|Oracle8i Backup and Recovery Guide
The action that occurs when the redo log entry marking the checkpoint changes. For example, the CKPT process logs redo record 356 as the checkpoint, then three seconds later records redo record 358 as the checkpoint.
A copy of one of the filled members of an online redo log group made when the database is in ARCHIVELOG mode. As the LGWR process fills each online redo log with redo records, Oracle copies the log to one or more offline archive log destinations. This copy is the archived redo log, also known as the offline redo log.
The mode of the database in which Oracle copies filled online redo logs to disk. Specify the mode at database creation or by using the ALTER DATABASE command. You can enable automatic archiving either dynamically using the ALTER SYSTEM command or by setting the initialization parameter LOG_ARCHIVE_START to TRUE.
Running your database in ARCHIVELOG mode has several advantages over NOARCHIVELOG mode. You can:
To protect your ARCHIVELOG mode database in case of failure, back up your archived logs.
The operation in which the ARCn background process copies filled online redo logs to offline destinations. You must run the database in ARCHIVELOG mode to archive redo logs.
A unit that contains one or more tape drives, a robotic arm, and a shelf of tapes. The ATL, also called a tape silo, is able to load and unload tapes into the tape drive from the shelf without operator intervention. More sophisticated tape libraries are able to identify each tape; for example, the robotic arm can use a bar-code reader to scan each tape's barcode and identify it.
See Also: media manager
(1) A database created from target database backups using the RMAN duplicate command.
(2) A temporary database that is restored to a new location and then started up with a new instance name during tablespace point-in-time recovery (TSPITR). A TSPITR auxiliary database contains the recovery set and auxiliary set.
In TSPITR, the set of files that is not in the recovery set but which must be restored in the clone database for the TSPITR set to be successful. These auxiliary files include:
(1) A copy of data, i.e., a database, tablespace, table, datafile, control file, or archived redo log. You can make a backup by:
(2) An RMAN command that creates a backup set. The output of a backup command is only usable by RMAN; the output of the RMAN copy command can be used without additional processing.
See closed backup
A backup of the control file. Make the backup by:
Typically, you restore backup control files when all copies of the current control file are damaged; sometimes you restore them before performing certain types of point-in-time recovery.
See Also: control file
A backup piece is a physical file in an RMAN-specific format that belongs to only one backup set. A backup set usually contains only one backup piece. The only time RMAN creates more than one backup piece is when you limit the piece size a set limit kbytes command. Use this command when the storage or media manager you are writing your backup to is not able to support writing a file larger than a certain size.
An RMAN-specific logical grouping of one or more physical files called backup pieces. The output of the RMAN backup command is a backup set. Extract the files in a backup set by using the RMAN restore command. You can multiplex files into a backup set, i.e., intermingle blocks from input files into a single backup set.
There are two types of backup sets:
The termination of a disk mirroring procedure so that a mirror image is no longer kept up-do-date. You can create operating system database backups by placing the tablespaces in the database in hot backup mode and then breaking the mirror. After taking the tablespaces out of hot backup mode, back up the broken mirror side to tape. After the backup is complete, you can resilver the mirror.
The portion of the SGA that holds copies of data blocks read from datafiles. All user processes concurrently connected to the instance share access to the database buffer cache.
The buffers in the cache are organized in two lists: the dirty list and the least recently used (LRU) list. The dirty list holds dirty buffers, which contain data that has been modified but has not yet been written to disk. The least recently used (LRU) list holds free buffers (unmodified and available), pinned buffers (currently being accessed), and dirty buffers that have not yet been moved to the dirty list.
See Also: SGA (System Global Area)
A type of incomplete media recovery in which you use the RECOVER command with the UNTIL CANCEL clause. Recovery proceeds until you issue the CANCEL command.
A single change to a single data block. A change vector is the smallest unit of change recorded in the redo log.
See Also: redo record
A type of incomplete media recovery that recovers up to a specified SCN. You can also perform cancel-based recovery, which recovers until you issue the CANCEL command, and time-based recovery, which recovers to a specified time.
