with the same RBA

c. RRDS records to be replaced by an input record with the same RRN

d. a) and c)

e. all of the above

f. 4. Generic keys can be specified in PRINT FROM KEY and TOKEY

A. TRUE

B. FALSE

C. 5. REPRO will stop processing records when a total of four physical I/O errors occur while writing to the output data set.

A. TRUE

B. FALSE

C. 6. Which of the following is not a valid command?

a. IF

b. THEN

c. ELSE

d. DO

e. GOTO


Mainframe VSAM

f. 7. REPRO REUSE against a non-empty target data set with NOREUSE will reset the target data set.

A. TRUE

B. FALSE

C. 8. Can VSAM files be deleted with the DELETE option of the DISPOSITION parameter of JCL?

D. 9. During processing of a VSAM file, some system error occurs and it is subsequently unusable What do you do?

E.

F.

G. CHAPTER --- 7 : Alternate Indexes

H. An alternate index is used to an access the records of a VSAM key-sequenced data set in an order other than the file’s primary key (or base key). The data set over which an alternate index exists is called a base cluster. Even we can use an entry-sequenced data set as the base cluster for an alternate index, most alternate indexes are built over KSDS clusters. Used whenever the data is required to be retrieved on the basis of other field (than primary key field). An alternate index cannot be defined for RRDS or LDS

I.

J.


ALTERNATE INDEX 1(DEPT NO)

ALTERNATE INDEX 2(SOCIAL SEC NO)

3235 NEWTON $…3240 WRIGHT $..3247 ADAMS $..3247 PETTY $ …

ADAMS 3247 $…ARNOLD 4711 $…KINNEY 3247 $……NEWTON 3235 $..

015-35-7890 WRIGHT $..183-96-416 ADAMS $…234-04-2372 PETTY $..

BASE CLUSTER(NAME)

Mainframe VSAM

K. MULTIPLE ALTERNATE INDEXES (AIXs) may be defined over a base cluster.

L. If the user is sequentially retrieving records using AIX1, then department number retrieves records in logical sequence Access via AIX2 with an alternate key of social security number results in the retrieval of base cluster records in social security number sequence.

M. ADVANTAGES

Can be defined for both KSDS & ESDS

Reduce data redundancy

Can have duplicates

Easy to define using IDCAMS

Allow datasets to be accessed sequentially or randomly

Can be updated automatically

DISADVANTAGES

Performance degradation

Complex update logic

NEED FOR ALTERNATE INDEX:

Alternate Indexes save sorting or maintaining duplicate data that might otherwise be required.An alternate index cannot be defined for an RRDS or LDS

KSDS

A. ACCESS A KSDS BY KEY OTHER THAN THE PRIMARY KEY

1. SOCIAL SECURITY NUMBER

2. DEPARTMENT NUMBER

3. EMPLOYEE NUMBER

4. ZIP CODE

5. B. ACCESS AN ESDS BY KEY


INDEX: EMPLOYEE NAME

DATA: EMPLOYEE RECORDS

Mainframe VSAM

6.

7. ALTERNATE INDEX DATA RECORD FORMAT

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18. Each AIX data record is variable length and contains system header information, the alternate key and at least one pointer to the base cluster. AIX s are spanned record data sets, since there may be many base cluster records associated with a given alternate key.

19. Pointers to the base cluster are of two forms, either an RBA (for an ESDS base cluster)or a prime key for a ksds base cluster).The pointers are the same type throughout the entire AIX.

20.

21.ALTERNATE INDEX ORGANIZATION

Alternate Indexes are KSDS by themselves and have their own data and index components

AIX data components contain the alternate index key values and pointers to each record containing the key value

AIX index components contain highest key value in an AIX data CI and a pointer to that CI

AIX data component has variable length records if duplicate is allowed (due to multiple pointers)

STEPS FOR CREATING ALTERNATE INDEX

Define AIX using IDCAMS DEFINE AIX

Build AIX & populate it using IDCAMS BLDINDEX

Specify Alternate Index Path using IDCAMS DEFINE PATH

CREATING AN ALTERNATE INDEX

DEFINE ALTERNATEINDEX-

(NAME(AIX NAME)-

RELATE(BASE CLUSTER NAME)-

KEYS (LENGTH OFFSET)-

UNIQUEKEY/NONUNIQUEKEY-

UPGRADE/ NOUPGRADE

RECORDSIZE (AVG MAX)-

VOL (VOLSER) –


PRIME KEY LENGTH * NUMBER NONUNIQUE PRIME KEYS RECORD = 5 + ALTERNATE KEY + -0R- SIZE LENGTH 4 *NUMBER NONUNIQUE POINTERS POINTERS

