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Lesson 13

Performing Physical Backups with and without Archiving-Conclusion

  1. with Archiving and
  2. without Archiving
This module introduced you to various methods of performing physical backups with and without archiving.
You learned how to do open and closed database backups. You also learned the importance of frequent and regular database and tablespace backups as essential strategies for any recovery scheme.
Having completed this module, you should be able to:
  1. Perform database backups using operating system commands
  2. Describe the recovery implications of closed and open database backups
  3. Perform closed and open database backups
  4. Identify the different types of control file backups
  5. Identify the backup implications of the logging and nologging options
  6. Describe backup issues associated with read-only tablespaces

Backup Recovery Glossary Terms

This module introduced you to the following terms:
  1. Database Writer: The Database Writer is responsible for writing modified blocks from the database buffer cache back to the database files.
  2. System change number: System change number is a clock value for the Oracle database that describes a committed version of the database. It functions as a timestamp that helps to ensure transaction consistency.
  3. Media failure: Media failure refers to the error that occurs when you try to write or read a file that is required to operate the database. It is also called disk failure because there is a physical problem reading or writing physical files on the disk. Mirrored online redo logs: A mirrored online redo log is also called a multiplexed online redo log. It contains copies of online redo log files physically located on a separate disk. Any changes made to one member of the group are recorded in other members.
  4. Operating system backup: An operating system (O/S) backup is made using an operating system command. Operating system backups can be written to disk or tape in any format that a specific operating system supports.
  5. Control file: A control file is a binary file containing the name and creation time of the database, the names and locations of a database's datafiles and redo log files. Every time an instance of the database is started, its control file is used to identify the datafile and redo log file that must be open for the database to run properly.
In the next module, you will learn how to recover a database in NOARCHIVE mode in case of media failure. The following section discusses data dictionary views and their functions.

Data Dictionary Views useful for Backup Operations

V$RECOVER_FILE view

  1. V$DATAFILE: Contains a list of the names and status for all datafiles
  2. V$CONTROLFILE: Contains the names of all control files
  3. V$LOGFILE: Contains the names of all redo log files
  4. V$BACKUP: Contains information about which files are in backup mode
  5. V$ARCHIVE_LOG: Contains archived log information from control files
  6. V$ARCHIVE_DEST: Contains information about the current instance and archive log destinations
  7. V$LOG_HISTORY: Contains log file information from the control file
  8. V$DATABASE: Contains information about the current state of archiving
  9. DBA_DATA_FILES: Contains a list of all datafiles and their respective tablespaces

You can view data file numbers and data file names in the V$DATAFILE, V$DATAFILE_COPY, or V$DATAFILE_HEADER view. For example, to view data file numbers and data file names in your database, issue this SQL command:
RMAN> select file#, name from v$datafile;
You can also issue the RMAN report schema command to display data file names and numbers. Once you know the name or number for each file you want to back up, you can use the backup datafile command to perform the actual backup operation.

Does the missing data file physically exist?

Before you restore the data file from the RMAN backup, verify whether the missing data file physically exists at the OS level. Also confirm that the Oracle software owner has the appropriate read and write privileges on the missing data file and directory. We also recommend querying the data dictionary for more information. The V$DATAFILE_HEADER view derives its information from the data file headers and reports in the ERROR and RECOVER columns any potential problems.For example, a YES or null value in the RECOVER column indicates there is a problem:

Verify whether the missing data file physically exists at the OS level
1) Verify whether the missing data file physically exists at the OS level

Also the V$RECOVER_FILE view displays the status of files needing media recovery. The V$RECOVER_FILE reads from the control file and displays information about files needing media recovery:
V$RECOVER_FILE view displays the status of files needing media recovery
2) V$RECOVER_FILE view displays the status of files needing media recovery

Note I f you restore a control file from a backup, the V$RECOVER_FILE view will not contain accurate information.
Question: I want to display the maxsize for a tablespace data file.
Maxsize is the total of maxsize of datafiles in that particular tablespace which is the total of Megabytes allocated to the datafiles.
For example,
alter database datafile 'file1' size 10G autoextend on maxsize 32G;
alter database datafile 'file2' size 15G autoextend on maxsize 32G;

Normal tablespace scripts including the one on this site is having total of size of datafiles (that is 10g + 15g = 25g).
I am looking for script which will use maxbytes of datafiles (that is 32g + 32g = 64g).

Consistent and Inconsistent Backups

A backup is either consistent or inconsistent. To make a consistent backup, your database must have been shut down cleanly and remain closed for the duration of the backup. All committed changes are written to the data files during the shut down process, so the data files are in a transaction-consistent state. When you restore your data files from a consistent backup, you can open the database immediately. If the database is in ARCHIVELOG mode, then you can make inconsistent backups that are recoverable using archived redo log files. Open database backups are inconsistent because the online redo log files contain changes not yet applied to the data files. The online redo log files must be archived and then backed up with the data files to ensure recoverability. Despite the name, an inconsistent backup is as robust a form of backup as a consistent backup. The advantage of making inconsistent backups is that you can back up your database while the database is open for updates.

Archiving Physical Backups - Quiz

Click the Quiz link below to review your understanding of physical backups with and without archiving.
Archiving Physical Backups - Quiz

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