A connection between Recovery Manager and the target database. Each allocated channel starts a new Oracle server session; the session then performs backup, restore, and recovery operations. The type of channel determines whether the Oracle server process will attempt to read or write and whether it will work through a third-party media manager. If the channel is of type:
Channels are always able to read and write datafiles to and from disk, no matter what their type.
A pointer indicating that all changes prior to the SCN specified by a redo record have been written to the datafiles by DBWn. Each redo record in the redo log describes a change or a set of atomic changes to database blocks; a checkpoint for a redo entry confirms that the changes described in previous redo entries have been written to disk, not just to memory buffers. The background process CKPT automatically records a checkpoint in the control file every three seconds.
A numeric value that is mathematically derived from the contents of an Oracle data block. The checksum allows Oracle to validate the consistency of the block.
See Also: data block
A database shut down with the IMMEDIATE, TRANSACTIONAL, or NORMAL options of the SHUTDOWN command. A database shut down cleanly does not require recovery; it is already in a consistent state.
A backup of one or more database files taken while the database is closed. Typically, closed backups are also whole database backups. If you closed the database cleanly, then all the files in the backup are consistent. If you shut down the database using a SHUTDOWN ABORT or the instance terminated abnormally, then the backups are inconsistent.
A database that is not available to users for queries and updates. When the database is closed you can start the instance and optionally mount the database.
See Also: open database
See closed backup
A file containing a sequence of RMAN commands that you can run from the command line. The contents of the command file should be identical to commands entered at the command line.
The recovery of a database by applying all online and archived redo generated since the restored backup. Typically, you perform complete media recovery when media failure damages one or more datafiles or control files. You fully recover the damaged files using all redo generated since the restored backup was taken. If you use RMAN, you can also apply incremental backups during complete recovery.
The process of copying only used data blocks into RMAN backup sets. A newly created datafile contains many never-used blocks. When RMAN creates backup sets, it only includes blocks that have been used; it follows that RMAN does not write never-used blocks into backup sets.
A whole database backup that you can open with the RESETLOGS option without performing media recovery. In other words, you do not need to apply redo to any datafiles in this backup for it to be consistent. All datafiles in a consistent backup must:
You can only take consistent backups after a database has been shut down cleanly. The database must not be opened until the backup has completed.
A binary file associated with a database that maintains the physical structure and timestamps of all files in that database. Oracle updates the control file continuously during database use and must have it available for writing whenever the database is mounted or open.
(1) To replicate data. You make copies of Oracle datafiles, control files, and archived redo logs in two ways:
(2) A Recovery Manager command that makes a replica of a database's datafiles, control file, or archived redo logs. This replica is made by an Oracle server process, allocated to a Recovery Manager channel, which reads the Oracle file and writes a replica out to disk. Recovery Manager can copy the files of an open database without putting the tablespaces into hot backup mode.
In RMAN, the datafile in the target database pointed to by the control file. You can make a backup datafile current again by executing a switch command.
An Oracle block that is not in a recognized Oracle format, or whose contents are not internally consistent. Oracle identifies corrupt blocks as one of two types:
You can only repair a media corrupted block by:
If media corruption is due to faulty hardware, neither solution will work until the hardware fault is corrected.
A datafile that contains one or more corrupt blocks.
See Also: corrupt block
The automatic application of online redo records to a database after either a single-instance database crashes or all instances of an OPS database crash. Crash recovery only requires redo from the online logs: archived redo logs are not required.
In crash recovery, an instance automatically recovers the database before opening it. In general, the first instance to open the database after a crash or SHUTDOWN ABORT automatically performs crash recovery.
A check to determine whether files on disk or in the media management catalog correspond to the information in the recovery catalog (if used) and the control file. Because the media manager can mark tapes as expired or unusable, and because files can be deleted from disk or otherwise become corrupted, the recovery catalog and control file can contain outdated information about backups and image copies.
Use change ... crosscheck when you want to provide a list of backup sets or pieces to check; use crosscheck backupset when you wish to restrict the crosscheck to a specified device type, object type, or date range and let RMAN generate the list of backup sets or pieces. To determine whether you can restore a file, use validate or restore ... validate.
