Performance optimization is a critical aspect of COBOL programming, especially in enterprise environments where programs process large volumes of data and must meet strict throughput requirements. Optimizing COBOL programs requires understanding both the language features and the underlying hardware and software environment.
| Area | Impact | Common Techniques |
|---|---|---|
| I/O Operations | Often the biggest bottleneck | Buffering, blocking, access method selection |
| Table Handling | Critical for large datasets | Search algorithms, indexing, layout optimization |
| Arithmetic Operations | Important for calculation-heavy programs | Data type selection, expression optimization |
| Memory Usage | Affects both speed and capacity | Storage section usage, data organization |
| Compiler Options | Affects generated code efficiency | Optimization levels, hardware targeting |
Remember: Premature or unfocused optimization can lead to more complex code without significant performance benefits. Always measure before and after making changes to ensure your optimizations are effective.
Input/Output operations are often the most significant bottleneck in COBOL programs. Disk and network I/O are orders of magnitude slower than memory access and CPU operations, making I/O optimization one of the most effective ways to improve overall program performance.
One of the most effective I/O optimizations is to increase the number of records processed in a single physical I/O operation.
1// In JCL://INFILE DD DSN=MY.DATA.FILE,DISP=SHR,// DCB=(BLKSIZE=27920,BUFNO=5)// In COBOL:ENVIRONMENT DIVISION.INPUT-OUTPUT SECTION.FILE-CONTROL. SELECT CUSTOMER-FILE ASSIGN TO INFILE ORGANIZATION IS INDEXED ACCESS MODE IS RANDOM RECORD KEY IS CUSTOMER-ID.I-O-CONTROL. SAME RECORD AREA FOR CUSTOMER-FILE, ORDER-FILE.
Choosing optimal block sizes depends on your storage device characteristics. On modern disk systems, block sizes that are multiples of 4KB often perform well. For mainframe systems, consider using system-determined block sizes by specifying BLKSIZE=0.
Choose file organizations and access methods that match your program's access patterns:
| Access Pattern | Best File Organization | Explanation |
|---|---|---|
| Process every record in order | Sequential | Fastest for complete file processing |
| Frequent direct access by key | Indexed | Optimizes random access performance |
| Relative position access | Relative | Fast for positional access patterns |
| Mixed sequential and random | Indexed with DYNAMIC access | Provides flexibility without file reorganization |
