Database Instance startup and shutdown

1
Database Instance startup and shutdown
2
client/server Architecture Distributed Processing

• Distributed Processing uses More than one
  processor to divide the processing for a set of
  related jobs
• It reduces the load on a single processor
• An Oracle database system can easily take
  advantage of Distributed Processing by using
  client/server Architecture
• In this architecture the database system is
  divided into two parts a. client portion
• b. server portion

3
client/server Architecture Distributed Processing

• The Client Portion interacts with a user through
  the keyboard, screen, mouse
• The client portion has no data responsibilities ,
  it concentrate on requesting and presenting data
  managed by the server portion
• The server portion runs oracle software and
  handles the functions required for shared data
  access
• The server receives and processes the SQL
  statements that comes from the client
  applications
• The computer that manages the server portion
  should have large disk capacity for fast
  processors

4
Introduction to an Oracle Instance

• Every running Oracle database is associated with
  an Oracle instance
• When a database is started on a database server,
  Oracle allocates a memory area called the System
  Global Area (SGA) and starts one or more Oracle
  processes
• This combination of the SGA and the Oracle
  processes is called an Oracle instance.

5
Description of an instance
6
The Instance and the Database

• After starting an instance, Oracle associates the
  instance with the specified database. This is a
  mounted database
• Multiple instances can run concurrently on the
  same computer, each accessing its own physical
  database
• Security for database startup and shutdown is
  controlled through connections to Oracle with
  administrator privileges. Normal users do not
  have control over the current status of an Oracle
  database.
• When a database is closed, users cannot access
  the information that it contains.

7
Parameter Files

• To start an instance, Oracle must read parameter
  files
• These files contain a list of configuration
  parameters for that instance and database.Example
  
• Parameters that name things, such as files
• Parameters that set limits, such as maximums
• The name of the database for which to start up an
  instance
• How much memory to use for memory structures in
  the SGA
• What to do with filled redo log files
• The names and locations of the database control
  files

8
Overview of Instance and Database Startup

• The three steps to starting an Oracle database
  and making it available for system wide use are
• Start an instance.
• Mount the database.
• Open the database.

9
How an Instance Is Started

• When Oracle starts an instance, it reads the
  parameter file to determine the values of
  initialization
• Then, it allocates an SGA, which is a shared area
  of memory used for database information and
  creates background processes
• At this point, no database is associated with
  these memory structures and processes.

10
How a Database Is Mounted

• The instance mounts a database to associate the
  database with that instance
• To mount the database, the instance finds the
  database control files and opens them
• Control files are specified in the CONTROL_FILES
  in the parameter file used to start the instance
  
• Oracle then reads the control files to get the
  names of the database's datafiles and redo log
  files.
• At this point, the database is still closed and
  is accessible only to the database administrator.

11
What Happens When You Open a Database

• Opening a mounted database makes it available for
  normal database operations. Any valid user can
  connect to an open database and access its
  information.
• When you open the database, Oracle opens the
  online datafiles and redo log files. If a
  tablespace was offline when the database was
  previously shut down, the tablespace and its
  corresponding datafiles will still be offline
  when you reopen the database

12
Instance Recovery

• If the database was last closed abnormally,
  because of a power failure, then Oracle
  automatically performs recovery when the database
  is reopened.

13
Overview of Database and Instance Shutdown

• The three steps to shutting down a database and
  its associated instance are
• Close the database.
• Unmount the database.
• Shut down the instance.

14
Close a Database

• When you close a database, Oracle writes all
  database data and recovery data in the SGA to the
  datafiles and redo log files, respectively
• Next, Oracle closes all online datafiles and redo
  log files
• At this point, the database is closed and
  inaccessible for normal operations. The control
  files remain open after a database is closed but
  still mounted

15
Unmount a Database

• After the database is closed, Oracle unmounts the
  database to disassociate it from the instance
• At this point, the instance remains in the memory
  of your computer
• After a database is unmounted, Oracle closes the
  control files of the database

16
Shut Down an Instance

• The final step in database shutdown is shutting
  down the instance. When you shut down an
  instance, the SGA is removed from memory and the
  background processes are terminated.

17
Database Backup and Recovery

• Important database administration support tasks
  include
• Backup creating a copy of the database files
• Recovery restoring the database to a working
  state after a hardware, software, Network,
  process or system malfunction
• Backup operations on an Oracle database can be
  classified as
• Offline (cold) backups
• Online (hot) backups

18
Database Backup and Recovery

• Offline Backup (cold backup) requires shutting
  down the database, then copying all of the
  database files to an alternate location
• Online Backup (hot backup) involves backing up
  critical database files while the instance is
  running, as well as creating an ongoing archive
  of database changes so the DBA can restore the
  database to its state at any point in time