In many scenarios, however, eventual consistency is unacceptable. alice may be using the MyStatus web interface to update her e-mail address. After submitting the form with her updated information, the alice browser is redirected to a page where she can view her profile. At this point, the web application will need to read the profile data from Cassandra; if it happens to read from an out-of-data replica, it will appear to alice that her e-mail address was not actually updated.
At the other end of the consistency spectrum from ONE lies the ALL consistency level. At this level, all interested replicas must respond successfully in order for the request to be considered a success. If we update alice's e-mail address ...
