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  Oracle Recovery Manager Facility

Oracle Tips by Burleson

Oracle8 introduced the recovery manager, rman, which can be thought of as the Enterprise Backup Utility on steroids. Oracle8i and Oracle have improved the usability and stability of rman. rman allows the backup of database files at the block level and automatically performs datafile compression by only backing up blocks that have been used or altered. In incremental mode, the rman only backs up blocks that have been altered or added in the database, greatly reducing the size of required backups.

 rman also allows the following:

* Scripting with rman script language, backup, and restore operations

* Reports on backup status and backup file status

* Use of a recovery catalog to facilitate backup and restore operations

* Parallelization of backup and restore operations

* Backup based on specified limits (i.e., amount of redo generated against a file)

* Backup of database, tablespace, or individual datafiles

* Batch backup operations

rman uses a recovery catalog. However, you can use rman without a catalog from just the data stored in the control files, but you are restricted to a subset of rman’s capabilities in this mode. The catalog contains information on the following:

* Datafile and archive log backup sets and pieces

* Datafile copies

* Archived redo logs and copies of them

* Tablespaces and datafiles at the target database

* Named, user-created sequences of commands called stored scripts

It is a good practice to maintain a small database strictly for the recovery catalog and perhaps the Enterprise Manager catalog files. The catalog should be resynchronized with all remote databases on a periodic basis. If you don’t use a catalog, you cannot do the following:

* Point-in-time recovery

* Use stored scripts

* Recovery if a control file is not available

rman creates backup sets that consist of backup pieces. Backup pieces are parts of the backup set at a size that is predetermined and usually based on the backup media capacity of operating system file-size limitations. Backup sets can be written to disk or secondary storage, can include a backup control file, and can span multiple OS files (pieces). Backup devices that are supported on your system are cataloged in the v$backup_device dynamic performance table.

rman backup sets that contain archive logs are called, appropriately enough, archivelog backup sets. With Oracle8, you cannot write archive logs directly to tape, but a job can be scheduled using rman to back archive log backup sets to tape or other storage.

rman produces either full or incremental backups. A full backup is a backup of one or more datafiles that contains all blocks of the datafile(s) that have been modified or changed. Full backups can be created out of:

* Datafiles

* Datafile copies

* Tablespaces (all datafiles for a tablespace)

* Archive logs

* Control files (current or backups)

* Entire databases

An incremental backup is a backup of one or more files and contains only blocks that have been modified. However, only complete control files are backed up in either incremental or full backups. Incremental backups can be made of:

* Datafiles

* Tablespaces

* Databases

The incremental backup allows the leveling of backups. Each level is denoted by an integer value, with the level of backup meaning that any blocks changed since the last incremental backup at this level will be backed up the next time this level is specified. This allows levels to be set based on timeframes; for example, 0 being a monthly full, 1 being a once-a-week incremental, and 2 being a daily incremental. Of course, this also leads to complicated rotation of tapes or backup media, taking us back to the good old towers-of-Hanoi backup scenario nightmares.

rman also allows for image copies of datafiles, archive logs, or control files. Image copies can only be made to disk and cannot contain multiple files.

rman allows report generation. Reports can be generated based on:

* Which files need backup

* Which files haven’t been backed up recently

* Which backup files can be deleted

Each backup set can be associated with a tag that can be used to identify it in subsequent operations. The tag doesn’t have to be unique. rman selects the most recent backup set in the case of backup sets with duplicate tags.

rman works against running or shutdown databases whether they are in archive log mode or not. However, if the database is not in archive log mode, the entire database can only be backed up if it was shut down cleanly. Tablespaces can only be backed up in NOARCHIVELOG mode if they are offline normal. There are no restrictions of this type on databases in ARCHIVELOG mode.

rman automatically detects corruptions and logs these in v$backup_corruption and v$copy_corruption dynamic performance tables. Corrupt blocks are still backed up.

Installing the rman Catalog

The catalog should be owned by a user with the resource role grant. I suggest a user in a small database dedicated to system administration functions such as the rman catalog and Enterprise Manager catalog. Create a tablespace for use by the rman user and assign that as the user’s default tablespace with unlimited quota. For example, if we wanted our user to be named rman_dba, the steps would be as follows:

sqlplus system/manager
 4: QUOTA UNLIMITED ON rman_data;
SQL>CONNECT rman_dba/rman_dba

Once the catalog has been built, the Recovery Manager can be utilized. The command is rman, rman80, or RMAN80, depending on your Oracle version and operating system (beginning with 8i, it will be only rman with no version identifier.) There are literally dozens of commands for use with the rman facility. I suggest reviewing the Oracle Backup and Recovery Concepts

Release 1 (9.0.1), Part Number A90133-02 (or most current release) (Oracle Corporation, June 2001) and Oracle Recovery Manager User's Guide Release 1 (9.0.1), Part Number A90135-01 (or most current release) (Oracle Corporation, June 2001) before using RMAN. In the remainder of this section I provide a sample scenario showing how the commands can be made into scripts.