An incremental backup that backs up all the blocks changed since the most recent backup at level n-1 or lower. For example, in a cumulative level 2 backup, RMAN determines which level 1 or level 0 backup is most recent and then backs up all blocks changed since that backup.
The control file on disk; it is the most recently modified control file for the current incarnation of the database. For a control file to be considered current during recovery, it must not have been restored from backup.
See Also: control file
The online redo log file in which the LGWR background process is currently logging redo records. Those files to which LGWR is not writing are called inactive.
Every database must contain at least two online redo log files. If you are multiplexing your online redo log, LGWR concurrently writes the same redo data to multiple files. The individual files are called members of an online redo log group.
The smallest unit of data in an Oracle database, the size of which is determined by the parameter DB_BLOCK_SIZE at database creation.
See Also: corrupt block
The recovery of a database to a specified non-current time, SCN, or log sequence number.
A datafile is a physical O/S file on disk that was created by Oracle and contains data structures such as tables and indexes. A datafile can only belong to one database.
See Also: inaccessible datafile
A copy of a datafile on disk produced by either:
An internal, uniquely generated number that differentiates databases. Oracle creates this number automatically when you create the database.
A type of incremental backup that backs up all blocks that have changed since the most recent backup at level n or lower. For example, in a differential level 2 backup RMAN determines which level 2, level 1, or level 0 backup is most recent and then backs up all blocks changed since that backup. Differential backups, also called non-cumulative incremental backups, are the default type of incremental backup.
A database created from target database backups using the RMAN duplicate command.
See Also: auxiliary database
The extraction of logical data (i.e., not physical files) from a database using the Export utility. You can then use the Import utility to import the data into a database.
See Also: full export
The first block of an Oracle datafile. The file header contains bookkeeping information related to the file, including the checkpoint SCN. Oracle requires media recovery when the checkpoint SCN in the datafile header does not match the file header information stored in the control file.
See Also: checkpoint
A type of media corruption that can occur when DBWn is writing a block at the same time an O/S utility is reading the block for backup. The block that the O/S reads can be split, i.e., the top of the block is written at one point in time while the bottom of the block is written at another point in time. If you restore a file containing a fractured block and Oracle reads the block, then the block is considered corrupt.
The potential for fractured blocks necessitates putting tablespaces in hot backup mode before O/S online backups. A database in hot backup mode writes whole Oracle data blocks to the redo log, so that if a block is split during the backup, you can repair it by using redo. Recovery Manager does not experience this problem because the server process performing the backup or copy reads each block to determine whether it is split and re-reads the block until it gets a consistent version.
A non-incremental RMAN backup. Note that "full" does not refer to how much of the database is backed up, but to the fact that the backup is not incremental. Consequently, you can make a full backup of one datafile.
The only difference between a full backup and an incremental level 0 backup is that the full backup will not affect the number of blocks backed up by any subsequent incremental backup.
See Also: incremental backup
An export of the whole database.
See Also: export
A Recovery Manager operation that updates the recovery catalog with all changed information in the database's control file. You can initiate full catalog resynchronizations by issuing the RMAN command resync catalog. Recovery Manager initiates resync operations as needed when executing certain commands.
A datafile that contains at least one block with an SCN more recent than the checkpoint SCN in its header. For example, this situation occurs when Oracle updates a datafile that is in hot backup mode. A fuzzy file that is restored always requires recovery.
See open backup
The database mode initiated when you issue the ALTER TABLESPACE tablespace_name BEGIN BACKUP command before taking an open backup. You take a tablespace out of hot backup mode when you issue the ALTER TABLESPSACE tablespace_name END BACKUP command.
You must use this command when you make an O/S backup of one or more datafiles in an online tablespace. Recovery Manager does not require you to put the database in hot backup mode. Updates to tablespaces in hot backup mode create more than the usual amount of redo because each change causes Oracle to write the entire block rather than just the changed data to the redo log.
A copy of a single datafile, archived redo log file, or control file that is:
See Also: copy
A datafile that Oracle is attempting to read, but cannot find. Attempts to access an inaccessible file result in errors. Typically, a file is inaccessible because the media on which it is stored is faulty or the file has been moved or deleted.
