LRECL Parameter

Purpose

The LRECL (Logical RECord Length) parameter defines the length, in bytes, of each logical record in a dataset. This parameter is crucial for proper data storage and retrieval, as it ensures that programs correctly interpret the boundaries between consecutive records.

Where LRECL is Used

• In DD statements as part of the DCB parameter
• In IDCAMS DEFINE commands (as RECORDSIZE)
• In TSO ALLOCATE commands
• In the DCB macro for assembler programs
• In dynamic allocation services (SVC 99)
• Within SMS data class definitions

Basic Syntax

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//ddname DD DSN=dataset.name,
//        DCB=(LRECL=nnnnn,...),
//        ...other parameters...

Where nnnnn is the length of each logical record in bytes.

VSAM Syntax (RECORDSIZE)

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//SYSIN DD *
  DEFINE CLUSTER (NAME(dataset.name)
         RECORDSIZE(average maximum)
         ...other parameters...)
/*

For VSAM datasets, LRECL is specified using the RECORDSIZE parameter, which takes both an average and maximum value.

LRECL Value Ranges

LRECL and RECFM Interaction

LRECL has specific meanings depending on the record format (RECFM) used:

Common LRECL Values

Usage Examples

Source Code Library

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//SRCLIB   DD DSN=USER.SOURCE.LIB,
//            DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(10,5,50)),
//            DCB=(RECFM=FB,LRECL=80,BLKSIZE=27920)

This example creates a partitioned dataset for source code with fixed-length 80-byte records, the standard format for source code libraries.

Print File

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//REPORT   DD DSN=USER.MONTHLY.REPORT,
//            DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(1,1)),
//            DCB=(RECFM=FBA,LRECL=133,BLKSIZE=13300)

This example defines a report file with ASA carriage control characters. The LRECL is 133 bytes: 1 byte for the ASA control character plus 132 bytes for the print line.

Variable-Length Log File

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//LOGFILE  DD DSN=USER.APPLICATION.LOG,
//            DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(5,2)),
//            DCB=(RECFM=VB,LRECL=1028,BLKSIZE=32760)

This example creates a log file with variable-length records. The LRECL is 1028 bytes, which means each record can contain up to 1024 bytes of actual data plus the 4-byte RDW.

VSAM KSDS Dataset

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//IDCAMS   EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
//SYSIN    DD *
  DEFINE CLUSTER (NAME(USER.CUSTOMER.FILE) -
         RECORDSIZE(200 500) -
         INDEXED -
         KEYS(16 0) -
         CYLINDERS(5 2))
/*

In this VSAM KSDS example, RECORDSIZE(200 500) specifies an average record length of 200 bytes and a maximum of 500 bytes.

TSO ALLOCATE Command

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ALLOC F(MYFILE) DA('USER.DATA.FILE') NEW SPACE(1,1) TRACKS -
      RECFM(FB) LRECL(80) BLKSIZE(27920)

This example shows specifying LRECL in a TSO ALLOCATE command, creating a new dataset with 80-byte fixed-length records.

LRECL Calculation Guidelines

• Fixed-Length Records: LRECL = actual data length
  • For print files with carriage control: LRECL = print line width + 1
• Variable-Length Records: LRECL = maximum data length + 4 (for RDW)
  • For print files with carriage control: LRECL = print line width + 1 + 4
• VSAM KSDS: Consider average and maximum record sizes
  • Average RECORDSIZE = typical record length
  • Maximum RECORDSIZE = largest possible record

Space Considerations

LRECL directly affects space requirements. For fixed-length records, calculating space is straightforward:

Common Issues and Troubleshooting

LRECL and Programming Languages

Different programming languages handle LRECL in specific ways:

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FD CUSTOMER-FILE
    RECORD CONTAINS 200 CHARACTERS
    BLOCK CONTAINS 0 RECORDS
    RECORDING MODE IS F.
01 CUSTOMER-RECORD.
    05 CUSTOMER-ID       PIC X(10).
    05 CUSTOMER-NAME     PIC X(30).
    ... (remaining fields)

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DCL CUSTOMER_FILE FILE RECORD INPUT ENV(FB BLKSIZE(6000) RECSIZE(200));
DCL 1 CUSTOMER_RECORD,
      2 CUSTOMER_ID     CHAR(10),
      2 CUSTOMER_NAME   CHAR(30),
      ... (remaining fields);

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CUSTFILE DCB   DSORG=PS,MACRF=(GM),DDNAME=CUSTDD,          X
               RECFM=FB,LRECL=200,BLKSIZE=6000

Best Practices

1. Use Appropriate LRECL Values: Choose LRECL based on the actual data requirements, not arbitrarily large values.
2. Consider Future Growth: Allow some room for expansion if fields might be added to records in the future.
3. Optimize for Storage: For fixed-length records, select an LRECL that minimizes wasted space.
4. Variable vs. Fixed Decision: Use variable-length records (V, VB) when record sizes vary significantly to save space.
5. VSAM Average and Maximum: For VSAM KSDS with RECORDSIZE, set realistic average and maximum values for optimal performance.
6. Consistent Definitions: Use the same LRECL value in all JCL and programs that access the same dataset.
7. Documentation: Document LRECL values and record layouts for all datasets to facilitate maintenance.
8. Track Capacity Awareness: Be mindful of track capacity limits when selecting LRECL values for efficient storage.

JES2 vs JES3 Considerations

LRECL is part of the data management system rather than the job entry subsystem, so it functions identically in both JES2 and JES3 environments. Both systems respect the same LRECL specifications in JCL.

Related Concepts

• RECFM Parameter - Record format specification that works with LRECL
• BLKSIZE Parameter - Block size, which should be a multiple of LRECL for fixed-length records
• DSORG Parameter - Dataset organization that affects LRECL requirements
• DCB Parameter - Data Control Block parameters that include LRECL
• DSNTYPE Parameter - Dataset type, which may impose constraints on LRECL