Oracle - Components of the Oracle architecture

December 2016

[Oracle] Components of the Oracle architecture




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.

Oracle Instance


The Oracle instance allows you to access the Oracle database ( opening only one database).
The Oracle instance consists of:
  • Background process : 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:
  • Memory area allocated to the SGA (System Global Area) : 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
  • 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.

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.

Oracle database


The Oracle database is a collection of data treated as a single entity and consists of three types of files including:
  • Control files
  • Data Files
  • Log files

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