1* For mostly sequential processing with occasional direct access:SELECT CUSTOMER-FILE ASSIGN TO CUSTDATA ORGANIZATION IS INDEXED ACCESS MODE IS DYNAMIC RECORD KEY IS CUSTOMER-ID.* In the procedure division:* Use sequential access for bulk processingOPEN INPUT CUSTOMER-FILEMOVE LOW-VALUES TO CUSTOMER-IDSTART CUSTOMER-FILE KEY >= CUSTOMER-ID INVALID KEY DISPLAY "Start error"END-STARTPERFORM UNTIL END-OF-FILE READ CUSTOMER-FILE NEXT AT END SET END-OF-FILE TO TRUE END-READ PERFORM PROCESS-CUSTOMER-RECORDEND-PERFORM* Switch to random access for specific lookupsMOVE '12345' TO CUSTOMER-IDREAD CUSTOMER-FILE INVALID KEY DISPLAY "Customer not found"END-READ
1* Bad: Inefficient repeated open/close and individual updatesPERFORM VARYING IDX FROM 1 BY 1 UNTIL IDX > 1000 OPEN I-O CUSTOMER-FILE MOVE CUSTOMER-IDS(IDX) TO CUSTOMER-ID READ CUSTOMER-FILE INVALID KEY CONTINUE END-READ ADD 1 TO CUSTOMER-COUNT REWRITE CUSTOMER-RECORD CLOSE CUSTOMER-FILEEND-PERFORM* Good: Single open, batched operations, single closeOPEN I-O CUSTOMER-FILEPERFORM VARYING IDX FROM 1 BY 1 UNTIL IDX > 1000 MOVE CUSTOMER-IDS(IDX) TO CUSTOMER-ID READ CUSTOMER-FILE INVALID KEY CONTINUE END-READ ADD 1 TO CUSTOMER-COUNT REWRITE CUSTOMER-RECORD * Commit every 100 records for reasonable checkpoint intervals IF FUNCTION MOD(IDX, 100) = 0 COMMIT END-IFEND-PERFORMCLOSE CUSTOMER-FILE
Sort operations can be resource-intensive. Optimize them with these techniques:
1* JCL for optimized sort://SORT EXEC PGM=SORT//SORTIN DD DSN=INPUT.FILE,DISP=SHR//SORTOUT DD DSN=OUTPUT.FILE,DISP=(NEW,CATLG),// SPACE=(CYL,(50,20),RLSE)//SORTWK01 DD UNIT=SYSDA,SPACE=(CYL,(100,50))//SORTWK02 DD UNIT=SYSDA,SPACE=(CYL,(100,50))//SORTWK03 DD UNIT=SYSDA,SPACE=(CYL,(100,50))//SYSIN DD * SORT FIELDS=(1,10,CH,A,11,8,CH,A) INCLUDE COND=(21,2,CH,EQ,C'AC')/** COBOL internal sort:SORT WORK-FILE ON ASCENDING KEY SORT-CUSTOMER-ID SORT-TRANSACTION-DATE USING INPUT-FILE OUTPUT PROCEDURE IS PROCESS-SORTED-RECORDS.
When working with databases (like DB2), consider these optimizations:
1* Instead of individual fetches:EXEC SQL DECLARE C1 CURSOR FOR SELECT CUSTOMER_ID, NAME, BALANCE FROM CUSTOMERS WHERE REGION_CODE = :REGION-CODEEND-EXEC.EXEC SQL OPEN C1 END-EXEC.PERFORM UNTIL SQLCODE NOT = 0 EXEC SQL FETCH C1 INTO :WS-CUSTOMER-ID, :WS-NAME, :WS-BALANCE END-EXEC IF SQLCODE = 0 PERFORM PROCESS-CUSTOMER END-IFEND-PERFORM* Better approach with array fetch:EXEC SQL DECLARE C1 CURSOR FOR SELECT CUSTOMER_ID, NAME, BALANCE FROM CUSTOMERS WHERE REGION_CODE = :REGION-CODEEND-EXEC.EXEC SQL OPEN C1 END-EXEC.EXEC SQL FETCH C1 INTO :WS-CUSTOMER-ID-ARRAY, :WS-NAME-ARRAY, :WS-BALANCE-ARRAY FOR 100 ROWSEND-EXEC.PERFORM VARYING IDX FROM 1 BY 1 UNTIL IDX > SQLERRD(3) OR SQLCODE < 0 PERFORM PROCESS-CUSTOMEREND-PERFORM
Tables (arrays) are fundamental data structures in COBOL programs. Optimizing table operations can significantly improve performance, especially for programs that process large datasets or reference tables frequently.
