Databases Reference
In-Depth Information
Figure 11-2. Technology components in the system stack
As this figure shows, a variety of physical and logical layers must cooperate to deliver
an application. Failures in the components above the Oracle database can effectively
prevent access to the database even though the database itself may be available. The
server hardware, software, and database itself serve as the foundation for the stack.
When an Oracle 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.
Server Hardware, Storage, and Database Instance Failure
The failure of servers or storage hosting a database can be one of the most abrupt 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. Even if the underlying server platform is
fine, the Oracle instance itself can fail. Whatever the cause of the crash, the effect on
Oracle is the same—the instance cannot deliver its promised functionality. Remember
that when an Oracle Database crashes, it is the instance that crashes, not the database
