An outage is any disruption in the ability of the database solution to serve user applications. Outages can be classified in two groups: unplanned outages and planned outages.
- The failure of one component of the system, including hardware or software failure.
- Invalid administrative or user application actions such accidentally dropping a table that is needed for business-critical transactions.
- Poor performance due to suboptimal configuration, or inadequate hardware or software.
- Maintenance. Some maintenance activities require you to take a complete outage; other maintenance activities can be performed without stopping the database, but can adversely affect performance. The latter is the most common type of planned outage.
- Upgrade. Upgrading your software or hardware can sometimes require a partial or a full outage.
In discussions about availability, the focus is often on disaster scenarios or component failures. However, to design a robust high availability solution, you need to address all of these types of outage.