Choose the most appropriate search algorithm based on table characteristics:
| Search Method | Best Used When | Performance Characteristics |
|---|---|---|
| Sequential Search | Small tables, unsorted data | O(n) - Linear performance |
| Binary Search | Sorted tables | O(log n) - Much faster for large tables |
| Indexed Search | Tables with separate index array | Combines benefits of both methods |
| Hash Table | Frequent lookup by exact key | O(1) - Constant time regardless of size |
1* Sequential search implementation:PERFORM VARYING IDX FROM 1 BY 1 UNTIL IDX > TABLE-SIZE OR FOUND-FLAG = 'Y' IF TABLE-KEY(IDX) = SEARCH-KEY MOVE 'Y' TO FOUND-FLAG MOVE TABLE-DATA(IDX) TO RETURN-DATA END-IFEND-PERFORM* Binary search implementation:SET LOW-IDX TO 1SET HIGH-IDX TO TABLE-SIZEPERFORM UNTIL FOUND-FLAG = 'Y' OR LOW-IDX > HIGH-IDX COMPUTE MID-IDX = (LOW-IDX + HIGH-IDX) / 2 IF TABLE-KEY(MID-IDX) = SEARCH-KEY MOVE 'Y' TO FOUND-FLAG MOVE TABLE-DATA(MID-IDX) TO RETURN-DATA ELSE IF TABLE-KEY(MID-IDX) > SEARCH-KEY COMPUTE HIGH-IDX = MID-IDX - 1 ELSE COMPUTE LOW-IDX = MID-IDX + 1 END-IF END-IFEND-PERFORM
COBOL provides built-in SEARCH verb for table operations, which can be optimized:
101 PRODUCT-TABLE. 05 PRODUCT-ENTRY OCCURS 1000 TIMES ASCENDING KEY IS PRODUCT-CODE INDEXED BY PROD-IDX. 10 PRODUCT-CODE PIC X(8). 10 PRODUCT-DESC PIC X(30). 10 PRODUCT-PRICE PIC 9(5)V99.* Using SEARCH ALL for binary searchSEARCH ALL PRODUCT-ENTRY AT END DISPLAY "Product not found: " SEARCH-PRODUCT-CODE WHEN PRODUCT-CODE(PROD-IDX) = SEARCH-PRODUCT-CODE MOVE PRODUCT-DESC(PROD-IDX) TO OUTPUT-DESC MOVE PRODUCT-PRICE(PROD-IDX) TO OUTPUT-PRICEEND-SEARCH
Important: Tables using SEARCH ALL must be sorted on the specified key field. The compiler does not sort the table for you - you must ensure it's properly sorted.
1* Optimized structure for frequently accessed fields01 CUSTOMER-TABLE. 05 CUSTOMER-COUNT PIC 9(5) COMP. 05 CUSTOMER-ENTRY OCCURS 1 TO 50000 TIMES DEPENDING ON CUSTOMER-COUNT INDEXED BY CUST-IDX. 10 CUSTOMER-ID PIC X(10). *> Most frequently accessed - first 10 CUSTOMER-TYPE PIC X(1). *> Often used in processing logic 10 CUSTOMER-STATS. 15 TOTAL-ORDERS PIC 9(5) COMP-3. 15 TOTAL-VALUE PIC 9(9)V99 COMP-3. 10 CUSTOMER-DETAILS. *> Less accessed details grouped 15 CUSTOMER-NAME PIC X(30). 15 CUSTOMER-ADDR PIC X(50). 15 CUSTOMER-PHONE PIC X(15).
How tables are loaded and initialized can significantly impact performance:
1* Efficient bulk loading from a fileOPEN INPUT REFERENCE-FILEMOVE ZERO TO TABLE-COUNTPERFORM UNTIL END-OF-FILE READ REFERENCE-FILE AT END SET END-OF-FILE TO TRUE NOT AT END ADD 1 TO TABLE-COUNT MOVE REF-KEY TO TABLE-KEY(TABLE-COUNT) MOVE REF-DATA TO TABLE-DATA(TABLE-COUNT) END-READEND-PERFORMCLOSE REFERENCE-FILE* External table shared between programs01 REFERENCE-TABLE EXTERNAL. 05 TABLE-LOADED-FLAG PIC X. 05 TABLE-ENTRY OCCURS 1000 TIMES INDEXED BY REF-IDX. 10 TABLE-CODE PIC X(10). 10 TABLE-DESC PIC X(30).
For very large tables, consider implementing caching strategies:
1* Simple last-item cache01 CACHE-AREA. 05 CACHE-KEY PIC X(10). 05 CACHE-DATA PIC X(100). 05 CACHE-VALID-FLAG PIC X VALUE 'N'. 88 CACHE-VALID VALUE 'Y'. 88 CACHE-INVALID VALUE 'N'.* Check cache before searching main tableLOOKUP-WITH-CACHE. IF CACHE-VALID AND LOOKUP-KEY = CACHE-KEY MOVE CACHE-DATA TO RETURN-DATA ELSE PERFORM MAIN-TABLE-LOOKUP MOVE LOOKUP-KEY TO CACHE-KEY MOVE FOUND-DATA TO CACHE-DATA IF FOUND-FLAG = 'Y' SET CACHE-VALID TO TRUE ELSE SET CACHE-INVALID TO TRUE END-IF END-IF
While COBOL is often associated with business data processing rather than intensive calculations, many COBOL programs perform significant arithmetic operations. Optimizing these operations can yield substantial performance improvements, especially in calculation-heavy programs.