A redo log file that is not required for instance recovery because the changes contained in its redo records have already been applied to the database. The current redo log file is never inactive. If you operate your database in ARCHIVELOG mode, the ARCn process archives inactive redo log files.
A separate version of a physical database. The incarnation of the database changes when you open it with the RESETLOGS option. Make a whole database backup of all files that are not offline-clean or read-only after opening with the RESETLOGS option. If using RMAN, issue the reset database command after opening in RESETLOGS mode.
The recovery of a database in which you do not apply all of the changes generated since you created the restored backup.
Incomplete recovery is usually performed when:
The requirement is to recover up until some point in time before an incorrect action occurred in the database. For example, a user mistakenly deletes payroll transactions before the transactions are sent to the payroll agency. In this example, the DBA will need to restore the whole database and then perform incomplete recovery up until the point just before the user deleted the transactions.
An archived redo log which is needed for complete recovery was not backed up, or the archived redo log contents are corrupt. In this case, you only option is to recover up to the missing log.
In each case, open the database with the RESETLOGS option after performing media recovery. If you use RMAN with a recovery catalog, you must also reset the database.
A backup in which some of the files in the backup contain changes that were made after the files were checkpointed. This type of backup needs recovery before it can be made consistent. Inconsistent backups are usually created by taking open database backups; that is, the database is open while the files are being backed up. You can also make an inconsistent backup by backing up datafiles while a database is closed, either:
Note that inconsistent backups are only useful if the database is in ARCHIVELOG mode.
An RMAN backup in which only modified blocks are backed up. Incremental backups are classified by level. An incremental level 0 backup performs the same function as a full backup in that they both back up all blocks that have ever been used. The difference is that a full backup will not affect blocks backed up by subsequent incremental backups, whereas an incremental backup will affect blocks backed up by subsequent incremental backups.
Incremental backups at levels greater than 0 back up only blocks that have changed since previous incremental backups. Blocks that have not changed are not backed up.
Incremental backups are divided into two types: differential and cumulative. Differentials back up all blocks that have changed since the most recent backup at level n or lower. For example, a differential level 2 backup backs up all blocks modified since a previous level 2, level 1, or level 0 backup, whichever is most recent. Cumulative backups back up all the blocks used since the most recent backup at level n-1 or lower. For example, a cumulative level 2 backup backs up all blocks modified since a previous level 1 or level 0 backup, whichever is most recent.
An SGA, Oracle code, and background processes. Create an instance by issuing any of the following commands:
An instance is stopped by issuing a SHUTDOWN statement.
See Also: SGA (System Global Area)
In an OPS configuration, the application of redo data to an open database by an instance when this instance discovers that another instance has crashed. A surviving instance automatically uses the redo log to recover the data in the instance's buffer cache. Oracle undoes any uncommitted transactions that were in progress on the failed instance when it crashed and then clears any locks held by the crashed instance after recovery is complete.
RMAN commands such as backup, copy, and recover that you must execute within the brackets of a run command.
See Also: stand-alone commands
A utility that allows you read information contained in online or archived redo logs based on various selection criteria. For example, you can select information from the V$LOGMINER_CONTENTS view that enables you to:
See Also: archived redo log
A number that uniquely identifies a set of redo records in a redo log file. When Oracle fills one online redo log file and switches to a different one, Oracle automatically assigns the new file a log sequence number. For example, if you create a database with two online log files, then the first file is assigned log sequence number 1. When the first file fills and Oracle switches to the second file, it assigns log sequence number 2; when it switches back to the first file, it assigns log sequence number 3, and so forth.
For RMAN, a type of incomplete recovery that recovers up to a specified log sequence number.
See Also: incomplete recovery
The point at which LGWR stops writing to the active redo log file and switches to the next available redo log file. LGWR switches when either the active log file is filled with redo records or you force a switch manually.
If you run your database in ARCHIVELOG mode, Oracle archives the redo data in inactive log files into archived redo logs. When a log switch occurs and LGWR begins overwriting the old redo data, you are protected against data loss because the archived redo log contains the old data. If you run in NOARCHIVELOG mode, Oracle overwrites old redo data at a log switch without archiving it. Hence, you lose all old redo data.
