Three basic statements in a JCL.
- JOB statement, which identifies the start of the job, and information about the whole job, such as billing, run priority, and time & space limits.
- EXEC statement, which identifies the program to be executed in this step of the job, and information about the step.
- DD (Data Description) statements, which identify a data file to be used in a step, and detailed info about that file. DD statements can be in any order within the step.
How does override work on a JCL?
Without changing the actual procedure, we can add/modify contents of procedure.
There are two types of modifications:
on EXEC statement
on DD statement
- On EXEC statement, we can do following functions on EXEC statement in a procedure:
Adding parameter to an EXEC statement / all EXEC statement
PROCEDURE STATEMENT
//STEP10 EXEC PGM=COBPROG,TIME=3
PARAMETER ADDING
//MYSTEP EXEC PROC=MYPROC,REGION.STEP10=56K
(for single step)
REGION will be added to the STEP10 in MYPROC procedure
PARAMETER ADDING
//MYSTEP EXEC PROC=MYPROC,REGION=56K
(for single step)
If REGION is not available for any step in that procedure,
REGION will be added to all steps in procedure.
If REGION is available for any step in procedure, REGION value will be overriden.
//STEP10 EXEC PGM=COBPROG,TIME=3
PARAMETER ADDING
//MYSTEP EXEC PROC=MYPROC,REGION.STEP10=56K
(for single step)
REGION will be added to the STEP10 in MYPROC procedure
PARAMETER ADDING
//MYSTEP EXEC PROC=MYPROC,REGION=56K
(for single step)
If REGION is not available for any step in that procedure,
REGION will be added to all steps in procedure.
If REGION is available for any step in procedure, REGION value will be overriden.
Modify parameter on EXEC statements
PROCEDURE STATEMENT:
//STEP10 EXEC PGM=COBPROG,TIME=30
PARAMETER OVERRIDE:
//MYSTEP EXEC PROC=MYPROC,TIME.STEP1
Now Resulting TIME value for that step (in proc) is 40
//STEP10 EXEC PGM=COBPROG,TIME=30
PARAMETER OVERRIDE:
//MYSTEP EXEC PROC=MYPROC,TIME.STEP1
Now Resulting TIME value for that step (in proc) is 40
Nullifying the parameter value
PROCEDURE STATEMENT:
//STEP10 EXEC PGM=COBPROG,TIME=30
PARAMETER ADDING:
//MYSTEP EXEC PROC=MYPROC,TIME.STEP10=
Don’t give any value for that parameter, this will nullify the parameter value in procedure.
PROCEDURE STATEMENT:
//STEP10 EXEC PGM=COBPROG,TIME=30
PARAMETER ADDING:
//MYSTEP EXEC PROC=MYPROC,TIME.STEP10=
Don’t give any value for that parameter, this will nullify the parameter value in procedure.
On DD statement:
Syntax for add/modify DD statements in a procedure//name EXEC [PROC=]procedure-name//[procstepname].ddname DD parameter=value//We can do following functions on EXEC statement in a procedure using above syntax.Modify existing parameter on DD statements within a procedureAdd parameter to existing DD statement within a procedureAdd DD statement to a job stepNullify the effect of parameter on DD statement in a procedure.
What is the difference between Sequential Dataset and Partitioned Dataset?
• Any named collection of data is called a data set. A partitioned dataset consists of multiple files within one data structure. A sequential dataset consists of one file within a data structure.
• A partitioned dataset differs from a sequential dataset in that it has a directory of its members.
Whenever you refer to a member of a partitioned dataset, you include the member name in parentheses.
- Partitioned Dataset
2. it is advisable to never write directly to a partitioned dataset in your program
3. on DD statememt: DSN=userid.file(member)
4. call from editor: file(member)
PARTITIONED DATASET DSN='userid.data-set-name(member)'
______________
| DIRECTORY |
|-------------------|
| MEMBER1 |
|-------------------|
| MEMBER2 |
|-------------------|
| ----------- |
|-------------------|
| MEMBERn |
|-------------------|
|______________|
- Sequential Dataset
2. on DD statement: DSN=userid.file
3. call from editor: file
SEQUENTIAL DATASET DSN='userid.data-set-name'
______________
| |
| |
| |
| DATASET |
| |
| |
| |
|_____________|
What are the parameters needed to define a Data Set?
