Performance notes (SAP#34)

* Performance notes

* Performance notes

clean-abap/CleanABAP.md

@@ -551,6 +551,22 @@ Try to build things in a clean, object-oriented way.
 If something is too slow, make a performance measurement.
 Only then should you take a fact-based decision to discard selected rules.
 
+Some further thoughts, taken in part from Chapter 2 of 
+[Martin Fowler's _Refactoring_](https://martinfowler.com/books/refactoring.html):
+
+In a typical application the majority of the runtime is spent in a very small proportion 
+of the code. As little as 10% of the code can account for 90% of the runtime, and especially 
+in ABAP a large proportion of runtime is likely to be database time. 
+
+Thus it is not the best use of resources to spend significant effort on trying to make _all_ 
+code super-efficient all the time. We're not suggesting ignoring performance, but rather 
+focus more on clean and well structured code during initial development, and use the 
+profiler to identify critical areas to optimize. 
+
+In fact, we would argue that such an approach will have a net positive effect on performance 
+because it is a more targeted optimization effort, and it should be easier 
+to identify performance bottlenecks and easier to refactor and tune well structured code.
+
 ### Prefer object orientation to procedural programming
 
 > [Clean ABAP](#clean-abap) > [Content](#content) > [Language](#language) > [This section](#prefer-object-orientation-to-procedural-programming)