See Also: redo log
Backups in which the Export utility uses SQL to read database data and then export it into a binary file at the O/S level. You can then import the data back into a database using the Import utility.
Backups taken with the Export utility differ in the following ways from RMAN backups:
See Also: physical backups
A mode of a standby database in which the standby waits for archived log files from a target database and then automatically applies the redo logs once the files become available. This feature eliminates the need for you to interactively provide the recovery process with filenames of the archived redo logs.
See Also: standby database
A physical problem that arises when Oracle fails in its attempt to write or read a file that is required to operate the database. A common example is a disk head crash that causes the loss of all data on a disk drive. Disk failure can affect a variety of files, including the datafiles, redo log files, and control files. Because the database instance cannot continue to function properly, it cannot write the data in the buffer cache of the SGA to the datafiles.
A utility provided by a third party vendor that is capable of actions such as loading, labelling and unloading sequential media such as tape drives. Media managers also allow you to configure media expiration and recycling, and may also have the ability to control Automated Tape Libraries (ATLs).
See Also: ATL (automated tape library)
An Oracle published API to which media management vendors have written compatible software libraries. This software integrates with Oracle so that an Oracle server process is able to issue commands to the Media Manager to write backup files to sequential storage, and read files from sequential storage. When Oracle issues a request to backup or restore a file, the media manager handles the actions required to load, label, and unload the correct tape.
The media management interface is also called the media management layer, the media management library (MML), and the SBT interface.
See Also: media manager
The application of online or archived redo records to a restored backup to bring it current to a specified time. When performing media recovery, you can recover:
If you use all redo data, you perform complete recovery; if you use only part of the redo data, you perform incomplete recovery. Typically, you perform media recovery after a media failure.
In ARCHIVELOG mode, you have the choice of complete or incomplete recovery. In NOARCHIVELOG mode, your only option is typically to restore from the most recent backup without applying redo data.
In exceptional circumstances, you can recover a datafile or database if the database is not in ARCHIVELOG mode, but only if none of the online logs has been overwritten since the backup.
Using the O/S to maintain an identical copy of Oracle data. Typically, mirroring is performed on duplicate hard disks at the operating system level, so that if one of the disks becomes unavailable, the other disk can continue to service requests without interruptions. For example, you can mirror a datafile so that Oracle writes the same information to two different disk drives. You can then break the mirror to create a backup and later resilver the mirror.
When you mirror files, Oracle writes once while the operating system writes to multiple disks; when you multiplex files, Oracle writes the same data into multiple files.
An instance that is started and has the control files associated with the database open. You can mount a database without opening it; typically, you put the database in this state for maintenance or for restore and recovery operations.
See Also: instance
RMAN-generated incremental backups that allow you to conserve space by planning which blocks you want to back up and when. A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data. When you generate a level n incremental backup in which n is greater than 0, you back up either:
You can create a backup strategy in which you generate a backup at a different level each day, thereby controlling how much data you back up.
The automated maintenance of more than one identical copy of the online redo log. To multiplex the online logs, create multiple members in each redo log group. The degree of multiplexing is directly related to the number of members in each group.
The automated maintenance of more than one identical copy of a database's control file. To multiplex the control file, create multiple entries in the CONTROL_FILES initialization parameter.
Datafile blocks included in the same RMAN backup set are multiplexed, i.e., mixed together. Blocks from all datafiles in the backup set are interspersed with blocks from the other datafiles in the set.
The Oracle process ARCn is able to archive multiple copies of a redo log. You can multiplex archived redo logs by setting LOG_ARCHIVE_DEST_n (where n is an integer from 1 to 5, allowing up to four extra copies) or LOG_ARCHIVE_DUPLEX_DEST (allowing one extra copy) in your INIT.ORA file.
See Also: mirroring
Using multiple ARCn processes to archive online redo logs to one or more locations. Multiple ARCn processing prevents the bottleneck that occurs when LGWR writes to the online redo log faster than a single archive process can write to the archive destination(s). You can enable this feature at startup or at runtime by setting the initialization parameter LOG_ARCHIVE_MAX_PROCESS = n, where n is any integer from 1 to 10.
