COBOL I-O-CONTROL Section

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IDENTIFICATION DIVISION.
PROGRAM-ID. IO-CONTROL-DEMO.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT MASTER-FILE ASSIGN TO "MASTER.DAT"
           ORGANIZATION IS INDEXED
           ACCESS MODE IS DYNAMIC
           RECORD KEY IS MASTER-KEY
           FILE STATUS IS MASTER-STATUS.
    
    SELECT TRANSACTION-FILE ASSIGN TO "TRANS.DAT"
           ORGANIZATION IS SEQUENTIAL
           FILE STATUS IS TRANS-STATUS.
    
    SELECT REPORT-FILE ASSIGN TO "REPORT.TXT"
           ORGANIZATION IS SEQUENTIAL
           FILE STATUS IS REPORT-STATUS.
    
    SELECT BACKUP-FILE ASSIGN TO "BACKUP.DAT"
           ORGANIZATION IS SEQUENTIAL
           FILE STATUS IS BACKUP-STATUS.
 
I-O-CONTROL.
    *> Checkpoint every 1000 records for restart capability
    RERUN ON MASTER-FILE EVERY 1000 RECORDS
    RERUN ON REPORT-FILE EVERY END OF REEL
    
    *> Optimize memory usage by sharing areas
    SAME RECORD AREA FOR MASTER-FILE TRANSACTION-FILE
    SAME AREA FOR REPORT-FILE BACKUP-FILE
    
    *> Multiple file tape handling
    MULTIPLE FILE TAPE CONTAINS BACKUP-FILE REPORT-FILE
    
    *> Apply processing optimizations
    APPLY WRITE-ONLY ON REPORT-FILE
    APPLY LOCK-HOLDING ON MASTER-FILE.
 
DATA DIVISION.
FILE SECTION.
FD MASTER-FILE.
01 MASTER-RECORD.
   05 MASTER-KEY       PIC X(10).
   05 MASTER-DATA      PIC X(70).
 
FD TRANSACTION-FILE.
01 TRANSACTION-RECORD.
   05 TRANS-KEY        PIC X(10).
   05 TRANS-DATA       PIC X(50).
 
FD REPORT-FILE.
01 REPORT-RECORD      PIC X(80).
 
FD BACKUP-FILE.
01 BACKUP-RECORD      PIC X(80).
 
WORKING-STORAGE SECTION.
01 WS-FILE-STATUS.
   05 MASTER-STATUS    PIC XX.
   05 TRANS-STATUS     PIC XX.
   05 REPORT-STATUS    PIC XX.
   05 BACKUP-STATUS    PIC XX.
 
01 WS-COUNTERS.
   05 WS-RECORDS-PROCESSED  PIC 9(7) VALUE 0.
   05 WS-CHECKPOINT-COUNT   PIC 9(4) VALUE 0.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    PERFORM OPEN-FILES
    PERFORM PROCESS-TRANSACTIONS
    PERFORM CLOSE-FILES
    STOP RUN.
 
OPEN-FILES.
    OPEN I-O MASTER-FILE
    OPEN INPUT TRANSACTION-FILE
    OPEN OUTPUT REPORT-FILE
    OPEN OUTPUT BACKUP-FILE.
 
PROCESS-TRANSACTIONS.
    PERFORM UNTIL TRANS-STATUS = "10"
        READ TRANSACTION-FILE
            AT END CONTINUE
            NOT AT END PERFORM PROCESS-TRANSACTION
        END-READ
    END-PERFORM.
 
PROCESS-TRANSACTION.
    ADD 1 TO WS-RECORDS-PROCESSED
    
    *> Check for checkpoint interval
    IF FUNCTION MOD(WS-RECORDS-PROCESSED, 1000) = 0
       PERFORM CHECKPOINT-PROCESSING
    END-IF
    
    *> Process the transaction
    PERFORM UPDATE-MASTER-FILE
    PERFORM WRITE-REPORT-LINE
    PERFORM BACKUP-OPERATION.
 
