When this command is issued then oracle will not allow any new connections/sessions to the database and will kill the oracle instance in a abrupt manner. When this command is issued then oracle will not allow any new connections/sessions to the database and will wait for the users to commit/rollback their open transactions after which oracle will shut the database.Ī common scn number will be updated to controlfiles and datafiles before the database shuts down. When this command is issued then oracle will not allow any new connections/sessions to the database and will forcefully disconnect the existing connected users from the database and rollback all uncommited transactions and shut the database. There after it will save all the commited transactions and then shut the database.Ī common scn number will be updated to controlfiles and datafiles before the database shutsdown. When this command is issued then oracle will not allow any new connections/sessions to the database and will wait untill all the exising sessions log off. *the open state is used by the dba and programmers to work with the database in a normal way. *the mount state is used by the dba to perform recovery *the nomount state is used by the dba to create a new oracle database. If we want to drop the database then we mount the db it in this mode. This mode has been introduced from oracle 10g onwards. Quiesce a database gives us the opportunity to put our database in a single user mode without shutting down the database. Sql> select database_status from v$instance If we want to suspend all i/o operations. Sql> alter system enable restricted session Sql> alter system disable restricted session If we start an oracle database in restricted mode then only those users who have restricted session privilege will be able to connect to the database. If all the scn’s in the dbf’s are matched with the scn in the controlfile then the db can be opened for use.īut if any of the file scn is not matching with control file scn then oracle will ask to recover that file and database cannot be opened. We can directly go from a shut database to an open database by typing below command.Ģ) On opening a datafile oracle will check the scn in the file header with the scn in the control file. We can open an already mounted database by below command. In this case oracle will try to recover the database with automatic crash recovery, if that also fails then oracle will ask the dba to manually recover the datbase using media recovery methods. Incase the scns are not matched that means that the database is in an inconsistent state due to improper shutdown previously. IF the scn is the same then that file can be opened successfully, this way oracle will compare all the scns for all the files with the scn in the controlfile, only when all scns are matched with controlfile scn then only can the database be opened. If the sanity check is successful then oracle will begin to open each dbf one by one, when oracle opens the dbf it will check the scn (system change number) that is available in the dbf header and cross verify that scn with the scn in the controlfile. Incase any of the physical files is missing then sanity check will fail. Sanity check is nothing but reading the path and filenames of the dbf’s and log’s from the controlfile and checking wether those files are physically available in the same locations at the o/s level. To mount a database from a started state (nomount state)ġ) The mount state is used to recover a database that has crashed due to media failure.Ģ) The mount state is also used by the dba to enable archiver process.ģ) it is also used by the dba to create a standby controlfile for configuring a standby database using dataguard.Īfter mounting the database the dba can take the database to open state, when we open a database then a check will performed by oracle i.e, called sanity check. To mount a database directly from shutdown state we issue After opening the control file oracle will read the path of the datafiles and log files from the control file. In the mount state oracle will open the controlfile. Based on the values from this file oracle will allocate the sga in the RAM and start the background processes.Ĭommand to start database in nomount state:Ģ) Re-create a controlfile for an existing databaseįrom nomount the dba can take the database to mount state. The instance is created by reading all the values from a file known as init. When we start an oracle database in nomount state then oracle will create the oracle instance. We can bring database to nomount state from shutdown state. Each mode is used by the DBA’s to perform some specific operation in the database. An oracle database can be started in various modes.
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