  This note is dedicated to the study of the asymptotic behaviour of sets of
finite perimeter over RCD(K,N) metric measure spaces. Our main result asserts
existence of a Euclidean tangent half-space almost everywhere with respect to
the perimeter measure and it can be improved to an existence and uniqueness
statement when the ambient is non collapsed. As an intermediate tool, we
provide a complete characterization of the class of RCD(0,N) spaces for which
there exists a nontrivial function satisfying the equality in the
1-Bakry-\'Emery inequality. This result is of independent interest and it is
new, up to our knowledge, even in the smooth framework.
