qgis - Update values from layer one to layer two where there is no identical ID but identical geometry

I have one huge problem and that is to get the value from one layer into another. It is a network with over a million links and I need to update a table from a layer of + 100 000 links. I am using QGIS and tried intersect, overlap on smaller data but I don't get the result I want. The two layers have identical geometry but one layer for example can have one long link compare to layer two that can have several links (road intersections) so overlap and intersection does not work. I did try the "Select by location" and "Include input features completely within the selection features" It did work as I wanted but when trying on the bigger data it just sit there for many hours (or overnight) and I don't know if it is working or just freezed in the process. All I want is to match the data and update the values from one layer to the other. As there is no identical ID I can not use the "Join" function but have to use geometry match instead. Is there another way around this problem?