Writing Efficient and Portable Macros

Keeping Efficiency in Perspective

Efficiency is an elusive thing, hard to quantify and harder still to define. What works with one application might not work with another, and what is efficient on one host environment might be inefficient on a different system. However, there are some generalities that you should keep in mind.

Usually, efficiency issues are discussed in terms of CPU cycles, elapsed time, I/O hits, memory usage, disk storage, and so on. This section does not give benchmarks in these terms because of all the variables involved. A program that runs only once needs different tuning than a program that runs hundreds of times. An application running on a mainframe has different hardware parameters than an application developed on a desktop PC. You must keep efficiency in perspective with your environment.

There are different approaches to efficiency, depending on what resources you want to conserve. Are CPU cycles more critical than I/O hits? Do you have lots of memory but no disk space? Taking stock of your situation before deciding how to tune your programs is a good idea.

The area of efficiency most affected by the SAS macro facility is human efficiency -- how much time is required to both develop and maintain a program. Autocall macros are particularly important in this area because the autocall facility provides code reusability. Once you develop a macro that performs a task, you can save it and use it not only in the application you developed it for, but also in future applications without any further work. A library of reusable, immediately callable macros is a boon to any application development team.

The Stored Compiled Macro Facility (described in Storing and Reusing Macros) might reduce execution time by enabling previously compiled macros to be accessed during different SAS jobs and sessions. But it is a tool that is efficient only for production applications, not during application development. So the efficiency techniques you choose depend not only on your hardware and personnel situation, but also on the stage you have reached in your application development process.

Also, remember that incorporating macro code into a SAS application does not automatically make the application more efficient. When designing a SAS application, concentrate on making the basic SAS code that macros generate more efficient. There are many sources for information about efficient SAS code, including SAS Programming Tips: A Guide to Efficient SAS Processing.

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