Choosing the right data types for numeric fields is crucial for performance:
| Data Type | Best Used For | Performance Characteristics |
|---|---|---|
| DISPLAY (Default) | I/O operations, human-readable output | Slowest for calculations, requires conversion |
| COMP / BINARY | Counters, indexes, integers | Fast for basic arithmetic, efficient storage |
| COMP-3 / PACKED-DECIMAL | Business calculations with decimals | Good balance of storage efficiency and performance |
| COMP-1 / COMP-2 (Floating Point) | Scientific calculations, very large ranges | Fast for complex math, but potential precision issues |
123456789101112131415* Optimized data types for different uses 01 CALCULATION-FIELDS. * For counters and indices (frequently incremented) 05 RECORD-COUNT PIC 9(8) COMP. 05 LOOP-INDEX PIC 9(4) COMP. * For business calculations with decimals 05 INVOICE-TOTAL PIC 9(9)V99 COMP-3. 05 TAX-AMOUNT PIC 9(7)V99 COMP-3. * For display formatting (not used in calculations) 05 FORMATTED-AMOUNT PIC Z,ZZZ,ZZ9.99. * For scientific calculations 05 STATISTICAL-FACTOR PIC 9(9)V9(9) COMP-2.
1234567891011121314151617* Less efficient - mixed types causing conversions COMPUTE DISPLAY-TOTAL = NUMERIC-COUNT * 5.25 + TAX-RATE * (SUBTOTAL - DISCOUNT-AMT) * More efficient - consistent types, intermediate results MULTIPLY NUMERIC-COUNT BY UNIT-PRICE GIVING ITEM-TOTAL SUBTRACT DISCOUNT-AMT FROM SUBTOTAL GIVING DISCOUNTED-AMOUNT MULTIPLY DISCOUNTED-AMOUNT BY TAX-RATE GIVING TAX-AMOUNT ADD ITEM-TOTAL TO TAX-AMOUNT GIVING DISPLAY-TOTAL * Even better for repeated calculations - precalculate COMPUTE TAX-FACTOR = 1 + TAX-RATE PERFORM VARYING IDX FROM 1 BY 1 UNTIL IDX > ITEM-COUNT COMPUTE ITEM-TOTAL(IDX) = ITEM-QTY(IDX) * ITEM-PRICE(IDX) COMPUTE TAXABLE-AMT(IDX) = ITEM-TOTAL(IDX) - ITEM-DISCOUNT(IDX) COMPUTE FINAL-PRICE(IDX) = TAXABLE-AMT(IDX) * TAX-FACTOR END-PERFORM
Managing precision and rounding efficiently:
123456789101112131415161718* Less efficient - unnecessary ROUNDED and SIZE ERROR checks COMPUTE RESULT ROUNDED = TOTAL-A / DIVISOR-B ON SIZE ERROR PERFORM ERROR-ROUTINE END-COMPUTE * More efficient - only use when needed IF DIVISOR-B = ZERO PERFORM DIVISION-BY-ZERO-ERROR ELSE COMPUTE RESULT = TOTAL-A / DIVISOR-B END-IF * Integer scaling for performance-critical code * Instead of using PIC 9(7)V99, scale by 100 * This changes $1234.56 to 123456 COMPUTE INTEGER-RESULT = SCALED-VALUE-A + SCALED-VALUE-B COMPUTE DISPLAY-RESULT = INTEGER-RESULT / 100
Using intrinsic functions effectively for calculations:
