Disadvantages of Optimistic Approach
Thrashing behavior where most of the time is spent executing incorrect computations and rolling them back.
Periodically saving the state of each logical process can seriously degrade performance. The state-saving problem is further exacerbated by applications that requires dynamic memory allocation because one may have to traverse complex data structures to save the process's state.
In general, optimistic methods are much more complex to implement than conservative approaches.
Debugging is time consuming because it may require detailed analysis of complex rollback scenarios.