Block media recovery is a technique for restoring and recovering individual data blocks while all database files remain online and available. A disk limit lets you use the remaining disk space for other purposes and not to dedicate a complete disk for the flash recovery area. The recovery is performed automatically by a surviving instance in the configuration. You cannot perform complete recovery because an archived redo log is missing. There could be other data relationships that are not declared with database constraints. You can make online backups only if your database is running in ARCHIVELOG mode. The reconstructing of data is achieved through media recovery, which refers to the various operations involved in restoring, rolling forward, and rolling back a backup of database files. See the section Setting Up a Flash Recovery Area for RMAN in chapter Setting Up and Configuring Backup and Recovery in Oracle Database Backup and Recovery Basics 10g Release 1 (10.1). Backups are divided into physical backups and logical backups. Configure the location of the snapshot control file using the instructions given in section Configuring the RMAN Snapshot Control File Location in chapter Configuring Recovery Manager and Archiving in Oracle Real Application Clusters Administrator's Guide 10g Release 1 (10.1). The interface to block media recovery is provided by RMAN. In other words, you must still run recovery even though the archived logs are not needed. With these files, you can perform a complete recovery. Media recovery involves various operations to restore, roll forward, and roll back a backup of database files. For Flashback Table to succeed, the system must retain enough undo information to satisfy the specified SCN or timestamp, and the integrity constraints specified on the tables cannot be violated. If the flash recovery area is big enough to keep a copy of the tablespaces, then those tablespaces do not need to access tertiary storage. The sections that follow describe how to backup a single-instance Oracle 10g database. Has a recovery time governed solely by user policy (for example, frequency of backups, parallel recovery parameters, number of database transactions since the last backup) rather than by Oracle internal mechanisms. Because you are not completely recovering the database to the most current time, you must tell Oracle when to terminate recovery. The database should be configured to use the Flash Recovery Area. The RESETLOGS operation creates a new incarnation of the databasein other words, a database with a new stream of log sequence numbers starting with log sequence 1. Following is a list of recovery-related files in flash recovery area: Oracle lets you define a disk limit, which is the amount of space that Oracle can use in the flash recovery area. whether the changes are committed or uncommitted. During normal database operation, Oracle occasionally logs these block images in Flashback logs. Because rollback data is also recorded in the redo log, rolling forward also regenerates the corresponding rollback segments. This makes it possible to perform on-line backups of the database.

The sections that follow provide more details. Flashback Table does not address physical corruption; for example, bad disks or data segment and index inconsistencies. Both datafile media recovery and instance recovery must repair database integrity. Do not restart the servers until the procedure has been performed. The sections that follow provide more details about these procedures. Datafile backups, which are not as common as tablespace backups, are valid in ARCHIVELOG databases. It will be used to store most of the backup and recovery-related files. This method, also called user-managed backup and recovery, is fully supported by Oracle, although use of RMAN is highly recommended because it is more robust and greatly simplifies administration. You lose your current control file and must use a backup control file to open the database. This can happen due to application error or user error, such as accidentally deleting a table or tablespace. Before using the OPEN RESETLOGS command to open the database in read/write mode after an incomplete recovery, it is a good idea to first open the database in read-only mode, and inspect the data to make sure that the database was recovered to the correct point. Flashback Table cannot be used on a standby database. To solve this dilemma, two separate steps are generally used by Oracle for a successful recovery of a system failure: rolling forward with the redo log (cache recovery) and rolling back with the rollback or undo segments (transaction recovery). Import, or Data Pump Import, reads export files and restores the corresponding data into an existing database. This means that the files in the backup contain all the data taken from a same point in time. The exact tool and procedure you use depends on the type of database you have created (InnoDB, MyISAM, ISAM). The main difference is that Oracle manages the undo for you. However, Flashback is preferable to using the RESTORE and RECOVER commands in some cases, because it is faster and easier, and does not require restoring the whole database. If you lose the original data, then you can reconstruct it by using a backup. When this type of backup is restored and archived logs are available, you have the option of either opening the database