Replication

Replication is defined as:

"The process of generating and reproducing multiple copies of data at one or more sites."
- Thomas M Connolly, Carolyn E Begg, 2002.

When a database instance fails, the service it provided must be available through another route. This requires process redundancy. In a database, either only one processor can process all transactions, or there can be multiple processors. When there is a single process managing all transactions, we should have a standby process available, in the case of failure, for an active one. It is also necessary to make sure that this fail-over is seamless and the process itself can detect the failure.

Data redundancy is also required for high availability. Data redundancy...