One of the most intriguing aspects of writing code for clients that have huge/enormous databases is that you get to test the performance of RPG IV features. One feature that continues to annoy me is the fact that a character return value from a procedure that is VARYING sucks from a performance perspective.
For example:
D inString 32766A VALUE Varying
Seems logical, right? If you convert a character string to uppercase, you want to return the same size/length value to the caller, so the following would be a valid call to TOUPPER:
C eval CompName = ToUpper(CompName)
Obviously, this converts the COMPNAME field to all uppercase letters. But what we don't see is that that the long 32K return value is causing a performance issue. Even through it is varying, the system still returns the entire 32K of data and throws away the extra bytes, a waste of resources.
When the load is light or when TOUPPER is called only once or perhaps a few times per transaction, then this overhead isn't important. But when you call TOUPPER hundreds, thousands, or perhaps millions of times, there could be problems.
To resolve this problem, you need to avoid returning a value and instead pass an additional parameter that is updated.
For example:
D InString 32766A Const Varying
D OutString 32766A OPTIONS(*VARSIZE)
The second parameter now becomes the target of the conversion, and the OPTIONS(*VARSIZE) allows you to pass a parameter whose length is 1 to 32766 bytes. You simply use %LEN(InString) inside the subprocedure to determine how much data was actually passed to your subprocedure. Then, be sure to "touch" only that many characters in the OUTSTRING parameter.
One problem that arises using this technique, however, is that you can no longer use a VARYING field to receive the output, and this does present restriction. One solution is to have two subprocedures, one that supports fixed-length output and a second one that supports varying-length fields.
For example:
D InString 32766A Const Varying
D OutString 32766A VARYING OPTIONS(*VARSIZE)
Bob Cozzi has been programming in RPG since 1978. Since then, he has written many articles and several books, including The Modern RPG Language--the most widely used RPG reference manual in the world. Bob is also a very popular speaker at industry events such as RPG World and is the author of his own Web site and of the RPG ToolKit, an add-on library for RPG IV programmers.
Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.
MC Press books written by Robert Cozzi available now on the MC Press Bookstore.
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