1. Backup and Recovery Part 2

2. Online backup Online backup requirements: Backup all data files (file system copy) Backup all redo information produced during online backup Backup control file (using database commands)

3. Online backup Online backup procedure: Remember current log sequence (v$log view) For each tablespace: Activate tablespace backup mode Copy tablespace data files to backup location Deactivate tablespace backup mode Force archival of active redo log (for example: force logfile switch) Backup all redo logs produced since backup started Backup control file

4. Tablespace backup mode To activate tablespace backup mode: ALTER TABLESPACE tablespace_name BEGIN BACKUP To deactivate tablespace backup mode: ALTER TABLESPACE tablespace_name END BACKUP Notes: Data files should not be copied unless tablespace is in backup mode Backup mode results in: Data header not being updated (it is updated at backup end) Larger redo log records (more redo logs produced)

5. Archiving redo logs The following commands are useful for online backups: ALTER SYSTEM ARCHIVE LOG ALL; ALTER SYSTEM ARCHIVE LOG NEXT; ALTER SYSTEM ARCHIVE LOG SEQUENCE 104; ALTER SYSTEM ARCHIVE LOG CURRENT; ALTER SYSTEM ARCHIVE LOG CURRENT NOSWITCH; (when database is mounted) To activate/deactivate automatic archival: ALTER SYSTEM ARCHIVE LOG START; ALTER SYSTEM ARCHIVE LOG STOP;

6. Control file backup Control file cannot be backed up using operating system commands Control file must be backed up using database commands: ALTER DATABASE BACKUP CONTROLFILE TO TRACE; ALTER DATABASE BACKUP CONTROLFILE TO ‘c:\backup\control.ctl'

7. Backup controlfile During recovery backup controlfile should be used only when necessary Recovery with backup controlfile should be indicated: RECOVER DATABASE USING BACKUP CONTROLFILE; RECOVER DATABASE USING BACKUP CONTROLFILE UNTIL CANCEL; During backup controlfile recovery: Database does not know if recovery is complete or not ALTER DATABASE OPEN must include RESETLOGS or NORESETLOGS

8. Using online backup Online backup can be used to: Do complete recovery, in that case: Restore required data files, do normal recovery Do point in time or change based recovery, in that case: Restore all data files, do recovery UNTIL TIME or UNTIL CHANGE Do minimal recovery (open the database in the state just after backup), in that case: Restore all data files, do recovery UNTIL CANCEL Apply only the logs produced during backup OPEN DATABASE with RESETLOGS option

9. Archive destination Archived log files can be multiplexed (up to 10 locations): Initialization parameter LOG_ARCHIVE_DEST_n specifies archive destination for each location Archival destination can be: Local filesystem path Files are simply copied to that destination Network service name (remote archival) Files are sent via network to remote standby database Destination can be MANDATORY or OPTIONAL

10. Archive destination Archival destination examples: LOG_ARCHIVE_DEST_1 = 'LOCATION=C:\backup MANDATORY' LOG_ARCHIVE_DEST_2 = 'SERVICE=remote1 OPTIONAL' LOG_ARCHIVE_DEST_3 = 'LOCATION=C:\backup2' LOG_ARCHIVE_DEST_4 = 'SERVICE=remote2 OPTIONAL REOPEN=30 MAX_FAILURE=10'

11. Archive destination LOG_ARCHIVE_MIN_SUCCEED_DEST: Specifies minimum number of OPTIONAL destinations that must succeed

12. Archived log file name LOG_ARCHIVE_FORMAT: Specifies file name format, must include: %s – log sequence %t – thread number (used in clusters) %r – resetlogs id Example: LOG_ARCHIVE_FORMAT=arch%t_%s_%r.arc

13. Archiving – useful views V$DATABASE – specifies archival mode V$ARCHIVED_LOG – historical achived log information from control file V$ARCHIVE_DEST – archival destinations, mode and status of each destination V$BACKUP_REDOLOG – information about backups of redo logs V$LOG – information about online log groups V$LOG_HISTORY – information about which logs have been archived and SCN range for each archived log

14. V$DATABASE V$DATABASE – columns related to recovery: DBID - Database identifier generated when the database is created and stored in all file headers CURRENT_SCN – current System change number RESETLOGS_CHANGE# - System change number (SCN) at open resetlogs RESETLOGS_TIME - Timestamp of open resetlogs LOG_MODE – archivelog or noarchivelog CHECKPOINT_CHANGE# - Last SCN checkpointed OPEN_RESETLOGS - (NOT ALLOWED | ALLOWED | REQUIRED)