ORACLE DATABASE ARCHITECTURE 

            what is architectur 

•  board outlines,mechanisms and design 

•  architecture is the combination of hardware and software which is completly relive one is depend on the other one 

main components of architecture with respect to oracle server 

                                 1) ORACLE DATABASE 

it is a completly base on the storage level component. which means combination of difrent types of file together comes on oracle database.its completly depending on storage its require a more and more spacess. 

                                 2)ORACLE INSTANCE 

 oracle instance is northing but a memory structure and baground process(in os level).its majorly relate on memory structure along with some baground process at operating system level.

              oracle database dividing in two types 

   1)physical structure

 An Oracle database is a set of files that store Oracle data in persistent disk storage its called physical structure 

  a)contol file 

controfiles are the file holding the control information about the database physical structure of the database store in the control files. its also maintain the consistency of the database.it is also called "heart of the databae".its also holds the information about database files. extension name is '.ctl' 

 

controlfile cantains 

 

* database name 

 * name,path,size of redq logfile

 * scn number 

 * archive log information

 * rman backup information

 * log sequential number

  b)redo logfile 

 redo log files are the file record changes make to database and its hold the current image,previous image in terms of redo groups.its an used recovery purpose. extension name is '.log' 

                             status of redolog

  cuurent: cuurent transaction taking place in that group

          active : this indicate content  can writen

        inactive : this indicate content  can no writen

        unused :  the group data is use not even ones

 c)data file

 its store a actual data and metadata.extension name is '.dbf' three types of datafile 

  !)system datafile:system related information

 !!)sysoux datafile:meta data information of table

 !!!)non system datafile:   

              

               * user datafile               * temporary datafile                * undo datafile 

 d)parameter file

parameter file hold the charactersticks of database and instance its used to startup of database and creation of database 

 two types of parameter file

!)parameter file:

its a text file we can change using ' vi ' command extension name is init sid.ora 

!!)server parameter file:

its also called a spfile. its a 'binary file'.we can change using alter command extension name is spfile sid.ora 

 e)password file its holds the sysdba,sysoper and difrent user passwords 

 f)archive logfile its an offline copy of online redo logfile 

 2)logical structure

    its physio logical structure in which data is store logicaly in physical structure 

a)tablespace 

            two types of tablespace 

        !) small file tablespace 

       !!)big file tablespace 

  

      based on space management 

 !)localy managed tablespace: space alocation delocation represent or managed in bitmap header 'non system tablespace managed localy'

 !!)Dictionary managed tablespace: space alocation delocation refered in data dictionary.'system and sysaux managed dictionary managed'

b)segment  segment is an part of tablespace it includes one or more extents

 c)extents  extens is part of segment it haves number of block space alocation and delocation will  always happen in terms of extents 

 d)blocks  it s smallest storege unit of oracle database,data will exactly stored here 

                             

                  SYTEM GLOBAL AREA 

 1)shared pool 

 !)library cache :most recently executed pl&sql and sql statement                              !!)dictionary cache :it holds the information related to the recently executed sql statement 

 !!!)large pool :it holds the information about backup and recovery 

 2)db cache :it holds the actual data inside of buffer 

 !)clean buffer: which has not using ones its called clean buffer 

 !!)pin buffer: which holds the black images which yet to modify its called pin buffer               !!!)dirty buffer:it is the modify buffer 

 !v)free buffer :buffer that can be over writen 

 3)redolog buffer cache: it holds the records changes made to the data in bufffer cache 

 PROGRAM GLOBAL AREA 

!)session information:login or logout privilazes,user records maintaining 

!!)stakes space: if u are diclaring a variable then the values been stack space 

!!!)sort area: entire operation done by within the sort area 

   baground process

              

                               System Monitor (SMON)

                  general server housekeeping functions.

Rollback: uncommited data stored in datafile will be roll back to redolog 

Roll forward: commited data which not stored in datafile will be recover from redolog file Process Monitor 

                               

                       (PMON)

monitors and manages individual user sessions .performs database locking/unlocking functions on UPDATE and DELETE query 

                           

                     DBWR (db writer)

DBwr write the dirty buffer images to respective datafiles and its used keep the dirty buffer cache free 

                      

when it accur 

!)check point accur 

 !!)even manual log switch occur

 !!!)commit 

 !v)every 1/3 full v) every 3 seconds 

 

  LGWR (logwriter)

to move the contents from redolog buffer cache to redolog files

  when it accur 

!)in every redolog buffer 1m full 

 !!)when redolog 1/3 full

 !!!)every 3 seconds 

 !v)commit accur V)check point accur

* log writer is the fastest baground process 

  

  archive process(ARCn) 

its optional baground process. its offline copy of online redolog file