Copyright © Oracle Corporation, 2002. All rights reserved.
Oracle Architectural Components
Oracle9i Database Administration Fundamentals I 1-2
Copyright © Oracle Corporation, 2002. All rights reserved.
1-2
Objectives
After completing this lesson, you should be able to do
the following:
• Outline the Oracle architecture and its main
components
• List the structures involved in connecting a user to
an Oracle instance
Objectives
This lesson introduces the Oracle server architecture by examining the physical, memory,
process, and logical structures involved in establishing a database connection, creating a
session, and executing SQL commands.
Oracle9i Database Administration Fundamentals I 1-3
Copyright © Oracle Corporation, 2002. All rights reserved.
1-3
Password
file
Overview of Primary Components
Instance
SGA
Redo Log
Buffer
Shared Pool
Data Dictionary
Cache
Library
Cache
DBWRSMONPMON CKPTLGWR Others
User
process
Server
process
PGA
Control
files
Data
files
Database
Database
Buffer Cache
Redo Log
files
Java Pool
Large Pool
Parameter
file
Archived
Log files
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.
Oracle9i Database Administration Fundamentals I 1-4
Overview of Primary Components (continued)
• Oracle database: An Oracle database consists of operating system files, also known as
database files, that provide the actual physical storage for database information. The
database files are used to ensure that the data is kept consistent and can be recovered in
the event of a failure of the instance.
• Other key files: Nondatabase files are used to configure the instance, authenticate
privileged users, and recover the database in the event of a disk failure.
• User and server processes: The user and server processes are the primary processes
involved when a SQL statement is executed; however, other processes may help the
server complete the processing of the SQL statement.
• Other processes: Many other processes exist that are used by other options, such as
Advanced Queuing, Real Application Clusters, Shared Server, Advanced Replication,
and so on. These processes are discussed within their respective courses.
Oracle9i Database Administration Fundamentals I 1-5
Copyright © Oracle Corporation, 2002. All rights reserved.
1-5
Oracle Server
An Oracle server:
• Is a database management
system that provides an open,
comprehensive, integrated
approach to information
management
• Consists of an Oracle
instance and an Oracle
database
Oracle server
Oracle Server
The Oracle server is the key to information management. In general, an Oracle server must
reliably manage a large amount of data in a multiuser environment so that many users can
concurrently access the same data. All this must be accomplished while delivering high
performance. An Oracle server must also prevent unauthorized access and provide
efficient solutions for failure recovery.
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