- The Data Sets used by a job step requires a Data Definition (or DD) statement.
- A simple DD statement requires the following:
o
DDNAME
o
Data Set Name (or
DSN)
o
Disposition (or
DISP) keyword.
Example://DDNAME DD DSN=dsname,DISP=(status,normal-term,abnormal-term)
In the preceding example the DDNAME in the JCL DD statement corresponds to the name used in the COBOL SELECT statement. The DSN= keyword specifies the fully-qualified MVS Data Set Name.
The DISP= keyword and parameter specifies the disposition as follows.
status
|
Description
|
OLD
|
The
dataset exists and this job step has exclusive use of the dataset.
|
SHR
|
The
dataset exists and other users and jobs can access the dataset, this is the
default
|
MOD
|
The
dataset should be kept and new records will be appended to the end of the
dataset. The dataset may or may not exist. If it does not exist then a data
set will be created.
|
NEW
|
The
dataset does not exist and will be created.
|
normal-term
|
Description
|
DELETE
|
Deletes
the data set at the end of the step
|
KEEP
|
Keeps
the data set.
|
CATLG
|
Places
the entry in the system catalog or user catalog. For a NEW data set this is
the default.
|
UNCATLG
|
Deletes
the entry from the system catalog or user catalog.
|
abnormal-term
|
Description
|
DELETE
|
Indicates
that the data set is to be deleted at the end of a job step.
|
KEEP
|
Indicates
that the data set is to be kept.
|
CATLG
|
Indicates
that the system should place an entry in the system or user catalog.
|
UNCATLG
|
Indicates
that the system is to delete the entry in the system or user catalog.
|
The DD statement for an Existing Data Sets:
o
The
DD name should be in positions 3-n (for a maximum of 8 characters) followed by
a space.
o
The DDNAME should correspond to the name defined in the program. For
example, with COBOL the name defined by the ASSIGN clause of the SELECT
statement.
The following is an example of a DD statement followed by a COBOL SELECT
statement with an ASSIGN clause.
//FILEIP DD DSN=MY.EXISTING.DATASET,DISP=SHR
The following is an example of a COBOL SELECT with an ASSIGN clause.
SELECT INPUT-FILE ASSIGN to FILEIP
//FILEOP DD DSN=MY.NEW.DATASET,DISP=(NEW,CATLG,DELETE),
// UNIT=SYSDA,
// VOL=SER=TST001,
// SPACE=(CYL,30,4),
// DCB=(RECFM=FB,LRECL=512,BLKSIZE=5120)
o UNIT Parameter:
In IBM Mainframe environment, all devices have an address assigned to them at the time
they added to the system. Devices can be referenced using these addresses. UNIT
parameter is used to specify this address.
In above example, FILEOP may reside on any of the devices which are grouped under the
symbolic name SYSDA will be accessed.
o VOL Parameter:
This parameter is used to identify the volume serial number on which dataset resides.
The VOL dataset is used with disk and tape datasets.
Sub parameters used with VOL parameter:
1. SER - Specification of serial number
2. REF - Referencing VOL specification from a prior step
3. PRIVATE - Allowing access to volume by single user
4. RETAIN - Inhibiting dismounting of volume until end of job
5. SEQ - Specification of sequence in which volumes are to be mounted
o SPACE Parameter:
The SPACE parameter is used to allocate space for datasets.
All new data sets on disk volumes must be allocated space.
Storage on disk volumes can be allocated in units of Cylinders (CYL), Tracks (TRK), Blocks (BLK) and Bytes.
Syntax:
SPACE=(CYL,(primary,secondary,directory),RLSE,CONTIG,MXIG,ROUND) Note: Instead of CYL, We can use TRK or BLK
The primary amount can be conservative, with the secondary amount providing a reserve.
