Solving a route using the exact route solver, and the Hierarchy option in ArcMap is not checked, takes a long time to compute or runs out of memory.
The route being solved is a long route that spans across a large network. For example, the network has local road detail for an entire continent, and the route travels from one end of the continent to the other.
The exact route solver implementation is based on the Dijkstra algorithm. It grows the shortest path tree until the destination is reached.
This search technique, which guarantees optimality, may require exploring the entire network. The application may run out of memory in attempting to keep the entire network in memory. Even if the memory does not run out, the route may take a long time to compute, since the application will need to manage large amounts of memory.
This option may not return the optimal route.