Oracle Database architecture

1. Oracle Database
Architecture

2. Overview
An Oracle database consists of an
instance and its associated
databases.
The instance consists of memory
structures and background
processes.

3. Connecting to the Database
 A connection is a communication pathway betweenauser processand an Oracle
Database instance.
 A session represents the state of a current user logintothedatabaseinstance.

4. Interacting with an Oracle Database
1. An instance has started on a node where Oracle Database is installed, often
called the host or database server.
2. A user starts an application spawning a user process .The application attempts to
establish a connection to the server.
3. The server runs a listener that has the appropriate Oracle Net Services handler.

5. Oracle
Database Server Structures
An Oracle instance uses memory
structures and processes to
manage and access the database.

6. Oracle Database Memory Structures
Two basic memory structures are associated with an instance:
System Global Area (SGA)
Program Global Areas (PGA)

7. Database Buffer Cache
The database buffer cache is the portion of the SGA that holds copies of data blocks
that are read from datafiles.

8. Redo Log Buffer
The redo log buffer is a circular buffer in the SGA that holds information about changes
made to the database. This information is stored in redo entries.

9. Shared Pool
The shared pool portion of the SGA contains the library cache, the data dictionary
cache, the SQL query result cache, the PL/SQL function result cache, buffers for
parallel execution messages, and control structures.

10. Process Architecture
User processes
Server Processes
Background Processes

11. background processes
Database writer process (DBWn)
Log writer process (LGWR)
Checkpoint process (CKPT)
System Monitor process (SMON)
Process monitor process (PMON)
Recoverer process (RECO)
Job queue processes Archiver
processes (ARCn)
Queue monitor processes (QMNn)

12. Database Writer Process(DBWn)

13. Log Writer Process(LGWR)

14. Checkpoint Process(CKPT)

15. System Monitor Process(SMON)

16. Process Monitor Process(PMON)

17. Archiver Processes (ARCn)

18. Server Process and Database Buffer Cache

19. Oracle Storage Structure

20. Thanks!