  We study stochastic processes in which the trajectories are constrained so
that the process realises a large deviation of the unconstrained process. In
particular we consider stochastic bridges and the question of inequivalence of
path ensembles between the microcanonical ensemble, in which the end points of
the trajectory are constrained, and the canonical or s ensemble in which a bias
or tilt is introduced into the process. We show how ensemble inequivalence can
be manifested by the phenomenon of temporal condensation in which the large
deviation is realised in a vanishing fraction of the duration (for long
durations). For diffusion processes we find that condensation happens whenever
the process is subject to a confining potential, such as for the
Ornstein-Uhlenbeck process, but not in the borderline case of dry friction in
which there is partial ensemble equivalence. We also discuss continuous-space,
discrete-time random walks for which in the case of a heavy tailed step-size
distribution it is known that the large deviation may be achieved in a single
step of the walk. Finally we consider possible effects of several constraints
on the process and in particular give an alternative explanation of the
interaction-driven condensation in terms of constrained Brownian excursions.
