Virtuoso Space Based Router (VSR) Routing Methodology

My question is maybe not too relevant for this section (kind of off-topic) but I am very much interested in understanding how does VSR is very fast to route big layouts?. Typically a router is combination of shortest path algorithms and some design constraints. For shortest path between pins typically the algorithm has to traverse through the nodes of graph (coordinates of maze/grid) and based in the step size these nodes could be 100 Million to 1 Billion for bigger circuits. How does VSR can traverse through these nodes and solve the big circuits and reasonable time?. Is is because the grid/maze is hard coded in the virtuoso layout suits and all shortest paths are also saved ?.

I was trying to write my own router but for bigger layouts I realized my router has become much slower because of Millions of graph nodes. I am very much interested in understanding the engineering behind this router.

P.S: I hope I am not asking something which shouldn't be shared on public forum