It depended on when the cathedral was consecrated, who was doing the consecration, and the association between the place and local saints. This is also complicated by the fact that most cathedrals had a number of altars within them, usually dedicated to popular or locally popular saints. You might read Patrick Geary's "Furta Sacra: Thefts of Relics in the Central Middle Ages," to get some idea of the formal and informal processes.