Easytrieve Relative File Processing

FILE RELATIVE Declaration

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FILE SLOTTAB RELATIVE UPDATE FB(40 1800)
 
DEFINE SLOTTAB
  SLOT-RRN    9   1    * relative record number field
  SLOT-ACTIVE A   1   10
  SLOT-DATA   A  25   11

RELATIVE tells Easytrieve the access method addresses records by number. UPDATE permits rewriting slot contents. FB record length must match RRDS slot size from IDCAMS. MAXRRN in cluster define caps valid slot numbers; referencing beyond max produces errors. Some shops number slots starting at 1; verify whether your RRDS uses 1-based or 0-based convention in operations documentation.

RRDS Versus KSDS Versus ESDS

Choose RELATIVE when application logic already computes an integer slot index. Choose INDEXED when operators search by business key. Mixing metaphors—storing employee ID as RRDN without contiguous numbering—wastes space and confuses maintainers.

Reading and Writing Slots

Set the relative record number field to the slot you need, then issue READ file-name for retrieval or WRITE/PUT paths for update per Broadcom release documentation. STATUS captures FILE-STATUS when I/O fails—invalid slot, not defined, or authority. After READ, test whether SLOT-ACTIVE or equivalent flag shows the slot was ever written; empty slots may read as zeros when RESET zeros numeric fields on input.

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COMPUTE SLOT-RRN = TABLE-INDEX + 1
READ SLOTTAB STATUS
IF NOT SLOTTAB
   MOVE 'EMPTY' TO MSG
   EXIT
END-IF
IF SLOT-ACTIVE EQ 'N'
   MOVE 'UNUSED SLOT' TO MSG
   EXIT
END-IF

RESET and Empty Slots

RESET on FILE controls whether numeric fields zero when records load into buffers. Empty RRDS slots never written may return low-values or zeros; character fields may be blank or garbage if never initialized. Application designs include active flag, version stamp, or checksum in each slot so readers distinguish real data from never-used cells. Maintenance jobs preformat slots with active N before production load.

Sequential Browse With GET

GET on RELATIVE files can walk slots in relative order—scan entire table for active entries without knowing keys in advance. JOB INPUT on RELATIVE with UPDATE supports batch walk-and-update similar to indexed browse. EOF marks end of allocated slot range. Combine GET scan with IF SLOT-ACTIVE to skip holes efficiently.

JCL and Allocation

RRDS clusters define slot size and maximum records at IDCAMS time. DD allocation matches other VSAM types: DSN, DISP=SHR or OLD, AMP='AMORG=VSAM'. Growing RRDS may require redefinition offline—Easytrieve does not expand MAXRRN at runtime. Plan slot capacity with capacity management before coding RELATIVE FILE.

UPDATE Maintenance Patterns

Slot update jobs READ or GET HOLD slot, MOVE new SLOT-DATA, WRITE back. DELETE in keyed sense may mean marking SLOT-ACTIVE N rather than physical remove—RRDS slots remain allocated. Batch refresh jobs zero slots then reload from sequential input using computed RRN from input record number field.

Relative Files on Non-z/OS Platforms

Broadcom documents RELATIVE for platform indexed relatives outside VSAM. FILE rules and verb availability follow the platform supplement. Mainframe RRDS remains the focus of this tutorial series; verify release notes when porting RELATIVE programs between environments.

Common Relative Mistakes

• RRN outside 1..MAXRRN range.
• Treating uninitialized slot as valid business data.
• Using INDEXED READ against RRDS DD.
• Slot size mismatch between FILE FB and IDCAMS.
• UPDATE missing on slot rewrite job.
• Confusing relative record number with KSDS key value.

Explain It Like I'm Five

A relative file is a row of numbered mailboxes. Mailbox 1, mailbox 2, up to the last number the building installed. You do not search by name—you say "open mailbox 17" and look inside. Empty mailboxes might look blank or full of zeros until someone puts real mail there. UPDATE means you may replace the mail in a mailbox that already exists. You cannot magically add mailbox 500 if the building only built 200 boxes—that is MAXRRN.

Exercises

1. Declare RELATIVE FILE with active flag and data fields.
2. Write logic that READs one slot by computed RRN and handles empty active flag.
3. Compare RRDS versus KSDS for a 10,000-row table keyed by contiguous IDs.
4. List JCL and IDCAMS items to verify before first RRDS test run.
5. Sketch GET loop that scans all slots and PRINT only active ones.