Not every day I see something like:
--- Generating MIP model xxxxx
I.e. GAMS generates a huge model (it is actually an LP – all integers are relaxed) that is reduced to almost nothing by the presolver in Cplex. Turns out there are many accounting rows in the model. Nowadays these are better formulated outside the model with assignment statements instead of using model equations.
GAMS actually generates this model quite quickly and efficiently. Opposed to what many people think, the larger the LP model, the better the relative performance of a modeling system. They often can create the model in (hopefully) linear time (linear in the number of nonzero elements), while even the best LP solvers don’t have this linear time behavior.