Performance Tuning Guide

This document identifies key performance benefits and tuning considerations when using Enterprise COBOL 6.4.

Throughout this information, “COBOL” or “Enterprise COBOL” refers to “IBM Enterprise COBOL for z/OS” or “IBM Enterprise COBOL Value Unit Edition for z/OS“.

First, this document gives an overview of the major performance features and options in COBOL 6 of the compiler, followed by performance improvements for several specific COBOL statements. Next, it provides tuning considerations for many compiler and runtime options that affect the performance of a COBOL application. Coding techniques to get the best performance are examined next with a special focus on any coding recommendations that have changed when using COBOL 6.

The final section examines some causes of increased program object size and studies the object size impact of the various new TEST suboptions as well as discussing the related issue of why PDSEs are required for programs compiled using COBOL 6.

The performance characteristics of COBOL 5 of the compiler are similar to COBOL 6. Except where otherwise noted, the information and recommendations in this document are also applicable to COBOL 5. Because the performance tuning changes required during migration from COBOL 5 to COBOL 6 are so small, recommendations and comparisons in this document assume that the reader is migrating from COBOL 4 of the compiler.

As the hardware evolves, COBOL 6 generated code is always improved. COBOL 4 generated code may improve as well, and in some cases, may improve even greater than COBOL 6. Thus, the apparent speedup of COBOL 6 generated code relative to COBOL 4 generated code is not monotonically increasing with each new generation of hardware.