With link-state, one interface flap can mean doing SPF on every route.
Only if you learned every one of your routes from different neighbor. If you have two exits and 100000 routes, you calculate twice and apply the results to the prefixes.
Note that this does not apply to a proprietary, "hybrid", semi-link state protocol marketed with name "EIGRP" where all routes need per-prefix calculation. (OSPF and IS-IS work fine)
but.. with SPF you need to run the algorithm on all paths for each flap and then see what that does to your routes
with eigrp you only need to apply the algorithm to any route on the link that flapped and then only on the attached router (which will propogate much like bgp if it requires other routers to recalculate)
yes thats bad if yuo have 100000 routes but you shouldnt have! assuming a smaller routing table yuo get quicker convergence and much much less CPU requirement on your rotuers
And with nailed BGP routes you dont need additional layer of complexity. Alex