This book covers in-database replication only. Replication is also possible in the application layer (that is, above the database) or in the Operating System (OS) layers (that is, below the database):
- Application-level replication: For example, HA-JDBC and rubyrep
- OS-level replication: For example, DRBD
None of these approaches are very satisfying, since core database features cannot easily integrate with them in ways that truly work. From a sysadmin's perspective, they work,
but not very well from the perspective of a database architect.