Oracle Architectural Components
Oracle Server:-\
* It contains Several files,process and memory strutures in an oracle server .Not all of them are used when executing a sql statment.
*The database can be recovered in event of software or hardware error.
*It consists of Oracle Instance and Database.
- Client-application server-server
- client-server
- host-based
Client-application-server:-\ (three tiers) user access the database from local computer through an application server.
Client-Server:-\ (two tiers) User access the database from their personal computer(client) over a network.Database sits in a separate computer(server).
Host-Based :-\ Users directly connected to the same computer on which the database resides.
Oracle Instance:-\
* It combination of Background process and memory struture.
*Instance must be started to access the data in database.
*when instance start----> SGA(system global Area ) allocated & bg process are started.
*It perform functions on behalf of invoking processes.
*Always open one and only database.
Oracle Database :-\
*It consists of Operating system files and also known as datafiles.
*It provide actual storage information and data kept consistent and can be recovered in event of
software or hardware error.
* It consists of three files,
Datafiles--Actual data in a database.
Redo logs --- A record changes of made to the database to enable recovery of the data in case of failures.
Control files ---- containg information necessary to maintain and verify database integrity.
Other Key Files :-
Password file
Parameter file (characterstics of an Oracle instance.it contains size of the sga and so) and Archived redo log file (Offline copies of the redo log files).
Establishing a connection & Creating Session:-
Database user(user process)<------connection established----->server process<---->(session create) oracle server.
* Before users can submit Sql statments to an oracle database,they must connect to an instance.
* Such as sql*plus (tool) or Oracle Forms(Application) is excuted as s user process.
* When user logs on to the Oracle server, A process is created on the computer running the Oracle Server. This process is called a Server process.
Sessions:-
* The session starts when the user is validated by the oracle Server and it ends when the user logs out or when there is an abnormal condition.
Example: When you log on to any mail id,it created session and then if you are not using particular time ,the session will be ended and then you again login.
* One to one correspondance between a user and server process is called a dedicated server.
* Possible for multiple user processes to share server processes.
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