The secondary amount provides for data set growth over time.
Meaning of Sub Parameter
1. PRIMARY - Primary storage to be allocated at the time of data set created
2. SECONDARY - Additional storage to be allocated, if primary storage is not sufficient. Up to 15 times only.
3. DIRECTORY - Space for recording of name and location of partitioned data sets
4. RLSE - Request for release of space previously allocated unused space after completion of job
5. CONTIG - Request for contiguous space
6. MXIG - Request for large area of contiguous space
7. ROUND - Request for entire cylinder for storage of data set
In this example, 30 cylinders are requested as primary space and 4 additional cylinders as secondary space.
Up to 15 extents of secondary space can be allocated.
To compute total space, formula is:
Total Space = (1 * primary) + (15 * secondary)
o DCB Parameter:
The Data Control Block (DCB) parameter is used to specify -
record format (RECFM), record length (LRECL) and block size (BLKSIZE).
Record Format (RECFM) can be:
1. Fixed (F)
2. Fixed-Block (FB)
3. Variable (V)
4. Variable-Block (VB)
5. Undefined length (U)
Record Length (LRECL) specifies the length of the record.
LRECL can range from 1 to 32760 bytes.
When you specified V for RECFM parameter, LRECL value is largest record in the file plus
4 bytes. These four bytes contain the actual length of each variable length record in the file
Depending on the record format, record length varies as follows:
1. Equal to the record length for fixed-length records
2. Equal to the size of the largest record plus the 4 bytes describing the record's size for variable-length records
3. Omit the LRECL for undefined records.
Block Size (BLKSIZE) specifies the block size if you wish to block records.
It must follow the following rules:
1. must be a multiple of LRECL for fixed-length records
2. must be equal to or greater than LRECL for variable-length records
3. must be as large as the longest block for undefined-length records
4. BLKSIZE can range from 1 to 32760 bytes
Use BLOCK CONTAINS 0 RECORDS in your FD (and BLKSIZE=0 in your JCL DCB
parameters) to allow the OS/390 operating system to optimize your block size. These two
changes ensure that the maximum number of records will be processed for a single file
input/output operation.
For an output dataset, if BLOCKSIZE is omitted from the FD section of the program or if
BLOCK CONTAINS 0 is specified, it will get the BLOCKSIZE defined in the DD
parameters (i.e. DCB) or dataset label of the file from the JCL..
It’s always better to write BLOCK CONTAINS 0 RECORDS / CHARACTERS in
COBOL program so that you can specify the BLKSIZE in JCL. Suppose there is a
requirement to change the BLKSIZE due to change in LRECL this will cause only change in
BLKSIZE in JCL. If you mention BLOCK contains N records in COBOL program, then it
is required to match with BLKSIZE in JCL also it would be required to change COBOL +
JCL both.
If you code BLKSIZE=0 in your DCB, the system will determine the most efficient block
size for space utilization.
MVS JCL Reviewer Part 2 can be viewed here.
The following is an example of a DD statement followed by a COBOL SELECT
statement with an ASSIGN clause.
//FILEIP DD DSN=MY.EXISTING.DATASET,DISP=SHR
The following is an example of a COBOL SELECT with an ASSIGN clause.
SELECT INPUT-FILE ASSIGN to FILEIP
The
DD statement for an Existing Data Sets:
o Other than the DD Name, DSN and DISP, new datasets also require the UNIT, VOL, SPACE and DCB parameters. //FILEOP DD DSN=MY.NEW.DATASET,DISP=(NEW,CATLG,DELETE),
// UNIT=SYSDA,
// VOL=SER=TST001,
// SPACE=(CYL,30,4),
// DCB=(RECFM=FB,LRECL=512,BLKSIZE=5120)
o UNIT Parameter:
In IBM Mainframe environment, all devices have an address assigned to them at the time
they added to the system. Devices can be referenced using these addresses. UNIT
parameter is used to specify this address.
