Components of SGA

COMPONENTS OF SGA

 

Components of SGA :

 Mandatory Components :

  1.DBBC(Database Buffer cache)

  2.Shared Pool

    a.Library Cache

    b.Data Dictionary cache

  3.Redolog buffer

 Optional Components :

  

   1.Large pool

   2.Java pool

   3.Streams pool

 Components of Background Process

  Mandatory Components 

   1.DB WRITER (DBWR)

   2.LOG WRITER (LGWR)

   3.CHECK POOL PROCESS (CKPP)

   4.SYSTEM MONITOR (SMON)

   5.PROCESS MONITOR (PMON)

   6.RECOVER PROCESS (RECO)

  Optional Components

   1.ARCHIVER (ARCH)

   2.MEMEORY MANAGER

   3.DISPATCH PROCESS

   4.CLOCK MONITOR

   5.JAK QUEE (CJQ)

 

Infomation table of datafiles

Brief notes on Database files

  Database files :

 There are 3 different database files

   1.Control Datafile
   2.Redolog Datafile
   3.Datafile

1. Control file:

   ->It controls the database
   ->the most important file in an oracle database
   ->it is small binary file necessary for DB to open or start database successfully.
   ->Every Oracle DB must have alteast 1 control file.

   The control file contains :

   1.It contains name of the database
   2.Time Stamp of database creation
   3.It contains all the files of database
   4.It Contains name and locations of datafiles and redolog.
   5.Archived log Information
   6.log sequence no (LSN)
   7.check point Information
   8.System Change no
   9.Backup set details


2.Redolog File:

  ->It Contains latest Transaction
  ->It contains all the modification or Updations
  ->This file is very important file during the recovery database.
  ->All committed  data goes redolog file
  ->In database we must create 2 redolog groups , in each group it should have alteast 1 redolog file


3 Datafile :

To create a database there will be 3 datafiles
     a.System datafile
     b.Sysaux datafile
     c.Undo datafile

a.System datafile :

  ->It is introduced in oracle version 9C
  ->It contains the metadata (Structure of database) stored in system file in the form base tables.
 

 b.Sysaux Datafile :

   ->It acts as secondary system file to reduce the performance related tables

         AWB (Automatic workload repository)
         ADDM (Automatic DB Diagnostic Moniter)

   ->To reduce the work load of the system file


 c.Undo Datafile :

   ->It contains the previous image of the transaction

Optional Database file :

 1.User datafile :it contains the user related Information .

 2.User index : It contains indexes information created by user.

 3.Temporary datafile : It contains temporary data for sorting purpose.

Database Arcitecture

Database Arcitecture

Database architecture is divided in to 2

   1.Database instance
   2.Database


1.Database Instance :

-->Database Instance Structure. When an instance is started, Oracle Database allocates a memory area
called the system global area (SGA) and starts one or more background processes. The SGA serves various
purposes, including the following:

-->The combination of both SGA and background process is called the database instance .

2.Database:  

              It is classified into 2 layers
                a. logical layer
                b. Physical layer

a)Logical layer - (Tables,Views,Index,Synonyms , Sequences)
b)Physical layer - ( DBfiles --> Filesystem --> Operating system --> Disk)