Indicates that a particular event is collective.
event - The event id
collective - Boolean flag indicating whether a particular event is collective
New events returned from
PetscLogEventRegister() are collective by default.
Collective events are handled specially if the -log_sync is used. In that case the logging saves information about two parts of the event; the time for all the MPI ranks to synchronize and then the time for the actual computation/communication to be performed. This option is useful to debug imbalance within the computations or communications