Oracle Architectural Components

                                           Oracle  Architectural Components

The oracle architectural component includes a number of primary component like

1) Oracle server

2) Oracle instance

3) Oracle database

4)some mandatory file

5) some optional file

6) user and server process

7) other process

1) Oracle server: oracle server is combination of oracle instance and oracle database once we install oracle server software and then we create oracle database we called mission

2) Oracle instance: Oracle instance in nothing but collection of  SGA and background process, if instance is down we cannot access  data in existing database, instance down means memory have been release from operating system level,

some time getting issues for instance level failure ,means CPU utilisation its becomes 100% & memory utilisation it's become 100%

3) Oracle database: Database is collection of tree impotent file control file ,redo log file datafile

For the functionality of database at list one control file is required  and minimum no of online redo log group the required to create database or two and minimum the mandatory of datafile are required to create database or system.dbf and sysaux.dbf  

4) Some mandatory file: some mandatory background process is

1: DBWR  database writer

2: LGWR   log writer

3: CKPT    checkpoint

4: SMON  system monitor

5: PMON  process monitor

6: RECO     Recovery

5) Some optional file:some optional bg process is Archiver ,memory monitor(MMON),memory manager (MMAN),Rebalance activity  process (RBAL),Recovery writer

DBWR: database writer  to write  data to respective data file under the following situation when checkpoint occurs ,when time out occurs ,when there are no free buffer, when time out occurs, when make table space off line, when make table space read only mode, when you drop table, when you truncate table, when we keeps tables space begin backup mode

LGWR:write data in to online redo log file under the following situation  when redo buffer cache is 1/3 full, if user commit, for every 3 second

before DBWR write data to respective data file ,when ever log switch occurs checkpoint occurs which will be cast by CKPT process, during CKPT signal to DBWR to write data to respective data file

During CKPT check point update information with control file and data file header

SMON:when ever instance crash during next start-up smon perform instance recovery ,instance recovery is nothing but roll forwards and roll backwards, in order to perform instance recovery smon is going to scan the redo and undo

Roll backwards: means  removing the uncommitted transaction data with respective data file

 Roll forwards: means writing a complete transactional data from online redo log file to the respective data file

PMON: background process continually monitor all user process, if any one of user process  get terminated withought  releasing lock PMON release lock and rollback the transition

6) user and server process: The user and server process are the primary process involved when a SQL statement is executed however ,other process may help the server complete processing of sql statements