After completing this lesson, you should be able to do
• Create and manage initialization parameter files
• Start up and shut down an instance
• Monitor and use diagnostic files.
Initialization Parameter Files
• Entries are specific to the instance being started
• Two types of parameters:
– Explicit: Having an entry in the file
Initialization Parameter Files
In order to start an instance and open the database, you must connect as SYSDBA and enter the STARTUP command. The Oracle server will then read the initialization parameter file and prepare the instance according to the initialization parameters contained within.
Note: You must have SYSDBA privilege. Authentication and the SYSDBA privilege will be discussed in later lessons.
The Oracle server is an object-relational database management system . It provides an open,
comprehensive, and integrated approach to information management. An Oracle server is combination
of an Oracle database and an Oracle server instance.
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.
The Oracle server uses many memory components, background processes, and file structures for its backup and recovery mechanism. This lesson reviews the concepts presented in the Oracle9i Database Administration Fundamentals I course, with an emphasis on backup and recovery requirements.
An Oracle instance consists of memory areas (mainly System Global Area [SGA]) and background processes, namely PMON, SMON, DBWn, LGWR, and CKPT. An instance is created during the nomount stage of the database startup after the parameter file has been read.
After completing this appendix, you should be able
to do the following:
Describe the Oracle Server architecture and its main components
List the structures involved in connecting a user to an Oracle instance
List the stages in processing:
The Oracle Database (commonly referred to as Oracle RDBMS or simply as Oracle) is an object-relational database management system produced and marketed by Oracle Corporation.An Oracle database system—identified by an alphanumeric system identifier or SID—comprises at least one instance of the application, along with data storage. An instance—identified persistently by an instantiation number
Oracle Database Performance Tuning Guide is an aid for people responsible for the
operation, maintenance, and performance of Oracle. This book describes detailed
ways to enhance Oracle performance by writing and tuning SQL properly, using
performance tools, and optimizing instance performance. It also explains how to
create an initial database for good performance and includes performance-related
reference information. This book could be useful for database administrators,
application designers, and programmers.
Oracle Server Configuration Options
Oracle creates server processes to handle the requests of user processes connected to an instance. A server process can be either a dedicated server process, where one server process services only one user process, or it can be a shared server process, where a server process can service multiple user processes. Shared server processes are a part of Oracle Shared Server architecture.
Before a database is created, the UNIX environment must be configured and the Oracle9i server must have already been installed.
Four environment variables must be set: ORACLE_HOME, ORACLE_SID, PATH, LD_LIBRARY_PATH.
ORACLE_HOME is the full path to the top directory in which the Oracle9i Server is installed. The directory for ORACLE_HOME should be supplied by the person who installed the server, usually the UNIX administrator or the DBA.
ORACLE_SID is a user-definable name assigned to an instance of a database.
Using Online Redo Log Files
Online redo log files provide the means to redo transactions in the event of a database failure. Every transaction is written synchronously to the Redo Log Buffer, then gets flushed to the online redo log files in order to provide a recovery mechanism in case of media failure. (With exceptions such as direct load inserts in objects with the NOLOGGING clause enabled.) This includes transactions that have not yet been committed, undo segment information, and schema and object management statements.
When additional resources are required, additional nodes and instances can easily
be added to the cluster with no downtime. Once a new instance has been started,
applications using services can immediately take advantage of it with no changes to
the application or application server.
Oracle Real Application Clusters is an extension to the Oracle Database and
therefore benefits from the manageability, reliability, and security features built into
the Oracle Database.