Oracle and its process

INTRODUCTION:

Oracle is an RDBMS software provided by oracle development software cor poration .The RDBMS software supports the user declarative statements which describe the rules that the data must satisfy. Thus, an RDBMS provides all the users a facility to store & retrieve data in a consistent manner with a defined model called, RELATIONAL MODEL

ORACLE is also known as ORDBMS (OBJECT RELATIONAL DATABASE MANAGEMENT SYSTEM) which offers both relational & object oriented data base systems. Hence, Objects can be defined as REUSABLE SOFTWARE CODE, which are location independent and perform a specific task on any application environment with a little changes or no change at all, to the code.

Oracle products are based on client / server architecture technology. It involves segregating the process of an application between the systems. The server performs all the activities related to the database. The activities that help the user to interact with the application called CLIENT. The clients request the information to the Server (Backend Process) and Server responds to the Clients (Front end) after process.

S.G.A (SYSTEM GLOBAL AREA)

When oracle is loaded from a oracle server, certain background process & memory area is required for the oracle to run is allocated. The main memory area (or) virtual memory that will be allocated by the system is called S.G.A The combination of SGA and background processes together is an oracle database administrator. When the database is running, the SGA is the centre of oracle activity. It provides a communication between the user & back ground processes.

The SGA is having three CACHES , i.e., means of a storage area.

1.   STORED POOL

2.   REDO BUFFER

3.   DATABASE BUFFER

Thus, oracle processes are divided into 3 types, as,

1.   SERVER PROCESS     

2.   USER PROCESS   

3.   BACKGROUND PROCESS 

SERVER PROCESS:

The server process communicates with users to perform tasks on behalf of the user such as executing SQL commands/statements and returning the data to the user.

USER PROCESS:

The user process runs on a special machine called the client & server process runs on a server. Every client or user has a corresponding dedicated server process running on its behalf.

The user process is created whenever an application, or oracle tools connects to the database.

BACKGROUND PROCESS:

The back ground process perform the tasks related to the database. 

The four important process are,

a)   DATABASE WRITER

b)   LOG WRITER

c) PROCESS MONITOR            

d) SYSTEM MONITOR

DATABASE WRITER (DBWR):

The database writer is responsible for writing data in the database buffer to the secondary storage. Database buffers are the storage locations in SGA.

LOG WRITER (LGWR):

The log writer writes the data in the redo buffer to the redo mode files in the disk. They are used to recover the database,  in case of a database crash.

Process monitor (PMON) :

The process monitor is responsible for managing the user processes connected to the database.

System monitor (SMON):

The system monitor is responsible for managing the user for various processes associated with the database.

Further, the relational database model has classified into three components

1. Structural component is to build the data model

a.   Relational Objects (Tables)

b.   Attributes (also known as, columns)

c.   Rows (tuples).

    2.Integrity components which is the component to manipulate the

structure.

3. Integrity components which define the operational rules on the data.  

Thus, the general function provided by the DBMS is shielding of the database users from hardware level details. In other words, the DBMS provides users with a perception of the database i.e., elevated some what about the hardware level and it supports user option.