Column Gerneration Example in the documentation/hot start after adding variables to LP

Hi all,
I just started using Julia and JuMP. I went through the tutorials
(Cutting stock · JuMP) and in the column generation example and in general it is unclear to me if the problem gets re-solved from scratch whenever I add a new variable to the model or if the model “in the solver” is updated and there is a hot start from the current solution.
More general, if a JuMP model is changed after it was solved and I solve the changed version, is it solving from scratch or is there a hot start in the solver?
From the documentation I guess it’s only changing the model in the solver when using solver independent callbacks (Solver-independent Callbacks · JuMP).

Thanks a lot in advance!

It depends on the solver. In most cases, JuMP maintains the model in memory, so it doesn’t rebuild every time.