1234567891011121314151617181920* Less efficient - custom implementations COMPUTE PI = 3.14159 COMPUTE RESULT = AMOUNT * (PI / 180) * More efficient - intrinsic functions COMPUTE RESULT = AMOUNT * FUNCTION SIN(ANGLE * FUNCTION PI / 180) * Less efficient - manual loop MOVE ZERO TO ARRAY-SUM MOVE ZERO TO MAX-VALUE PERFORM VARYING IDX FROM 1 BY 1 UNTIL IDX > ARRAY-SIZE ADD ARRAY-ELEMENT(IDX) TO ARRAY-SUM IF ARRAY-ELEMENT(IDX) > MAX-VALUE MOVE ARRAY-ELEMENT(IDX) TO MAX-VALUE END-IF END-PERFORM * More efficient - intrinsic functions COMPUTE ARRAY-SUM = FUNCTION SUM(ARRAY-ELEMENT(1:ARRAY-SIZE)) COMPUTE MAX-VALUE = FUNCTION MAX(ARRAY-ELEMENT(1:ARRAY-SIZE))
Optimizing calculation-intensive loops:
1234567891011121314151617* Less efficient - invariant calculation inside loop PERFORM VARYING ROW-IDX FROM 1 BY 1 UNTIL ROW-IDX > ROW-MAX PERFORM VARYING COL-IDX FROM 1 BY 1 UNTIL COL-IDX > COL-MAX COMPUTE CONVERSION-FACTOR = BASE-RATE * (1 + TAX-RATE) COMPUTE CELL-VALUE(ROW-IDX, COL-IDX) = RAW-VALUE(ROW-IDX, COL-IDX) * CONVERSION-FACTOR END-PERFORM END-PERFORM * More efficient - invariant calculation outside loop COMPUTE CONVERSION-FACTOR = BASE-RATE * (1 + TAX-RATE) PERFORM VARYING ROW-IDX FROM 1 BY 1 UNTIL ROW-IDX > ROW-MAX PERFORM VARYING COL-IDX FROM 1 BY 1 UNTIL COL-IDX > COL-MAX COMPUTE CELL-VALUE(ROW-IDX, COL-IDX) = RAW-VALUE(ROW-IDX, COL-IDX) * CONVERSION-FACTOR END-PERFORM END-PERFORM
Efficient memory usage not only reduces the resources required by a program but can also improve performance by optimizing data access patterns and reducing overhead. COBOL provides various mechanisms for controlling memory allocation and usage.
Choose the most appropriate storage section for variables:
| Storage Section | Best Used For | Memory Characteristics |
|---|---|---|
| WORKING-STORAGE | Program-wide variables, values that persist between calls | Allocated once, retains values between invocations |
| LOCAL-STORAGE | Subprogram variables that don't need to persist | Fresh allocation each time, automatic cleanup |
| LINKAGE SECTION | Parameters passed from calling program | References memory owned by caller, no allocation |
12345678910111213141516171819202122232425262728* Optimal use of storage sections IDENTIFICATION DIVISION. PROGRAM-ID. CALCULATE-STATS. DATA DIVISION. * For program-wide configuration that persists between calls WORKING-STORAGE SECTION. 01 PROGRAM-CONSTANTS. 05 PI-VALUE PIC 9(1)V9(5) VALUE 3.14159. 05 MAX-ITERATIONS PIC 9(5) VALUE 10000. 05 CALL-COUNTER PIC 9(8) VALUE ZERO. * For variables that need fresh allocation each time LOCAL-STORAGE SECTION. 01 CALCULATION-WORK-AREAS. 05 TEMP-RESULT PIC 9(9)V99. 05 LOOP-COUNTER PIC 9(5). 05 INTERMEDIATE-SUMS PIC 9(9)V99 OCCURS 100 TIMES. * For data passed from the caller LINKAGE SECTION. 01 INPUT-DATA. 05 DATA-COUNT PIC 9(5). 05 DATA-ELEMENTS PIC 9(9)V99 OCCURS 1 TO 1000 TIMES DEPENDING ON DATA-COUNT. 01 RESULT-DATA. 05 MEAN-VALUE PIC 9(9)V99. 05 STD-DEVIATION PIC 9(9)V99.
