Oracle Architecture

Oracle Architecture includes
1) Physical Structures
which can be seen physically with the eyes.

a) Data files
This files stores the data of all logical objects like tables, indexes etc.

b) Control files
This file stores the control information of all files in the database.

c) Redo log files
This files records all the changes done to the database.

d) Archive redo log files
The redo files archived are known as archive redo log files.


2) Memory Structures
This include two areas a) SGA b) PGA.

a) System Global Area (SGA).
SGA is Shared Memory Structures which is created at instance startup.
This mainly consists of Shared Pool Area, Redo Log Buffer , Database Buffer Cache, Large Pool, Java Pool
and Streams Pool (oracle 10g).

b) Program Global Area (PGA).
PGA is memory allocated outside the oracle instance.
This manily consists of Private SQL Area, Session Memory and SQL Work Area.

3) Processes

a) Server Process
Establish the connection to an oracle instance when a user process requests connection makes the connection for user process.

b) Background Process
Process running behind the scene are used to perform IO activities or to deal with abnormal conditions arising in the lifetime of the instance. Mandatory background process are SMON, PMON, LGWR, DBWR, CKPT, and RECO.

4) Logical Structures.
Table spaces and Schemas Objects.