In above example, FILEOP may reside on any of the devices which are grouped under the
symbolic name SYSDA will be accessed.
o VOL Parameter:
This parameter is used to identify the volume serial number on which dataset resides.
The VOL dataset is used with disk and tape datasets.
Sub parameters used with VOL parameter:
1. SER - Specification of serial number
2. REF - Referencing VOL specification from a prior step
3. PRIVATE - Allowing access to volume by single user
4. RETAIN - Inhibiting dismounting of volume until end of job
5. SEQ - Specification of sequence in which volumes are to be mounted
o SPACE Parameter:
The SPACE parameter is used to allocate space for datasets.
All new data sets on disk volumes must be allocated space.
Storage on disk volumes can be allocated in units of Cylinders (CYL), Tracks (TRK), Blocks (BLK) and Bytes.
Syntax:
SPACE=(CYL,(primary,secondary,directory),RLSE,CONTIG,MXIG,ROUND) Note: Instead of CYL, We can use TRK or BLK
The primary amount can be conservative, with the secondary amount providing a reserve.
The secondary amount provides for data set growth over time.
Meaning of Sub Parameter
1. PRIMARY - Primary storage to be allocated at the time of data set created
2. SECONDARY - Additional storage to be allocated, if primary storage is not sufficient. Up to 15 times only.
3. DIRECTORY - Space for recording of name and location of partitioned data sets
4. RLSE - Request for release of space previously allocated unused space after completion of job
5. CONTIG - Request for contiguous space
6. MXIG - Request for large area of contiguous space
7. ROUND - Request for entire cylinder for storage of data set
In this example, 30 cylinders are requested as primary space and 4 additional cylinders as secondary space.
Up to 15 extents of secondary space can be allocated.
To compute total space, formula is:
Total Space = (1 * primary) + (15 * secondary)
o DCB Parameter:
The Data Control Block (DCB) parameter is used to specify -
record format (RECFM), record length (LRECL) and block size (BLKSIZE).
Record Format (RECFM) can be:
1. Fixed (F)
2. Fixed-Block (FB)
3. Variable (V)
4. Variable-Block (VB)
5. Undefined length (U)
Record Length (LRECL) specifies the length of the record.
LRECL can range from 1 to 32760 bytes.
When you specified V for RECFM parameter, LRECL value is largest record in the file plus
4 bytes. These four bytes contain the actual length of each variable length record in the file
Depending on the record format, record length varies as follows:
1. Equal to the record length for fixed-length records
2. Equal to the size of the largest record plus the 4 bytes describing the record's size for variable-length records
3. Omit the LRECL for undefined records.
Block Size (BLKSIZE) specifies the block size if you wish to block records.
It must follow the following rules:
1. must be a multiple of LRECL for fixed-length records
2. must be equal to or greater than LRECL for variable-length records
3. must be as large as the longest block for undefined-length records
4. BLKSIZE can range from 1 to 32760 bytes
Use BLOCK CONTAINS 0 RECORDS in your FD (and BLKSIZE=0 in your JCL DCB
parameters) to allow the OS/390 operating system to optimize your block size. These two
changes ensure that the maximum number of records will be processed for a single file
input/output operation.
For an output dataset, if BLOCKSIZE is omitted from the FD section of the program or if
BLOCK CONTAINS 0 is specified, it will get the BLOCKSIZE defined in the DD
parameters (i.e. DCB) or dataset label of the file from the JCL..
It’s always better to write BLOCK CONTAINS 0 RECORDS / CHARACTERS in
COBOL program so that you can specify the BLKSIZE in JCL. Suppose there is a
requirement to change the BLKSIZE due to change in LRECL this will cause only change in
BLKSIZE in JCL. If you mention BLOCK contains N records in COBOL program, then it
is required to match with BLKSIZE in JCL also it would be required to change COBOL +
JCL both.
If you code BLKSIZE=0 in your DCB, the system will determine the most efficient block
size for space utilization.
MVS JCL Reviewer Part 2 can be viewed here.
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