Using LOCAL-STORAGE for large temporary work areas in frequently called subprograms can significantly improve performance by avoiding the need to explicitly initialize variables on each call.
1234567891011121314151617181920212223* Efficient memory organization 01 CUSTOMER-RECORD. * Fixed-length header with frequently accessed fields 05 CUSTOMER-ID PIC X(10). 05 RECORD-TYPE PIC X. 05 RECORD-STATUS PIC X. * Variable-length data that adapts to actual size 05 ADDRESS-COUNT PIC 9(2) COMP. 05 ADDRESSES OCCURS 1 TO 10 TIMES DEPENDING ON ADDRESS-COUNT. 10 ADDRESS-TYPE PIC X. 10 ADDRESS-LINE-1 PIC X(30). 10 ADDRESS-LINE-2 PIC X(30). 10 CITY PIC X(20). 10 STATE PIC X(2). 10 ZIP-CODE PIC X(10). * Ensure binary fields are aligned for efficient access 05 FILLER PIC X. 05 NUMERIC-VALUES. 10 TOTAL-ORDERS PIC 9(8) COMP. 10 TOTAL-AMOUNT PIC 9(12)V99 COMP-3.
Modern COBOL supports dynamic memory allocation and management:
12345678910111213141516171819202122232425262728* Dynamic memory allocation with ALLOCATE/FREE 01 CUSTOMER-PTR USAGE POINTER. 01 CUSTOMER-STRUCT. 05 CUSTOMER-ID PIC X(10). 05 CUSTOMER-NAME PIC X(30). 05 BALANCE PIC 9(9)V99 COMP-3. * Allocate memory dynamically ALLOCATE CUSTOMER-STRUCT RETURNING CUSTOMER-PTR SET ADDRESS OF CUSTOMER-DATA TO CUSTOMER-PTR * Use the allocated memory MOVE "1234567890" TO CUSTOMER-ID OF CUSTOMER-DATA MOVE "JOHN DOE" TO CUSTOMER-NAME OF CUSTOMER-DATA MOVE 1250.00 TO BALANCE OF CUSTOMER-DATA * Later, free the memory when done FREE CUSTOMER-PTR * Using unbounded tables for dynamic arrays 01 DYNAMIC-TABLE. 05 RECORD-COUNT PIC 9(9) COMP. 05 TABLE-DATA OCCURS UNBOUNDED DEPENDING ON RECORD-COUNT INDEXED BY DATA-IDX. 10 DATA-ELEMENT PIC X(100). * Set the size based on actual needs MOVE 1000 TO RECORD-COUNT
Techniques to minimize the overall memory usage:
1234567891011121314151617181920212223* Space-efficient data definitions 01 CUSTOMER-RECORD. * Use minimal field sizes 05 CUST-TYPE PIC X. 88 INDIVIDUAL VALUE "I". 88 BUSINESS VALUE "B". * Pack multiple indicators into a single byte 05 STATUS-FLAGS PIC X. 88 ACTIVE VALUE X"80". 88 CREDIT-HOLD VALUE X"40". 88 TAX-EXEMPT VALUE X"20". 88 VIP-CUSTOMER VALUE X"10". * Efficient numeric storage 05 ACCOUNT-BALANCE PIC 9(9)V99 COMP-3. * Shared data between programs 01 GLOBAL-SETTINGS EXTERNAL. 05 COMPANY-NAME PIC X(30). 05 TAX-RATES. 10 STATE-TAX PIC V999 VALUE .075. 10 COUNTY-TAX PIC V999 VALUE .025.