Connection to RMAN in UNIX on early versions can be tricky. On some UNICES, the double quotation (“) character has to be escaped, and you need to use the double quotation to log in to rman (at least on early versions).  Assuming that the database to be backed up is ORTEST1 with a TNS alias of ORTEST1, the user is as specified earlier, and the catalog database is ORRMAN, the connection to RMAN for the user SYSTEM password MANAGER would look like this:

$ rman target ORTEST1 system/manager@ORTEST1  catalog rman_dbo/rman_dbo@ORRMAN

The target database service name in the tnsnames.ora file is ORTEST1. The recovery catalog database service name in the tnsnames.ora file is ORRMAN.

% cd $ORACLE_HOME/rdbms/admin
% sqlplus sys/change_on_install@ORRMAN
SQL> grant connect, resource to RMAN_DBA identified by RMAN_DBA;Grant succeeded.

SQL> connect rman/rman@ORRMAN
SQL> exit
% rman target sys/change_on_install@ORTEST1 catalog rman/rman@ORRMAN

Recovery Manager: Release - Beta
RMAN-06005: connected to target database: ORTEST1
RMAN-06008: connected to recovery catalog database
RMAN> register database;                           
RMAN-08006: database registered in recovery catalog
RMAN-08002: starting full resync of recovery catalog
RMAN-08004: full resync complete
RMAN> run    
2> {        
3> allocate channel c1 type disk;
4> backup full format '/oracle16/ORTEST1/amin/backup/backup%s%p' (database);
5> }
RMAN-08030: allocated channel: c1 

RMAN-08500: channel c1: sid=12 devtype=DISK 

RMAN-08008: channel c1: started datafile backupset
RMAN-08502: set_count=9 set_stamp=280246639 

RMAN-08011: channel c1: including current controlfile in backupset
RMAN-08010: channel c1: including datafile number 1 in backupset
RMAN-08010: channel c1: including datafile number 2 in backupset

RMAN-08010: channel c1: including datafile number 11 in backupset
RMAN-08010: channel c1: including datafile number 12 in backupset
RMAN-08013: channel c1: piece 1 created 

RMAN-08503: piece handle=/oracle16/ORTEST1/admin/backup/backup91 comment=NONE
RMAN-08003: starting partial resync of recovery catalog
RMAN-08005: partial resync complete
RMAN-10030: RPC call appears to have failed to start on channel default
RMAN-10036: RPC call ok on channel default
RMAN-08031: released channel: c1
RMAN> exit

Incomplete Restore Scenario  

The following shows the scenario for an incomplete recovery. The following scenario assumes that:

* You wish to do an incomplete recovery due to an application error that was made at a specific time.

* There are three tape drives.

* You are using a recovery catalog.

TIP:  It is highly advisable to back up the database immediately after opening the database resetlogs.

The following script restores and recovers the database to the time immediately before the user error occurred. The script does the following:

1. Starts the database mount and restricts connections to DBA-only users.

2. Restores the database files (to the original locations).

3. Recovers the datafiles either by using a combination of incremental backups and redo or just redo. Recovery Manager will complete the recovery when it reaches the transaction from the time specified.

4. Opens the database resetlogs.

Oracle recommends that you back up your database after the resetlogs (this is not shown in the example).

Ensure that you set your NLS_LANG and NLS_DATE_FORMAT environment variables. You can set these to whatever you wish—the date format of the following example is the standard date format used for recovery; for example, for UNIX (csh):

> setenv NLS_DATE_FORMAT 'YYYY-MM-DD:hh24:mi:ss'
       Next, start up SQLPLUS:
Sqlplus> connect sys as sysdba
password: xxxxxxx
SVRMGR> startup mount restrict

#  rman target internal/knl@prod1 catalog rman/rman@rcat cmdfile case2.rcv
run {
#  The 'set until time' command is for all commands executed 
#  between the { and } braces. Means both restore and recover
#  will both be relative to that point in time.
#  Note that Recovery Manager uses the Recovery Catalog to,
#  determine the structure of the database at that time, and
#  restore it.
    set until time '1997-06-23:15:45:00';
    allocate channel t1 type 'SBT_TAPE';
    allocate channel t2 type 'SBT_TAPE';
    allocate channel t3 type 'SBT_TAPE';
#  There is no need to manually catalog logs before recovery,
#  as Recovery Manager does catalog resync from the current
#  control file.
    sql 'alter database open resetlogs';

The preceding scenario is just an example of how to use the Recovery Manager. Please consult your manual before attempting to use the facility for production work. The RMAN readme file contains valuable insights into RMAN use and has several additional scenarios.

See Code Depot for Full Scripts

This is an excerpt from Mike Ault, bestselling author of "Oracle 10g Grid and Real Application Clusters".

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

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