Oracle9i Database Administration Fundamentals I 1-2
Overview of Primary Components
The Oracle architecture includes a number of primary components, which
are discussed further in this lesson.
• Oracle server: There are several files, processes, and memory structures
in an Oracle server; however, not all of them are used when processing a
SQL statement. Some are used to improve the performance of the
database, to ensure that the database can be recovered in the event of a
software or hardware error, or to perform other tasks necessary to
maintain the database. The Oracle server consists of an Oracle instance
and an Oracle database.
• Oracle instance: An Oracle instance is the combination of the
background processes and memory structures. The instance must be
started to access the data in the database. Every time an instance is
started, a System Global Area (SGA) is allocated and Oracle background
processes are started. Background processes perform functions on
behalf of the invoking process. They consolidate functions that would
otherwise be handled by multiple Oracle programs running for each user.
The background processes perform input/output (I/O) and monitor other
Oracle processes to provide increased parallelism for better performance
and reliability.