COBOL Performance Tuning - Using Conditional Statements

This performance tuning tip is one that can be applied to any language that you program in.

When you evaluate a field for more than one possible value, whether you use an IF, EVALUATE, GO TO DEPENDING ON, or some other conditional statement, check for the most common value first, then the next common, and so on.

For example, if you are reading through a file and you only want records that are in "A" Active, "W" Waiting or "P" Pending status, and you know out of the one million records you will be reading that about 900,000 of them are active, 30,000 are waiting, 20,000 are pending and the rest are something else, you will want to something like the following:

IF MY-STATUS = "A"

    PERFORM STATUS-IS-A THRU STATUS-IS-A-EXIT

    GO TO PARA-EXIT

ELSE

    IF MY-STATUS NOT EQUAL "W"AND

         MY-STATUS NOT EQUAL "P"

            GO TO PARA-EXIT

    ELSE

        IF MY-STATUS = "W"

            PERFORM STATUS-IS-W THRU STATUS-IS-W-EXIT

        ELSE

            PERFORM STATUS-IS-P THRU STATUS-IS-P-EXIT

        END-IF

        GO TO PARA-EXIT

    END-IF

    GO TO PARA-EXIT

END-IF.

I don't know how many programmers think about this scenario when they code, but I suspect many do not.