Oracle PL/SQL Programming, 5th Edition

Native Compilation

In its default mode (interpreted), your code is partially compiled, but also interpreted at runtime. PL/SQL executes in a virtual machine, and it first translates (compiles) your code into virtual machine code, sometimes called bytecode or mcode. This is basically the same model that Java uses. When it is time to actually run your code, however, that bytecode is translated (interpreted) into system calls.

However, once you have the code running well, you can choose to improve the runtime efficiency of your PL/SQL programs by having the database perform the bytecode to machine code translation early, at compile time. This second half compilation (called native mode) results in machine code in a shared library. The database will dynamically load this compiled machine code at runtime.

When to Run Interpreted Mode

So, if native mode is faster, why run in interpreted mode? Let’s look at this question from the other end. The goal of native mode is fast execution speed. So, to get the fastest execution speed, you crank up the optimization level and try to do as much work ahead of execution time as possible (including early translation to machine code). When you are developing and unit testing your code, you need the capabilities of the debugger more than you need fast execution speed. If you need to step through your source code and step over subprogram calls in a debugger, you surely can’t have the optimizing compiler rearranging your source code (optimization level 2) ...