This model is a lazy-loaded model; its features are only loaded
into memory when they are first needed. The model uses some caching, but all caches
are soft-referenced. VPF feature objects are reused and should therefore not be referenced
(see the next section for more information on referencing objects).
The more memory is available, the better the model will perform (less cache misses).
This model also is a lazy-loaded model, closing the gap between the
in-memory and the on-the-fly model. It uses caches, of which the most frequently accessed ones
are permanently kept in memory, while the others are soft-referenced (resulting in a higher
minimum memory requirement than the on-the-fly model, but also a more consistent performance). The
more memory is available, the better the model will perform (less cache misses).