Optimize how your program accesses memory:
123456789101112131415161718192021222324252627282930313233343536373839404142* Efficient sequential access pattern SORT WORK-FILE ON ASCENDING KEY SORT-CUSTOMER-ID USING INPUT-FILE GIVING TEMP-FILE * Process sorted data sequentially for better cache efficiency OPEN INPUT TEMP-FILE PERFORM UNTIL END-OF-FILE READ TEMP-FILE AT END SET END-OF-FILE TO TRUE NOT AT END PERFORM PROCESS-RECORD END-READ END-PERFORM CLOSE TEMP-FILE * Batch processing for memory efficiency OPEN INPUT LARGE-FILE OPEN OUTPUT RESULT-FILE PERFORM UNTIL END-OF-LARGE-FILE * Read a batch of records PERFORM VARYING BATCH-IDX FROM 1 BY 1 UNTIL BATCH-IDX > BATCH-SIZE OR END-OF-LARGE-FILE READ LARGE-FILE AT END SET END-OF-LARGE-FILE TO TRUE NOT AT END MOVE INPUT-RECORD TO BATCH-RECORD(BATCH-IDX) ADD 1 TO RECORD-COUNT END-READ END-PERFORM * Process the batch PERFORM PROCESS-BATCH * Write results PERFORM WRITE-BATCH-RESULTS END-PERFORM CLOSE LARGE-FILE CLOSE RESULT-FILE
Modern COBOL compilers provide numerous options to optimize the generated code. Understanding these options and their effects is essential for maximizing program performance without changing the source code.
| Option | Effect | When to Use |
|---|---|---|
| OPTIMIZE | Controls the level of optimization (0-2) | Production code, set to highest level (2) for best performance |
| ARCH | Targets specific hardware architecture | When you know the target processor model |
| TUNE | Optimizes for specific processor | When program runs on specific hardware |
| NUMPROC | Controls handling of numeric signs | NUMPROC(PFD) for best performance |
| SSRANGE | Checks subscript ranges at runtime | Debugging (YES) or production (NO) |
| TRUNC | Controls binary field truncation | TRUNC(BIN) for best performance |
| THREAD | Enables multi-threading capability | For programs that run in threaded environments |
| RENT | Makes code reentrant (reusable) | Multi-user environments and shared modules |
12345// JCL example with optimized compiler options //COBOL EXEC PGM=IGYCRCTL,REGION=0M, // PARM='OPTIMIZE(2),ARCH(13),TUNE(13), // NUMPROC(PFD),SSRANGE(NO),TRUNC(BIN), // RENT,NOTEST'
The OPTIMIZE compiler option has different levels with varying effects:
Optimizations performed at higher levels include:
Higher optimization levels can sometimes make debugging more difficult since the relationship between source code and generated instructions becomes less direct.
ARCH and TUNE options optimize code for specific hardware:
For IBM mainframes, common ARCH values include:
Setting ARCH to match your target hardware can provide significant performance improvements by utilizing the latest processor features.
Different compiler options are appropriate for different phases:
| Development/Debugging | Production/Performance |
|---|---|
| OPTIMIZE(0) | OPTIMIZE(2) |
| TEST | NOTEST |
| SSRANGE(YES) | SSRANGE(NO) |
| NUMCHECK | NONUMCHECK |
| DEBUG | NODEBUG |
123456789// Development phase compiler options //COBOL EXEC PGM=IGYCRCTL, // PARM='OPTIMIZE(0),TEST(SOURCE),SSRANGE(YES), // NUMCHECK(PAC,ZON,BIN),DEBUG' // Production phase compiler options //COBOL EXEC PGM=IGYCRCTL, // PARM='OPTIMIZE(2),NOTEST,SSRANGE(NO), // NONUMCHECK,NODEBUG,STGOPT'
Additional options that can impact performance:
1234// Additional optimization options //COBOL EXEC PGM=IGYCRCTL, // PARM='OPTIMIZE(2),STGOPT,AFP(NOVOLATILE), // HGPR(PRESERVE),FASTSRT'
To determine the effectiveness of compiler optimizations:
Remember that compiler optimization should be considered as part of a comprehensive performance tuning strategy that includes algorithm improvements, I/O optimization, and memory management.
1. Which technique is most effective for optimizing I/O operations in COBOL programs?
2. What is the most efficient way to search a table in COBOL?
3. Which compiler option can have the greatest positive impact on COBOL program performance?
4. Which of the following arithmetic optimizations is generally most effective in COBOL?
5. Which memory optimization technique generally provides the best performance benefits?