CHECKPOINT-PROCESSING.
    ADD 1 TO WS-CHECKPOINT-COUNT
    DISPLAY "Checkpoint " WS-CHECKPOINT-COUNT 
            " at record " WS-RECORDS-PROCESSED
    
    *> The RERUN clause automatically handles checkpoint creation.
 
UPDATE-MASTER-FILE.
    MOVE TRANS-KEY TO MASTER-KEY
    READ MASTER-FILE
        KEY IS MASTER-KEY
        INVALID KEY PERFORM ADD-NEW-MASTER
        NOT INVALID KEY PERFORM UPDATE-EXISTING-MASTER
    END-READ.
 
CLOSE-FILES.
    CLOSE MASTER-FILE
    CLOSE TRANSACTION-FILE
    CLOSE REPORT-FILE
    CLOSE BACKUP-FILE.

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*> Production-level I-O-CONTROL example
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-MASTER ASSIGN TO "CUSTMAST"
           ORGANIZATION IS VSAM
           ACCESS MODE IS DYNAMIC
           RECORD KEY IS CUST-ID
           FILE STATUS IS CUST-STATUS.
    
    SELECT DAILY-TRANS ASSIGN TO "DAILYTRAN"
           ORGANIZATION IS SEQUENTIAL
           FILE STATUS IS TRANS-STATUS.
    
    SELECT AUDIT-LOG ASSIGN TO "AUDITLOG"
           ORGANIZATION IS SEQUENTIAL
           FILE STATUS IS AUDIT-STATUS.
    
    SELECT ERROR-FILE ASSIGN TO "ERRORLOG"
           ORGANIZATION IS SEQUENTIAL
           FILE STATUS IS ERROR-STATUS.
 
I-O-CONTROL.
    *> Comprehensive checkpoint strategy
    RERUN ON CUSTOMER-MASTER EVERY 2500 RECORDS
    RERUN ON AUDIT-LOG EVERY 5000 RECORDS
    RERUN ON ERROR-FILE EVERY END OF REEL
    
    *> Memory optimization for large volumes
    SAME RECORD AREA FOR CUSTOMER-MASTER DAILY-TRANS
    SAME AREA FOR AUDIT-LOG ERROR-FILE
    
    *> Tape handling for backup operations
    MULTIPLE FILE TAPE CONTAINS AUDIT-LOG ERROR-FILE
    
    *> Performance optimizations
    APPLY WRITE-ONLY ON AUDIT-LOG
    APPLY WRITE-ONLY ON ERROR-FILE
    APPLY LOCK-HOLDING ON CUSTOMER-MASTER.
 
*> Example with sort operations
I-O-CONTROL.
    RERUN ON SORT-INPUT EVERY 10000 RECORDS
    SAME SORT AREA FOR SORT-WORK-1 SORT-WORK-2
    SAME RECORD AREA FOR INPUT-FILE OUTPUT-FILE.
 
*> Complex multi-file processing
I-O-CONTROL.
    *> Different checkpoint intervals
    RERUN ON HIGH-VOLUME-FILE EVERY 1000 RECORDS
    RERUN ON MEDIUM-VOLUME-FILE EVERY 5000 RECORDS
    RERUN ON LOW-VOLUME-FILE EVERY END OF REEL
    
    *> Multiple area optimizations
    SAME RECORD AREA FOR FILE-A FILE-B FILE-C
    SAME AREA FOR REPORT-1 REPORT-2
    SAME SORT AREA FOR SORT-FILE-1 SORT-FILE-2
    
    *> Tape and processing options
    MULTIPLE FILE TAPE CONTAINS BACKUP-1 BACKUP-2 BACKUP-3
    APPLY WRITE-ONLY ON REPORT-1
    APPLY WRITE-ONLY ON REPORT-2
    APPLY LOCK-HOLDING ON MASTER-FILE.