Distributed Database Patterns
Administrators of web applications have traditionally had two choices when the application demand exceeds database capacity: scaling up by increasing the power of individual servers, or scaling out by adding more servers. For most of the relational database era, scaling up was the more practical option. Early relational databases did not provide a clustering option, whereas the CPU and memory supplied by a single server was constantly and exponentially increasing in line with Moore’s law. Consequently, scaling out was neither practical nor necessary.