Mainframe VSAM

CYL/TRK/REC(PRI SEC))

NAME

Syntax: NAME

Required parameter: Specifies the name of AIX

VOLUMES

Syntax: Volumes (Vol-ser-1 ..... vol-ser-n)

Required parameter: Assigning base cluster & AIX in different volumes improves performance

RELATE

Syntax: RELATE (base cluster name)

Required parameter: Establishes relationship between the base cluster & AIX

UPGRADE/NOUPGRADE

Syntax: UPGRADE/NOUPGRADE

UPGRADE specifies that records in AIX are to be updated automatically whenever the base cluster is updated .The use of UPGRADE makes the alternate index part of the cluster’s so called “UPGRADE SET”

Default: UPGRADE

AIX 1

AIX 2 AIX 3

Base cluster

KEYS

Syntax: KEYS (length offset)

Optional: primary key values are taken as default, if not specified.Defeats the purpose of Alternate Index, if not specified

RECORD SIZE


Mainframe VSAM

Syntax: RECORD SIZE (average maximum)

Default: RECORDSIZE (4086 32600)

Abbr: RECSZ

Average & max. Are same for UNIQUEKEY AIX and may be different for NONUNIQUEKEY

HOW TO CALCULATE THE RECORD SIZE?

AIX for a KSDS RECSZ = 5 + AIXKL + (n x BCKL)

AIX for ESDS RECSZ = 5 + AIXKL + (n x 4)

Where:

AIXKL is the alternate-key length

BCKL is the base cluster's prime-key length

n = 1 when UNIQUEKEY is specified

n = the number of data records in the base cluster that contain the same alternate-key value, when NONUNIQUEKEY is specified.

Other AIX parameter

ATTEMPTS

AUTH (entry point)

BUFFERSPACE (bytes)

CATALOG (catalog/pw)

CODE (code)

CISZ (bytes)

CONTROLPW (password)

ERASE (NOERASE)

EXCEPTIONEXIT (entry point)

KEYRANGES (low-key high key)

MASTERPW (password)

ORDERED/UNORDERED

READPW (password)

REPLICATE/NOREPLICATE

REUSE/NOREUSE

SHAREP[TOPMS

SPEED/RECOVERY

UNIQUEKEY/NONUNIQUEKEY

UPDATEPW (password)

WRITECHECK/NOWRITECHECK

EXAMPLE:

//STEP1 EXEC PGM =IDCAMS


Mainframe VSAM


//SYSIN DD *

DEFINE ALTERNATEINDEX(USER1.KSDS.AIX)-

VOLUME(V001) -

RELATE(USER1.KSDS.CLUSTER)-

UPGRADE-

CYLINDERS(2 1)-

KEYS(25 9)-

RECORDSIZE(70 110)-

FREESPACE(20 10)-

NONUNIQUEKEY-

DATA

(NAME(USER1.KSDS.AIX.DATA))-

INDEX

(NAME(USER1.KSDS.AIX.INDEX))

BUILD INDEX

SYNTAX:

BLDINDEX

{INFILE(ddname) / INDATASET (base cluster name)} -

{OUTFILE(ddname) / OUTDATASET (AIX NAME)} -

[EXTERNALSORT / INTERNALSORT] -

[WORKFILES(ddname ddname) ]

INFILE /INDATASET IDENTIFIES THE BASE CLUSTER.

OUTFILE / OUTDATASET IDENTIFIES THE AIX TO BE LOADED

INTERNALSORT Requires AMS to build the Alternate Index Records

within the user’s address space if possible

EXTERNALSORT Indicates that two ESDS work Files are to be used by AMS for the sort

WORKFILES Specifies The DD names to be used instead of the default Names

EXAMPLE

BLDINDEX INDATASET(USER1.KSDS.CLUSTER)-

OUTDATASET(USER1.KSDS.AIX)

CREATION OF PATH

Once you have defined any alternate indexes, You must define a separate path for each one, using the IDCAMS DEFINE PATH command.

