Compiler Options that Affect Run-Time Performance

Compiler options, by far, have been the cause of a vast majority of the performance problems reported by customers. Many customers are not aware of the performance implications that many of the compiler options have at run time, especially the ARITH, AWO, DYNAM, FASTSRT, NUMPROC, OPTIMIZE, RENT, SSRANGE, TEST, THREAD, and TRUNC options. Let's look at each of these options to see how they might affect the performance of an application program.

• ARITH - EXTEND or COMPAT :
  The ARITH compiler option allows you to control the maximum number of digits allowed for numeric variables in your program.ARITH(EXTEND), the maximum number of digits is 31 - Slower. ARITH(COMPAT), the maximum number of digits is 18 - Faster
  
• AWO or NOAWO :
  APPLY WRITE-ONLY processing for physical sequential files with VB format.
  APPLY WRITE-ONLY , the file buffer is written to the output device when there is notenough space in the buffer for the next record.Without APPLY WRITE-ONLY, the file buffer is written to the output device when there is not enough space in the buffer for the maximum size record.
  If the application has a large variation in the size of the records to be written, using APPLY WRITE-ONLY can result in a performance savings since this will generally result in fewer I/O calls.
  NOAWO is the default.
  
• DATA(24) or DATA(31) :
  Specifies whether reentrant program data areas reside above or below the 16-MB line. With DATA(24) reentrant programs must reside below the 16-MB line. With DATA(31) reentrant programs can reside above the 16-MB line.
  DATA(31) is the default.
  
• DYNAM or NODYNAM :
  DYNAM ,Changes the behavior of CALL literal statements to load subprograms dynamically at run time. Call path length is longer - slower NODYNAM ,CALL literal statements cause subprograms to be statically link-edited in the load module. Call path length is - faster
  NODYNAM is the default.
  
• FASTSRT or NOFASTSRT :
  FASTSRT ,Specifies fast sorting by the IBM DFSORT licensed program. - FasterNOFASTSRT ,Specifies that Enterprise COBOL will do SORT or MERGE input/output. - Slower
  NOFASTSRT is the default
  
• NUMPROC - NOPFD, MIG, or PFD :
  Handles packed/zoned decimal signs as follows:
  NUMPROC(NOPFD), sign fix-up processing is done for all references to these numeric data items. NUMPROC(MIG), sign fix-up processing is done only for receiving fields (and not for sendingfields) of arithmetic and MOVE statements. NUMPROC(PFD), the compiler assumes that the data has the correct sign and bypasses this sign fix-up processing.
  For performance sensitive applications, NUMPROC(PFD) is recommended when possible.NUMPROC(NOPFD) is the default.
  
• OPTIMIZE(STD), OPTIMIZE(FULL), or NOOPTIMIZE :
  Optimizes the object program. OPTIMIZE has the suboptions of (STD/FULL). OPTIMIZE(FULL) provides improved runtime performance, over both the OS/VS COBOL and VS COBOL II OPTIMIZE option, because the compiler discards unused data items and does not generate code for any VALUE clauses for these data items.
  NOOPTIMIZE is generally used while a program is being developed when frequent compiles arenecessary. NOOPTIMIZE also makes it easier to debug a program since code is not moved;
  NOOPTIMIZE is the default.
  
• RENT or NORENT :
  Using the RENT compiler option causes the compiler to generate some additional code to ensure that the program is reentrant.
  On the average, RENT was equivalent to NORENT.
  RENT is the default.
  
• RMODE - AUTO, 24, or ANY :
  Allows NORENT programs to have RMODE(ANY).
  When using NORENT, the RMODE option controls where the WORKING-STORAGE will reside.With RMODE(24), the WORKING-STORAGE will be below the 16 MB line. With RMODE(ANY), theWORKING-STORAGE can be above the 16 MB line.
  RMODE(AUTO) is the default.
  
• SSRANGE or NOSSRANGE :
  SSRANGE - At run time, checks validity of subscript, index, and reference modification references. Its slower than NOSSRANGE.
  NOSSRANGE is the default.
  
• TEST or NOTEST :
  TEST - Produces object code usable by Debug Tool for the product. It is slower than NOTEST.
  NOTEST is the default.
  
• THREAD or NOTHREAD :
  THREAD -Enables a COBOL program for execution in a run unit with multiple POSIX threads or PL/I tasks. It is slower than NOTHREAD.
  NOTHREAD is the default.
  
• TRUNC - BIN, STD, or OPT :
  Truncates final intermediate results.
  TRUNC(STD) Truncates numeric fields according to PICTURE specification of the binary receiving field TRUNC(OPT) Truncates numeric fields in the most optimal way TRUNC(BIN) Truncates binary fields based on the storage they occupy
  On an average performance analysis -
  TRUNC(OPT) > TRUNC(STD) > TRUNC(BIN)
  TRUNC(STD) is the default.

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