The mode of the database in which Oracle does not require filled online redo logs to be archived to disk. Specify the mode at database creation or change it by using the ALTER DATABASE command. Oracle does not recommend running in NOARCHIVELOG mode because it severely limits the possibilities for recovery of lost data.
The transmittal of archived redo log files to a local disk.
See Also: standby transmission
A tablespace that is not available to users when the database is open. You can only take a tablespace offline while the database is open. If a tablespace is taken offline, all online datafiles contained in the tablespace are taken offline.
You can take a tablespace offline using the ALTER TABLESPACE OFFLINE statement with three different options:
All the files in the tablespace are checkpointed, then taken offline. This option is sometimes called offline clean. If any datafile belonging to the tablespace is not available, the tablespace cannot be taken offline normal. Datafiles in a tablespace taken offline cleanly do not need to be recovered before the tablespace is brought back online.
All datafiles in the tablespace that are accessible to Oracle are checkpointed, then taken offline. Files that were checkpointed by the OFFLINE TEMPORARY command do not need recovery. Datafiles that were not checkpointed because they were not accessible at the time of an OFFLINE IMMEDIATE command must be recovered before the tablespace is brought back online.
All files in the tablespace are taken offline without any attempt to checkpoint the files first. All files in the tablespace must be recovered before the tablespace is brought online.
See Also: offline datafile
A datafile that is not available to users when the database is open. In exceptional circumstances, Oracle will automatically take a datafile offline if required. This file will need recovery before it can be brought online.
You can take a datafile offline either:
See Also: offline tablespace
A datafile that users can access. The database can be open or mounted when you issue the command ALTER DATABASE DATAFILE filename ONLINE. If the database is open, the datafile must be consistent with the rest of the database before you can bring it online. If the database is mounted, then you can bring the datafile online without being consistent with the other datafiles, but it will require recovery before the database is opened.
See Also: online tablespace
The online redo log is a set of two or more files that record all changes made to Oracle datafiles and control files. Whenever a change is made to the database, Oracle generates a redo record in the redo buffer. The LGWR process flushes the contents of the redo buffer into the online redo log.
The current online redo log is the one being written to by LGWR. When LGWR gets to the end of the file, is performs a log switch and begins writing to a new log file. If you run the database in ARCHIVELOG mode, then the ARCn process or processes copy the redo data into an archived redo log.
See Also: archived redo log
A tablespace that is available to users while the database is open. You can make a tablespace available for access by users by issuing the command ALTER TABLESPACE tablespace_name ONLINE. The database must be open to alter a tablespace online, and all files in the tablespace must be consistent with the rest of the database before the tablespace can be made online.
See Also: online datafile
A backup of one or more datafiles taken while a database is open. When you make an O/S backup while the database is open, you must put the tablespaces in hot backup mode by issuing an ALTER TABLESPACE BEGIN BACKUP command. When you make a backup using Recovery Manager while the database is open, however, you do not need to put the tablespaces in hot backup mode.
See Also: hot backup mode
A database that is available to users to query and update. The database is opened either automatically through a STARTUP statement or explicitly through an ALTER DATABASE OPEN statement.
Backups and copies that are unusable because they belong to incarnations of the database that are not direct ancestors of the current incarnation. For a visual depiction of orphaned backups, see "Reporting on Orphaned Backups".
A form of recovery in which several processes simultaneously apply changes from redo log files. Instance and media recovery can be parallelized automatically by specifying an initialization parameter or options to the SQL/SQL*Plus RECOVER command. Oracle uses one process to read the log files sequentially and dispatch redo information to several recovery processes, which apply the changes from the log files to the datafiles.
See Also: serial recovery
Allocating multiple channels for Recovery Manager backup and recovery operations. You can parallelize:
A file created by the ORAPWD command. A database must use password files if you wish to connect as SYSDBA over a network. For a more comprehensive explanation, see the Oracle8i Administrator's Guide.
Physical database files that have been copied from one place to another. The files can be datafiles, archived redo logs, or control files. You can make physical backups using Recovery Manager or with O/S commands such as the UNIX dd.