This path name is the dataset name that you use in the jcl when processing an alternate index. It is a separate catalog entry and forms a logical connection(path) through the alternate index to the base cluster

A path is a catalog record. It is normally used to relate the alternate index and the base cluster


Mainframe VSAM

IDCAMS DEFINE PATH is used to create a path record in the catalog.

SYNTAX:

DEFINE PATH(NAME(PATH NAME) -

PATHENTRY(AIX NAME) -

UPDATE / NOUPDATE)

NAME specifies the name of the PATH.

PATHENTRY associates the AIX with the path name.

UPDATE / NOUPDATE specifies whether all of the upgrade set should be maintained by VSAM when accessing through this path

EXAMPLE:

DEFINE PATH ( -

NAME(USER1.KSDS.PATH) –

PATHENTRY(USER1.KSDS.AIX)-

UPDATE )

ALTERNATE INDEX FOR ESDS

Same syntax & parameters as KSDS

Not supported in Batch COBOL (OS/VS & VSII)

Used under CICS environment

Step 2: BUILDING THE INDEX

BLDINDEX Command actually builds the index and populates it with records

//BLDINDX EXEC PGM=IDCAMS


//DD1 DD DSN=XIND.NLT.VSAM,DISP=OLD

//DD2 DD DSN=XIND.NLT.VSAM.DEPT.AIX,DISP=OLD

//IDCVT1 DD DSN=XIND.NLT.WRKFILE1, DISP=OLD

//IDCVT2 DD DSN=XIND.NLT.WRKFILE2, DISP=OLD

//SYSIN DD *

BLDINDEX INFILE (DD1) OUTFILE (DD2) -

INTERNALSORT

/*

Step 3: SPECIFYING THE ALTERNATE INDEX PATH

Example:

DEFINE PATH -

(NAME(XIND.NLT.VSAM.DEPT.PATH) -

PATHENTRY -

(XIND.NLT.VSAM.DEPT.AIX) UPDATE)

- Path is a VSAM object though it doesn’t contain any records

- Same command for KSDS & ESDS


Mainframe VSAM

- Path is used to link JCL DSN to VSAM AIX (specifies that the given AIX is to be used).

NAME

Syntax: NAME (pathname). Pathname becomes the DSN in the run JCL

PATHENTRY

Syntax: PATHENTRY (entry name/password).

Entry name: name assigned to alternate index cluster. Required for an alternate index

RESTRICTIONS FOR ALTERNATE INDEX

No Alternate Index For RRDS and LDS.

Base Cluster Must Not Be Empty For Buildindex.

Length Of The Alternate Index Not Exceed 255

Maximum Number Of Alternate Key Pointers Is 32k.

Records Larger Than 32760 Not Supported By Repro/Export.

For A Base Cluster With Alternate Index(Es) And Path(S),Delete Cluster

Deletes Not Only The Base Cluster But Also The Associated Alternate Index

Maximum Alternate Indexes Can Be 253 For A Single Dataset(ESDS&KSDS)

REVIEW QUESTIONS:

1. An alternate index can be defined for which cluster type(s)?

a.) KSDS AND RRDS

b) KSDS AND ESDS

c) KSDS only

d) KSDS,ESDS AND RRDS.


Mainframe VSAM

2. The size of an alternate index is about the same of it’s base cluster.

a) true

b)false

3. If an application program accesses a base cluster in alternate key sequence,

then DD statements are needed for which data set(s)?

a) Base cluster

b) alternate index

c) path

d) (a) and(b)

e) (a) and c

4. An alternate index itself is which cluster type?

a) LDS

b) RRDS

c) ESDS

d) KSDS

e) NONE OF THE ABOVE.

5 An alternate index is a spanned record dataset.

a) true

b)false

6) A path is required so that an application program base cluster keys and retrieve alternate records.

a) true

b) false

7) Is it slower if you access a record through ALTERNATIVE INDEX as compared to Primary INDEX?

8) What could be the maximum number of the AIXs per base cluster?

9) Can AIX be defined over an ESDS, which does not have any Key?

10) What is an Alternate Index?

11) What are the steps used to create an Alternate Index?

12) What are the restrictions to be considered while creating an Alternate Index?


VSAM-handout

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