When we write a piece of data to a database, it is our hope that that data is immediately available to any other process that may wish to read it. From another point of view, when we read some data from a database, we would like to be guaranteed that the data we retrieve is the most recently updated version. This guarantee is called immediate consistency, and it's a property of most common single-master databases such as MySQL and PostgreSQL.
Distributed systems such as Cassandra typically do not provide an immediate consistency guarantee. Instead, developers must be willing to accept eventual consistency, which means when data is updated, the system will reflect that update at some point in the future. Developers are ...