The datafiles, tablespaces, redo threads, and redo logs that exist in a database at a given time. Issue the RMAN report schema command to obtain a list of tablespaces and datafiles.
A full resynchronization of the recovery catalog updates all changed RMAN metadata, including physical schema information. If the database is open, RMAN also gathers information about rollback segments. A partial resynchronization of the recovery catalog does not update physical schema or rollback information.
See Also: resynchronization
The functionality that enables a media manager to take over the transfer of data between the media storage device and disk during RMAN backup and restore operations.
See Also: media manager
A database opened with the ALTER DATABASE OPEN READ ONLY command. As their name suggests, read-only databases are for queries only and cannot be modified. Oracle allows a standby database to be run in read-only mode, which means that it can be queried while still serving as an up-to-date emergency replacement for the primary database.
A tablespace whose status has been changed to prevent it from being updated. You put in read-only mode by executing the SQL statement ALTER TABLESPACE <tablespace> READ ONLY. Typically, you put a tablespace in read-only mode to reduce the frequency with which it is backed up. For example, instead of backing up the tablespace nightly, you reduce the backup frequency to once a month.
(1) A Recovery Manager command that updates a restored datafile by the application of incremental backups (if they exist) and then by the application of archived or online redo logs.
(2) A SQL*Plus command that updates a restored file by the application of archived or online redo logs.
See Also: recovery
The application of redo data or incremental backups to database files in order to reconstruct lost changes. The three types of recovery are instance recovery, crash recovery, and media recovery. Oracle performs the first two types of recovery automatically using online redo records; only media recovery requires you to restore a backup and issue commands. Only Recovery Manager allows you to recover datafiles by applying incremental backups.
A set of Oracle tables and views used by Recovery Manager to store information about Oracle databases. Recovery Manager uses this data to manage the backup, restore, and recovery of Oracle databases. If you choose not to use a recovery catalog, RMAN uses the target database control file.
See Also: recovery catalog database
An Oracle database that contains a recovery catalog schema. You should not store the recovery catalog in your target database.
A utility that backs up, restores, and recovers Oracle databases. You can use it with or without the central information repository called a recovery catalog. If you do not use a recovery catalog, RMAN uses the database's control file to store information necessary for backup and recovery operations. You can use RMAN in conjunction with a media manager, which allows you to back up files to tertiary storage.
One or more tablespaces that are being recovered to an earlier point in time during TSPITR. After TSPITR, all database objects in the recovery set have been recovered to
A file containing redo records. There are two types of redo logs: online redo logs and archived redo logs.
The online redo log is a set of two or more files that records all changes made to Oracle datafiles and control files. The LGWR process records the redo records in the log. The current online redo log is the one LGWR is currently writing to.
The archived redo log, also known as the offline redo log, is a copy of the online redo log that has been copied to an offline destination. If the database is in ARCHIVELOG mode, the ARCn process or processes copy each online redo log to one or more archive log destinations after it is filled.
The memory buffer in the system global area (SGA) in which Oracle logs redo records. The background process LGWR flushes the buffers into the current online redo log.
See Also: redo record
Each online redo log belongs to a group. A group has one or more identical members. A multiplexed redo log is a redo log in which the redo groups have multiple members.
A group of change vectors describing a single, atomic change to the database. Oracle constructs redo records for all data block changes and saves them on disk in the current online redo log. Redo records allow changes to database blocks to be reconstructed should data loss occur.
See Also: redo log
In RMAN, the execution of a register database command in order to record the existence of a target database in the recovery catalog.
A method for opening a database that results in a new database incarnation, the resetting of the log sequence number to 1, and the re-formatting or re-creation of the online redo logs. A database must be opened with the RESETLOGS keyword after:
Informing the operating system or hardware managing the mirror that you want to refresh a broken mirror from the half that is up-to-date and then maintain both sides of the mirror.
The replacement of a lost or damaged file with a backup. You can restore files either with O/S commands such as UNIX cp or the RMAN restore command.
See Also: recover
The operation that updates the recovery catalog with current information from the target database control file. You can initiate a full resynchronization of the catalog by issuing a resync catalog command.
