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Database Instance startup and shutdown

Database Instance startup and shutdown. 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

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Database Instance startup and shutdown

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  1. Database Instance startup and shutdown A Guide to Oracle9i

  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 A Guide to Oracle9i

  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 A Guide to Oracle9i

  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. A Guide to Oracle9i

  5. Description of an instance A Guide to Oracle9i

  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. A Guide to Oracle9i

  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 A Guide to Oracle9i

  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. A Guide to Oracle9i

  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. A Guide to Oracle9i

  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. A Guide to Oracle9i

  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 A Guide to Oracle9i

  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. A Guide to Oracle9i

  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. A Guide to Oracle9i

  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 A Guide to Oracle9i

  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 A Guide to Oracle9i

  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. A Guide to Oracle9i

  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 Oracledatabase can be classified as: • Offline (cold) backups • Online (hot) backups A Guide to Oracle9i

  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 A Guide to Oracle9i

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