Oracle 9i Tutorials

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Oracle 9i Tutorial

1. What is Oracle? What are the primary compotnents of Oracle Architecture Database.
Oracle is a database which is developed by a company called Oracle Corporation Ltd.
Primary Components of Oracle architecture.
Oracle Server
A Database management system that provides an open, comprehensive and integrated approach to information management. There are several files, processes and memory structures in Oracle server. Some are used for SQL processing, some are for performance and some to ensure the recovery of database incase of error. It consists of Oracle Instance and an Oracle Database.
Oracle Instance: A combination of memory structure and background processes. Instance must be started to access the oracle database. When it starts SGA (System Global Area or called Shared Global Area is allocated and oracle background processes are also stared. Background processes perform input/output and monitor other oracle processes for better performance and reliability. It always open one and only one database at a time.

Oracle Database: Is a collection of data which consist of three types of files. Datafiles, Control files, redo log files.

Other Key files: Non database files such as password file, parameter file, archived redo log files are used to authenticate privileged users to start up and shut dow, to configure the instance and for recovery from media failures respectively.

User and Server Processes and Ohter Processes like Advance queuing, Real Application Clusters, Shared Server, Advance Replication.

2. How to eastablish connection to oracle server? What are different ways to connect to an Oracle server?
When user starts a tool such as SQL plus or runs any application user process is executed. When user logs on to Oracle server a process is created on the server. This process is called server process. Now this server process will communicated with oracle instance on behalf of the user process that runs on client.
In short, server process runs sql statements on behalf of user.
Connections:
There are three ways to establish a connetion with oracle server.

• User can log on to the OS on which oracle Instance is running and starts and application or tool which access the database on the same system. Interprocess communication is used to establish a communication pathway between oracle server and Host operating system.
• User starts an application or sql tool on one machine(client machine) and connects over a network to a machine running oracle instance. This configuation is also called Client-Server.
• Three Tiered Connection. Here user's computer communicates over Network to an application or N/w server which is connected to a network to the machine running the oracle instance.
  

3. What is a Session? When it starts and when it terminates?
Session is a specific connection of a user to an oracle server. It starts when user is validated by oracle server and teminates when user logs out or when there is an abnormal termination occures.

4. What is Memory Structure in Oracle?
Oracle consists of Two memory structures

• SGA ( System Global Area )
• Allocated when Oracle Instance starts. Fundamental Component of an Oracle Instace.
  
• PGA ( Program Global Area )
• Memory reserved for each user process connecting to Oracle database
• Allocated when a process is created.
• Deallocated when a process is terminated.
• Used by only one process.
  

5. Oracle Instance

Memory Structures

Shared Pool
Database Buffer Cache
Redo log buffer Cache
Large Pool
Java Pool

Backgroung Process Stuctures

PMON
SMON
DBWR
LGWR
CKPT

// Under Construction