Oracle Architecture

Oracle Architecture-

oracle software works on basically few componet on  computer 

1- RAM-  oracle created memory components.

2- some background process or program.

3- Harddisc- permanent file like datafiles and password file and others

The architecture includes physical components, memory components, processes, and logical structures.

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 An Oracle server includes an Oracle Instance and an Oracle database.

Oracle instance: An Oracle Instance consists of tw o different sets of components:

The first component set is the set of background processes (PMON, SMON, RECO, DBW0,
LGWR, CKPT, D000 and others).

 Each background process is a computer program. These processes perform input/output and monitor other Oracle processes to providegood performance and database reliability.

The second component set includes the memory structures that comprise the Oracle instance. 

When an instance starts up, a memory structure called the System Global Area (SGA) is allocated. 

At this point the background processes also start. An Oracle Instance provides access to one and only one Oracle database.

Oracle database: 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.
· The redo log files are used to recover the database in the event of application program
failures, instance failures and other minor failures.
· The archived redo log files are used to recover the database if a disk fails.

Other files not shown in the figure include:

The required parameter file that is used to specify parameters for configuring an Oracle
instance when it starts up. 

The optional password file authenticates special users of the database – these are
termed privileged users and include database administrators.  

Alert and Trace Log Files – these files store information about errors and actions taken that affect the configuration of the database.

User and server processes:-

 These processes are used to manage the execution of SQL statements.

A Shared Server Process can share memory and variable processing for multiple user
processes.

A Dedicated Server Process manages memory and variables for a single user process .

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