immediately and losing transactions that were made since the backup was taken, or applying the archived logs to recover those transactions. To correct problems caused by logical data corruptions or user errors, you can use Oracle Flashback. A user error affected a table or a small set of tables, but the impact of reverting this set of tables is not clear because of the logical relationships between tables. The block is a fractured block, meaning that the data in this block is not consistent. Use Flashback Table with Oracle Flashback Version query and Flashback Transaction Query to find a time to which the table should be restored back to. Figure 15-2 illustrates the basic principle of backing up, restoring, and performing media recovery on a database. You have a choice between two basic methods for recovering physical files. You can consider this staggered backup as a whole database backup. A backup is a safeguard against unexpected data loss and application errors. Oracle Database Backup and Recovery User's Guide for information about performing backups of multitenant container databases (CDBs) and pluggable databases (PDBs). You should follow these basic steps: After identifying which files are damaged, place the database in the appropriate state for restore and recovery. Whether you use RMAN or user-managed methods, you can supplement your physical backups with logical backups of schema objects made using the Export utility. Configure the RMAN Control file Autobackup feature according to section Configuring the RMAN Control File Autobackup Feature in chapter Configuring Recovery Manager and Archiving in Oracle Real Application Clusters Administrator's Guide 10g Release 1 (10.1). This chapter contains the following topics: "Overview of Database Backup and Recovery Features", Oracle Database Backup and Recovery Basics, Oracle Database Backup and Recovery Advanced User's Guide. You can also restore backup sets containing archived redo logs, but this is usually unnecessary, because RMAN automatically restores the archived logs that are needed for recovery and deletes them after the recovery is finished. You can make physical backups with either the Recovery Manager (RMAN) utility or operating system utilities. A consistent backup is one in which the files being backed up contain all changes up to the same system change number (SCN). Recovers the data up to a specified point in time. The procedures for backing up the slee_db database are specific to the type of database you have deployed: a MySQL system is backed up differently than an Oracle 10g system. Oracle utilities are used to move Oracle schema objects in and out of Oracle. Oracle creates archived logs in the flash recovery area. For a primary database, consider using Flashback Database rather than Flashback Table in the following situations: There is a logical data corruption, particularly undo corruption. Oracle automatically creates, deletes, and resizes Flashback logs in the flash recovery area. You can perform the following types of media recovery. When some but not all instances of an Oracle Real Application Clusters configuration fail (instance recovery). Undo blocks (whether in rollback segments or automatic undo tablespaces) record database actions that should be undone during certain database operations. The RMAN configuration option, CONTROLFILE AUTOBACKUP, should be set to ON. If you do not already use RMAN as your principal backup and recovery solution, then you can still perform block media recovery by cataloging into the RMAN repository the necessary user-managed datafile and archived redo log backups. After rolling forward, the data blocks contain all committed changes. It requires configuration and resources, but it provides a fast alternative to performing incomplete database recovery. Rolling forward usually includes online redo log files (instance recovery or media recovery) and could include archived redo log files (media recovery only). Also, you can tune the rolling forward and rolling back phases of instance recovery separately. To perform a whole database backup when the database is open: Connect RMAN to the target database as described in "Connecting to the Target Database Using RMAN. A tablespace backup is a backup of the datafiles that constitute the tablespace. If you are performing complete recovery on a tablespace or datafile, then you must: Take the tablespace or datafile to be recovered offline if the database is open, Restore a backup of the datafiles you want to recover. In contrast, instance recovery is the recovery of one failed instance by a live instance in an Oracle Real Application Clusters configuration. In other words, some changes are missing. A backup of online datafiles is called an online backup. This process is called rolling back or transaction recovery. To make an efficient backup, the database must: In addition, the RMAN option CONTROLFILE AUTOBACKUP should be set to ON. You can run Oracle in either manual undo management mode or automatic undo management mode. You cannot use it on the SYSTEM tablespace, an UNDO tablespace, or any tablespace that contains rollback segments. When to Use CREATE TABLE AS SELECT Recovery, When to Use Import/Export Utilities Recovery, When to Use Tablespace Point-in-Time Recovery. This section does not describe how to restore the Oracle software. Flashback Table works like a self-service repair tool.

