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Monday, July 27, 2009

VSAM Tutorial – How to create a ESDS and RRDS Cluster 

Q. How do you create an ESDS Object using JCL/Batch JOB?

An ESDS Cluster is a VSAM Dataset, which is similar to a sequential file. AnESDS Dataset has no Index Structure. Now, you might wonder, how to access the

records of an ESDS Cluster. Well, to access a record in an ESDS Cluster, you

need to know the exact address/physical location, where record lies on the Disk

Volume. It’s like saying, if you had a 1000 page book, and you wanted to access

the line having keyword laugh, you must know beforehand on which page no

(address) laugh is.

Thus, Records in ESDS Cluster are accessed by their Physical Address. This

address is called Relative Byte Address(RBA). ESDS works just like a stack/pile

of books. If you add records, they always get added to the top of the pile/

stack, i.e. the records get appended. Since the pile is too heavy, it is not

possible to insert records in between.

Here, I’ve shown how to create an empty ESDS Cluster using IDCAMS, DEFINE

CLUSTER Control statement.

----+----1----+----2----+----3----+----4----+----5----+----6----+----7--

//MYJOB004 JOB A123,QUASAR,NOTIFY=&SYSUID

//STEP01 EXEC PGM=IDCAMS

//SYSPRINT DD DSN=CAA0176.DEMO.JOBLOG,DISP=(OLD,KEEP,KEEP)

//SYSIN DD *

DEFINE CLUSTER( -

NAME(CAA0176.DEMO.ESDS) -

TRACKS(1 1) -

RECORDSIZE(80 80) -

NONINDEXED -

) -

DATA( -

NAME(CAA0176.DEMO.ESDS.DATA) -

)

/*

//

In the above example, I’ve created a new ESDS Cluster with the name CAA0176.

DEMO.ESDS. This ESDS Cluster will be allocated space(extents) in terms of 1

Primary Track and 1 Secondary Track. All records in this ESDS Cluster will be

of length 80 bytes. Moreover, since an ESDS Cluster does not have any key, wedon’t write KEYS keyword. Also, ESDS Cluster is specified using the option

 NONINDEXED.

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Since, it has on DATA Component, only the DATA Sub-parameter has been coded.

The ESDS Data component will have the name – CAA0176.DEMO.ESDS.DATA.

Q. How do you create an RRDS Object using a Batch JOB/JCL?

In a Relative Record Dataset, you must recall that each record is identified by

a Relative Record Number(RRN), which is nothing but the sequence number

relative to the first record.

No t e : As opposed t o KSDS, ESDS and RRDS suppo r t on l y f i xed l eng t h r eco r ds .

In RRDS, space is divided into fixed length slots. A slot can be either

completely vacant(does not contain a record) or completely full(contains a

record). Thus, you can add new records to empty slots, and delete existing

records from slots which are filled.

Let’s see a simple JCL to create an RRDS Cluster :

----+----1----+----2----+----3----+----4----+----5----+----6----+----7--

//MYJOB004 JOB A123,QUASAR,NOTIFY=&SYSUID

//STEP01 EXEC PGM=IDCAMS

//SYSPRINT DD DSN=CAA0176.DEMO.JOBLOG,DISP=(OLD,KEEP,KEEP)

//SYSIN DD *

DEFINE CLUSTER( -

NAME(CAA0176.DEMO.RRDS) -TRACKS(1 1) -

RECORDSIZE(80 80) -

NUMBERED -

REUSE -

) -

DATA( -

NAME(CAA0176.DEMO.RRDS.DATA) -

)

/*

//

RRDS is created on the same lines, like how we created an ESDS. The onlydifference being that since RRDS records are accessed by RRN(Sequence Number),

we must code NUMBERED inside the DEFINE CLUSTER AMS Command.

Technorati Tags: KSDS Cluster,ESDS,RRDS,Entry Sequenced Datset,Key-sequenced Dataset,Relative Record Dataset,Slots,Fixed Length,Relative Record Number,RRN,

Relative Byte Address,RBA,DEFINE CLUSTER,AMS,DATA,INDEX,KEYS,RECORDSIZE,TRACKS,NAME,NUMBERED,INDEXED Sequential,NONINDEXED,REUSE,CISZ,Mainframes,

IBM Mainframes 360,Mainframes 360,Quasar Chunawalla,VSAM,VSAM Tutorial,How to create ESDS and RRDS,ESDS Basics,RRDS Basics 

Posted by Quasar at Monday, July 27, 2009 

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Some Excerpts from Mainframes360

Q. What are the two broad types of Applications/Systems?

All application/systems are of 2 types

(i) Online Systems(Transaction Processing Systems)

(ii)Batch Processing Systems. Read more ...

Q. What is the DATA DIVSION? What are the different sections in the DATA DIVISION?

DATA DIVISION is used to describe the Input Output Storage areas and temporary storage areas. In other words, it’ll describe the

structure of the data being stored in Input Output Files, as well as in any temporary storage. Read more ...

Q. What are data-types? What are the basic data-types in COBOL?

Data-type is used to announce/declare to the MVS O/S, about the type of data you’re gonna store in a Storage Location, so that it

can estimate the storage space to be allocated and reserved for you data excusively. Read more ...

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In COBOL, one or more elementary data-items can be grouped together. For example, we can group EMP-NAME, EMP-SALARY and EMP-JDATE

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paragraph under the FILE SECTION. Remember, that FD paragraph is always coded in AREA A. Read more ...

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On Windows, to run a program, we simply click on the Executable File. In the same way, to run our COBOL Program on Mainframes, we

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Run JCL). Read more ...

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A Mainframe computer is used by large organisations for processing huge volumes of data e.g. census, consumer statistics, ERP and

financial transaction processing. Read more ...

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the latest machines in the Mainframe series is zSeries(pronounce Zee). Read more ...

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English? 

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IDENTIFICATION DIVISION is used to identify the COBOL Program to the system. It tells the... Read more ...

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Just like paragraphs in English, COBOL Divisions and Paragraphs must follow strict alignment rules. The way we indent paragraphs in

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PROGRAM-ID.

AUTHOR.

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Read more ...

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DIVISION. Read more ...

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Program on a Mainframe System?

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The WORKING-STORAGE SECTION is used to declare any fields or records that are not going to be used in input files, or output files,

but they are used to store the intermediate results of processing in a temporary storage area. Read more ...

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About Me

Quasar Chunawalla

Chennai, Tamil Nadu, India

Working at Tata Consultancy Services, Chennai

View my complete profile 

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