I have a stored procedure that I am calling using EXECUTE IMMEDIATE. The issue that I am facing is that the explain plan is different when I call the procedure directly vs when I use EXECUTE IMMEDIATE to call the procedure. This is causing the execution time to increase 5x. The main difference between the plans is that when I use execute immediate the optimizer isn't unnesting the subquery (I'm using a NOT EXISTS condition). We are using Rule Based Optimizer here at work.

Example: Fast:

begin
   package.procedure;
end;
/

Slow:

begin
   execute immediate 'begin package.' || proc_name || '; end;';
end;
/