Partial resynchronizations transfer information to the recovery catalog about archived redo logs, backup sets and datafile copies. Partial resynchronizations will not transfer information such as:
If Recovery Manager determines that a full or partial resynchronization is necessary, it initiates one automatically before commands such as backup, copy, restore, and recover.
The use of rollback segments to undo uncommitted transactions applied to the database during the rolling forward stage of recovery.
The application of redo records or incremental backups to datafiles and control files in order to recover changes to those files.
System Backup to Tape
See Also: media management interface
A form of recovery in which a single process applies the changes in the redo log files sequentially.
See Also: parallel recovery
A group of shared memory structures that contain data and control information for one Oracle database instance. The SGA and Oracle processes constitute an Oracle instance. Oracle automatically allocates memory for an SGA whenever you start an instance and the operating system reclaims the memory when you shut down the instance. Each instance has one and only one SGA.
A copy of a database's control file taken by Recovery Manager. RMAN uses the snapshot control file to read a consistent version of a control file when either resynchronizing the recovery catalog or backing up the control file. A snapshot control file is created by Recovery Manager using the same Oracle code that creates backup control files: ALTER DATABASE BACKUP CONTROL FILE TO 'location'.
See fractured block
The process of restoring archived logs from tertiary storage to disk in order to allow recovery to proceed. RMAN stages the logs to disk when the recover command is executed. To use this feature, you must configure a media manager.
See Also: media manager
RMAN commands that you do not have to execute within the brackets of a run command.
See Also: job commands
An identical copy of a production database that you can use for disaster protection. You can update your standby database with archived redo logs from the production database in order to keep it current. Should a disaster destroy the production database, you can activate your standby database and make it the new production database.
The transmittal of archived redo log files via a network to either a local or remote standby database.
See Also: standby database
A sequence of RMAN commands stored in the recovery catalog.
See Also: recovery catalog
A Recovery Manager command which converts a datafile copy into a datafile used by an Oracle database. It performs the equivalent function of the SQL statement ALTER DATABASE RENAME FILE 'original_name' TO 'new_name', and also marks the datafile copy as no longer available.
A stamp that defines a committed version of a database at a point in time. Oracle assigns every committed transaction a unique SCN.
A database is divided into one or more logical storage units called tablespaces. Each tablespace has one or more physical datafiles exclusively associated with it.
See Also: datafile
The recovery of one or more non-SYSTEM tablespaces to a point in time that is different from the database. You can use either RMAN or O/S methods to perform TSPITR.
A user-specified character string that acts as a symbolic name for a backup set or image copy. You can specify a tag when executing the restore or change command. The maximum length of a tag is 30 characters.
The most recent redo record in the redo log file. As users make changes to the database, the tail keeps moving forward. Since the latest checkpoint is always temporally behind the tail of the log, it is said to lag the tail of the log. If the checkpoint lags the tail of the log significantly, recovery time increases.
Writing output to a tape drive fast enough to keep the tape constantly busy.
A piece of hardware that reads and writes magnetic tapes.
One physical piece of tape media.
In RMAN, the database that you are backing up or restoring.
Each Oracle instance has its own set of online redo log groups. These groups are called a thread of online redo. In non-OPS environments, each database has only one thread that belongs to the instance accessing it. In OPS environments, each instance has a separate thread, i.e., each instance has its own online redo log. Each thread has its own current log member.
The incomplete recovery of database files to a non-current time. Time-based recovery is also known as point-in-time recovery. There are two types:
A feature that allows you to transport a set of tablespaces from one database to another. Transporting or "plugging" a tablespace into a database is like creating a tablespace with pre-loaded data. This feature is often an advantage because:
A test that checks whether a backup set or copy can be restored. RMAN scans all of the copies or backup pieces in the specified backup sets and looks at the checksums to verify that the contents can be successfully restored.
Use the restore ... validate or validate backupset command when you suspect that one or more copies or backup pieces in a backup set are missing or have been damaged. Note that restore ... validate and validate backupset actually test whether the files can be restored, whereas change ... crosscheck and crosscheck merely examine the file headers.
A backup of the control file and all datafiles that belong to a database.
See Also: backup