As each site stores a complete replica of the database, each site can continue to work independently of the rest of the organisation as it can still find data from its own replica. However, it does mean that any updates to the database can be problematic as the updates cannot be distributed to the other replicas whilst the link is broken. Even when the communication links are available, the data may not be up to date. Updates to data may be carried out every few hours or every few minutes. A balance has to be found between the importance of having up to date data and reducing the amount of traffic across communication links. Therefore, a replicated database is not suitable for real-time systems such as flight booking systems where data must always be up to date. However, it is very suitable to a system where immediate updates are not crucial, for example in supermarket stock control systems.