Some systems may involve fewer components; for example, a two-tier
client/server system would not have the additional application server components.
Failures in the components above the database can effectively prevent access to the
database even though the database itself may be available. The database server and
the database itself serve as the foundation for the stack. When a database fails, it
immediately affects the higher levels of the stack. If the failure results in lost or corrupted
data, the overall integrity of the application may be affected.
The potential threats to availability span all of the components involved in an application
system, but in this chapter we??™ll examine only availability issues relating
specifically to the database.
System Failure
The abrupt failure of the server machine running the database is one of the most
common causes of unplanned downtime. A server may crash because of hardware
problems, such as the failure of a power supply, or because of software problems,
such as a process that begins to consume all the machine??™s CPU resources.
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