Basic Oracle Physical Architecture

Oracle Server Architecture

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

Oracle Primary Architecture Component         

Oracle Terms:

Oracle Server – It is a combination of Oracle Instance and Oracle Database.

Oracle Database - Oracle database consists of file: datafiles, control files, redo log files and archive redo log files.  The Oracle server also accesses parameter files and password files.

Oracle Instance - Oracle Instance consists of two different sets of components:

1. Background processes - (PMON, SMON, RECO, DBW0, LGWR, CKPT, D000 and others).
2. Memory structures -   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. 

User and server processes – Manage the execution of Sql statements.

• Shared Server Process can share memory and variable processing for multiple user processes.
• Dedicated Server Process manages memory and variables for a single user process.

User - A User is the account you use to connect to a database.

Schema - A Schema is the set of objects (tables, views, etc.) that belong to that User account.

Tablespace - A tablespace is a storage location where the actual data underlying database objects can be kept.

                                         Oracle Database Physical structure 

Oracle Database consists of 3 types of physical files

1. Datafiles – These files contain the actual data.
2. Redo logfile - Store all changes made to the database as they occur and enable recovery when failures occur.
3. Control Files - A small binary file that records the physical structure of the database that includes – database name, locations of associated datafiles and redo files, checkpoint information, current sequence number etc.

Other key files as noted above include: 

1. Parameter file – there are two types of parameter files.
2. The init.ora file (also called the PFILE) is a static parameter file.  It contains parameters that specify how the database instance is to start up.
3.  The spfile.ora is a dynamic parameter file.  It also stores parameters to specify how to startup a database; however, its parameters can be modified while the database is running.
4.  Password file– specifies which *special* users are authenticated to startup/shut down an Oracle Instance.
5.  Archived redo log files – are copies of the redo log files and are necessary for recovery in an online, transaction-processing environment in the event of a disk failure.

 Memory Structures

The memory structures include three areas of memory:

1. System Global Area (SGA) – this is allocated when an Oracle Instance starts up.
2. Program Global Area (PGA) – this is allocated when a Server Process starts up.
3. User Global Area (UGA) – this is allocated when a user connects to create a session.

Note: A session is a connection of a user to an instance through a user process.

  Processes

Different types of Processes:

1.  User Process:  Starts when a database user requests to connect to an Oracle Server.
2. Server Process:  Establishes the Connection to an Oracle Instance when a User Process requests connection – makes the connection for the User Process.
3. Background Processes:  These start when an Oracle Instance is started up.

END OF NOTES 

click here : Detailed Physical Architecture

Follow : http://ithelpdeskinc.com/