The architecture that Oracle has built its database around is designed to perform quickly, efficiently and without errors. Oracle Architectural Components describe the Oracle architecture and its main components as well as the structures involved in connecting a user to an Oracle instance. The Oracle server is the system that manages databases and provides comprehensive and integrated information management. An Oracle server consists of an instance and a database. The oracle architecture has following components:
Oracle Instance :
Database files themselves are useless without the memory structures and processes to interact with the database. Oracle defines the term instance as the memory structure and the background processes used to access data from a database. The Oracle instance allows to access the Oracle database.
Background process to manage and implement the relationships between physical structures and memory structures. There are two categories.
Mandatory background processes: DBWN, PMON, CKPT, LGWR, SMON.
Optional background process: ARCn, LMDn, RECO, CJQ0, LMON, Snnn, Dnnn, Pnnn, LCKn, QMNn .
Memory structures consisting of essentially of two memory areas.
1. Memory area allocated to the SGA (System Global Area) are allocated to start the instance and represents a fundamental component of an Oracle instance. It consists of several memory areas:
The shared memory area
The buffer cache of the database
Buffer logging and other structures for the management of internal and external locks, statistical data, etc …
The LARGE POOL memory area
The Java memory area
2. Memory allocated for the PGA (Program Global Area) is allocated at the start of the process server. It is reserved for each user process that connects to the Oracle database and is released at the end of the process.
The user process:
The program which interacts with the database by starting a connection. It communicates only with the process server. There are two categories of processes that run with an Oracle database.
The first interaction with the Oracle-based application comes from the user computer that creates a user process. The user process then communicates with the server process on the host computer.
Process Servers :
Represents the program that interact directly with the Oracle server. It responds to all requests and return results. It can be dedicated to a client or a server shared by many.
The Oracle database is a collection of data treated as a single entity and consists of three types of files including:
Control files are used to store information about physical structure of database. The control file is absolutely crucial to database operations.
Data Files :
A data file is a file that corresponds with a tablespace. A Tablespace is a grouping logical database objects. One data file can be used by one tablespace, but one tablespace can has more than one data files. An Oracle database include of a number of physical files called data file.
A Log is a file that is part of an Oracle Database. When a transaction is committed the transaction’s details in the redo log buffer is written in a redo log file. These files contain information that helps in recovery in the event of system failure.
An Oracle database consists of files. Sometimes these are referred to as operating system files, but they are actually database files that store the database information that a firm or organization needs in order to operate.