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ORACLE DBA INTERVIEW QUESTIONS

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3+ YEARS OF ORACLE DBA INTERVIEW QUESTIONS WITH ANSWERS
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  1)   What is snapshot control file in RMAN ? SNAPSHOT CONTROLFILE  A snapshot control file is created by RMAN during the backup process that serves as a point-in-time copy of the database control file. This will ensure that that backups  being taken is consistent to a given point in time. For example, if you add a datafile or tablespace to a database after the backup has started, (assuming an online backup and  before the backup has ended), that datafile and/or tablespace will not be included in the backup. It is sometimes required that the location and name of the snapshot control file be changed from its default. To set the snapshot control file to a different location (and name) use the following: RMAN> CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/orabackup/rman/ORA920/scontrolfile.ctl';   NOTE:  The default value for the snapshot control file name is platform-specific and dependent on the Oracle home. For example, the default on some UNIX system is ?/dbs/snapcf_@.f . If you clear the control file name, and you change the Oracle home, then the default location of the snapshot control file changes as well.  As RMAN needs a consistent view of the control file it takes a backup of the controlfile by creating a snapshot and during the backup RMAN uses the snapshot of the controlfile. By default the snapshot controlfile is created in $ORACLE_HOME/dbs/snapcf_ORACLE_SID.f which can be changed by setting the following parameter in RMAN $ rman target / —  display parameter value RMAN> show all; .. CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/10.2.0.4/TESTDB/snapcf_TESTDB.f'; # default —  set to new path for controlfile snapshot RMAN> CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u02/TESTDB/snapcf_TESTDB.f';  When multiple RMAN are running one could run into an issue RMAN-08512 where RMAN is waiting for getting a lock on snapshot controlfile header. To find the session run the following SQL. SELECT vs.sid, vs.username, vs.program, vs.module, TO_CHAR(vs.logon_time, 'DD-MON-YYYY HH24:MI:SS') FROM v$session vs, v$enqueue_lock vel WHERE vs.sid = vel.sid AND vel.type = 'CF' AND vel.id1 = 0 AND vel.id2 = 2 Configuring the Snapshot Control File  The snapshot control fileis a temporary file that is created at a certain location specified over the operating system. This file is used by RMAN to synchronize the information with the current control file. This file, except for synchronizing the information with the current control file, does not do anything else and hence, is not included in the recovery catalog. It does not contain any information about the current backup that you have taken, though it does know about the last backups that were done and are not marked yet as obsolete. So this file can be used to recover a scenario where you have lost everything and also were not using the catalog. You can use the last backup information recorded in this file and can recover the database with that backup. The location of this file depends on the platform and also uses a default naming convention as well. Interestingly, irrespective of the flash recovery area being configured, the snapshot control file does not use it and is set for the location, normally to the ORACLE_HOME/database or ORACLE_HOME/dbs location with the name sncf<sid>.ora. You can see the current name and location of the file by the show command. RMAN> show snapshot controlfile name;  RMAN configuration parameters are: configure snapshot controlfile name to 'E:\ORACLE\product\10.2.0\db_1\database\sncforcl.ora'; # default  In this case, it is set to the default location. You can change it using the configure command.  2)   How To Register Older Backups To RMAN Catalog  W   henever backups were taken using the OS utility the backup information is not updated in the repository.Only the backups taken using rman utility were updated in the catalog.To update the catalog about the backup information took @ os level we can use the catalog command. . Cataloging Older Files in the Recovery Catalog   RMAN> CATALOG DATAFILECOPY '/disk1/old_datafiles/01_01_2003/users01.dbf';   RMAN> CATALOG ARCHIVELOG '/disk1/arch_logs/archive1_731.dbf', '/disk1/arch_logs/archive1_732.dbf';   RMAN> CATALOG BACKUPPIECE '/disk1/backups/backup_820.bkp';   You can also catalog multiple backup files in a directory at once, using the CATALOG START WITH command, as shown in this example:   RMAN> CATALOG START WITH '/disk1/backups/';   RMAN lists the files to be added to the RMAN repository and prompts for confirmation before adding the backups.   Be careful when creating your prefix for CATALOG START WITH. RMAN scans all paths for all files on disk which begin with your specified prefix. The wrong prefix may include more files than you intend. For example, a group of directories /disk1/backups , /disk1/backups-year2003, /disk1/backupsets, and /disk1/backupsets/test and so on, all contain backup files. The command   RMAN> CATALOG START WITH '/disk1/backups';   catalogs all files in all of these directories, because /disk1/backups is a prefix for the paths for all of these directories. In order to catalog only backups in the /disk1/backups directory, the correct command would be:   RMAN> CATALOG START WITH '/disk1/backups/'; 3)   How to catalog and uncatalog a backup to   RMAN repository    4)   Catalog Backup      Whenever we take any backup through RMAN, in the repository information of the backup is recorded. The RMAN respository can be either controlfile or recovery catalog. However if I take a  backup through OS command then RMAN does not aware of that and hence recorded are not reflected in the repository. This is also true whenever we create a new controlfile or a backup taken by RMAN is transferred to another place using OS command then controlfile/recovery catalog does not know about the prior backups of the database. So in order to restore database  with a new created controlfile we need to inform RMAN about the backups taken before so that it can pick one to restore. This task can be done by catalog command in RMAN. With catalog command it can -Add information of backup pieces and image copies in the repository that are on disk. -Record a datafile copy as a level 0 incremental backup in the RMAN repository. -Record of a datafile copy that was taken by OS.   But CATALOG command has some restrictions. It can't do the following. -Can't catalog a file that belong to different database. -Can't catalog a backup piece that exists on an sbt device. Examples of Catalog command     1)Catalog an archive log: To catalog two archived logs named /oracle/oradata/arju/arc001_223.arc and /oracle/oradata/arju/arc001_224.arc the command is, RMAN>CATALOG ARCHIVELOG '/oracle/oradata/arju/arc001_223.arc', '/oracle/oradata/arju/arc001_224.arc';  2)Catalog a file copy as an incremental backup: To catalog datafile copy '/oradata/backup/users01.dbf' as an incremental level 0 backup your command will be, RMAN>CATALOG DATAFILECOPY '/oradata/backup/users01.dbf' LEVEL 0;  Note that this datafile copy was taken backup either using the RMAN BACKUP AS COPY command, or by using operating system utilities in conjunction with ALTER TABLESPACE BEGIN/END BACKUP. 3)Catalog multiple copies in a directory: To catalog all valid backups from directory /tmp/backups issue, RMAN>CATALOG START WITH '/tmp/backups' NOPROMPT;  4)Catalog files in the flash recovery area: To catalog all files in the currently enabled flash recovery area without prompting the user for each one issue, RMAN>CATALOG RECOVERY AREA NOPROMPT;  5)Catalog backup pieces: To catalog backup piece /oradata2/o4jccf4 issue, RMAN>CATALOG BACKUPPIECE '/oradata2/o4jccf4'; Uncatalog Backup     In many cases you need to uncatalog command. Suppose you do not want a specific backup or copy to be eligible to be restored but also do not want to delete it. To uncatalog all archived logs issue, RMAN>CHANGE ARCHIVELOG ALL UNCATALOG;  To uncataog tablespace USERS issue, RMAN>CHANGE BACKUP OF TABLESPACE USERS UNCATALOG;  To uncatalog a backuppiece name /oradata2/oft7qq issue, RMAN>CHANGE BACKUPPIECE '/oradata2/oft7qq' UNCATALOG   5)   What is Database Incarnation ?  
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