Oracle Background Process

To maximize the performance and accommodate many users, a multiprocessing oracle system use some additional database process called background process.
The relationship between the physical and memory structures is maintained and enforced by Oracle’s background processes.

Mandatory background process :

• System monitor (SMON)
• Process monitor (PMON)
• Database writer (DBWR)
• Log writer (LGWR)
• Checkpoint (CKPT)

Optional process:

• Archival  (ARCn)

What is Oracle Database

Oracle database is a collection of data treated as a unit. The purpose of a database is to store and retrieve related information.
A database server is the key to solving the problems of information management which can be to efficiently retrieved, updated and analyzed and authenticated .
A database is a collection of information that is organized so that it can be easily accessed, managed and updated.
Oracle Database Architecture consists of following three main structures:

• Storage Structure
• Memory Structure
• Process Structure

When a database is created, database files are created. These files include Control files, Data files, online redo log files, parameter file and password file. All these files
formulate “Storage Structure”.

When oracle Database is started on Database Server, oracle software allocates shared memory area and also starts several processes to run database. The shared memory area is called System Global Area (SGA).The combination of System Global Area and background Processes is known as Oracle Instance. Oracle Instance formulates Memory Structure and Process Structure.Each instance in oracle server is associated with a specific database. The process of assigning an instance to a database is called Mounting. After mounting, database is opened and becomes accessible for users. Multiple instances can run on single computer.

In RAC (Real Application Cluster)  more than one  instance point to single database.

                                  Instance=SGA + Background process

Resolving TNS – Message 3511 not found

C:\Users\Administrator.ANURAG-PC>tnsping ducat

TNS Ping Utility for 32-bit Windows: Version 11.2.0.1.0 - Production on 27-DEC-2017 21:46:23

Copyright (c) 1997, 2010, Oracle.  All rights reserved.

Message 3511 not found; No message file for product=NETWORK, facility=TNSTNS-03505: Message 3505 not found; No message file for product=NETWORK, facility=TNS

C:\Users\Administrator.ANURAG-PC>set ORACLE_BASE=D:\app\ANURAG

C:\Users\Administrator.ANURAG-PC>tnsping ducat

TNS Ping Utility for 32-bit Windows: Version 11.2.0.1.0 - Production on 27-DEC-2017 21:53:16

Copyright (c) 1997, 2010, Oracle.  All rights reserved.

Message 3511 not found; No message file for product=NETWORK, facility=TNSTNS-03505: Message 3505 not found; No message file for product=NETWORK, facility=TNS

C:\Users\Administrator.ANURAG-PC>set ORACLE_HOME=D:\app\ANURAG\product\11.2.0\client_1

C:\Users\Administrator.ANURAG-PC>
C:\Users\Administrator.ANURAG-PC>


Solution
=============

C:\Users\Administrator.ANURAG-PC>set ORACLE_BASE=D:\app\ANURAG

C:\Users\Administrator.ANURAG-PC>tnsping ducat

TNS Ping Utility for 32-bit Windows: Version 11.2.0.1.0 - Production on 27-DEC-2017 21:53:16

Copyright (c) 1997, 2010, Oracle.  All rights reserved.

Message 3511 not found; No message file for product=NETWORK, facility=TNSTNS-03505: Message 3505 not found; No message file for product=NETWORK, facility=TNS

C:\Users\Administrator.ANURAG-PC>set ORACLE_HOME=D:\app\ANURAG\product\11.2.0\client_1

C:\Users\Administrator.ANURAG-PC>
C:\Users\Administrator.ANURAG-PC>
C:\Users\Administrator.ANURAG-PC>tnsping ducat

TNS Ping Utility for 32-bit Windows: Version 11.2.0.1.0 - Production on 27-DEC-2017 21:53:44

Copyright (c) 1997, 2010, Oracle.  All rights reserved.

Used parameter files:
D:\app\ANURAG\product\11.2.0\client_1\network\admin\sqlnet.ora


Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.48)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = ducat)))
OK (0 msec)

C:\Users\Administrator.ANURAG-PC>

Connecting to an Oracle Instance

Connecting to an Oracle Instance

Before users can submit SQL statements to an Oracle database, they must connect to an instance.

• The user starts a tool such as SQL*Plus,sql developer,toad or runs an application developed using a tool such as Oracle Forms. This application or tool is executed as a user process.

• In the most basic configuration, when a 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. The server process communicates with the Oracle instance on behalf of the user process that runs on the client. The server process executes SQL statements on behalf of the user.

User Process is started at the time a database user request  a connection to the oracle server .

Server Process connect to the oracle instance and started when a user establish a session .

user process & server process are used to manage the execution of sql/plsql statements .

one-to-one correspondence between the User and Server Processes. This is called a Dedicated Server connection. An alternative configuration is to use a Shared Server where more than one User Process shares a Server Process.

Server Process is the go-between for a Client Process and the Oracle Instance.

Dedicated Server environment – there is a single Server Process to serve each Client Process.

Shared Server environment – a Server Process can serve several User Processes, although with some performance reduction

Connection

A connection is a communication pathway between a user process and an Oracle server. A database user can connect to an Oracle server using tool, sqlplus etc.

Sessions

A session is a specific connection of a user to an Oracle server. 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 termination. For a given database user, many concurrent sessions are possible if the user logs on from many tools, applications, or terminals at the same time.