Use Oracle RMAN to perform the backup. Although your RDBMS server software should maintain a replicated database for a production installation, BEA recommends backing up the full slee_db once daily, to an offline location. Oracle Database 10g automatically tunes a parameter called the undo retention period. While whole database backups can be an important element in your overall backup strategy, they are also a required step in some situations, such as when you enable or disable ARCHIVELOG mode (see "Configuring Recovery Settings"). Scripting on this page enhances content navigation, but does not change the content in any way. The database cannot be opened if any of the online datafiles needs media recovery, nor can a datafile that needs media recovery be brought online until media recovery is complete. The slee_db also stores the alarm configuration and generated alarms. Media recovery could find nothing to do and signal the "no recovery required" error if invoked for files that do not need recovery. However, you can set parameters in the database server that can tune the duration of instance and crash recovery performance. After the roll forward phase, the datafiles could contain changes that had not been committed at the time of the failure. In this case, restore the files to their original location (for example, /usr/local/mysql/data) before restarting the server. Crash and instance recovery involve two distinct operations: rolling forward the current, online datafiles by applying both committed and uncommitted transactions contained in online redo records, and then rolling back changes made in uncommitted transactions to their original state. The undo retention period indicates the amount of time that must pass before old undo informationthat is, undo information for committed transactionscan be overwritten. Oracle recovers the redo threads of the terminated instances together. In database recovery, the undo blocks roll back the effects of uncommitted transactions previously applied by the rolling forward phase. The flash recovery area is an Oracle-managed directory, file system, or Automatic Storage Management disk group that provides a centralized disk location for backup and recovery files. Media recovery has the following characteristics: Applies changes to restored backups of damaged datafiles. RMAN uses a default format while naming the backup sets that comprise the backup. Before performing whole database backups, however, be aware of the implications of backing up in ARCHIVELOG and NOARCHIVELOG modes. The reason is that redo is required to make the restored tablespace consistent with the other tablespaces in the database. Before restoring a MySQL database, shut down all Network tier server instances. Configure the archive redo log according to the following sections in the chapter Configuring Recovery Manager and Archiving in Oracle Real Application Clusters Administrator's Guide 10g Release 1 (10.1): Configure the database to use a Flash Recovery Area. Typically, you perform complete media recovery after a media failure damages datafiles or the control file. If you are performing complete recovery on the whole database, then you must: Ensure that all datafiles you want to recover are online, Restore a backup of the whole database or the files you want to recover, Apply online or archived redo logs, or a combination of the two. For this reason, the instructions below provide only general guidelines for restoring a database. Unless the database is not open by any instance, datafile media recovery can only operate on offline datafiles. Typically, the term "media recovery" refers to recovery of datafiles. Oracle can roll back multiple transactions simultaneously as needed. Recovers until the specified log sequence number (only available when using Recovery Manager). Oracle Flashback Database and Oracle Flashback Table let you quickly recover to a previous time. Media recovery updates a backup to either to the current or to a specified prior time. Media recovery selectively applies the changes recorded in the online and archived redo logs to the restored datafile to roll it forward. ", Ensure that your database is in ARCHIVELOG mode as described in "Enabling Archiving of Redo Log Files.". Use RESTORE to restore datafiles from backup sets or from image copies on disk, either to their current location or to a new location. To backup the MySQL database, first prepare the database by: After preparing the database, use one of the available MySQL backup scripts, such as mysqldump or mysqlhotcopy, to create an offline copy of the database. A whole database backup is either a consistent backup or an inconsistent backup. A backup is a copy of data. A user error affected a table or a small set of tables, but using Flashback Table would fail because of its DDL restrictions. Flashback Database is not true media recovery, because it does not involve restoring physical files. The basic RMAN recovery commands are RESTORE and RECOVER. By definition, crash recovery is the recovery of a database in a single-instance configuration or an Oracle Real Application Clusters configuration in which all instances have crashed. Unlike an inconsistent backup, a consistent whole database backup does not require recovery after it is restored. Begin the restoration process by deleting any existing data files and reinstalling MySQL, if necessary. For example, the flash recovery area disk limit does not include the extra size of a file system that is compressed, mirrored, or some other redundancy mechanism. In NOARCHIVELOG mode, Oracle does not archive the redo logs, and so the required redo logs might not exist on disk. You can restore the table to the time before the deletion and see the missing rows in the table with the FLASHBACK TABLE statement. For example, assume that either RMAN or an operating system utility reads the block while database writer is in the middle of updating the block. You must use RMAN to restore a backup set. Figure 15-1 illustrates the valid configuration options given the type of backup that is performed. When updates are made to files in backup mode, additional redo data is logged. The bigger the flash recovery area, the more useful it becomes. Export, or Data Pump Export, writes data from an Oracle database to binary operating system files. You can make manual backups of the control file by using the following methods: The RMAN BACKUP CURRENT CONTROLFILE command makes a binary backup of the control file, as either a backup set or an image copy. The minimum size of the flash recovery area should be at least large enough to contain archive logs that have not been copied to tape. Read the instructions given in chapter Managing Backup and Recovery in Oracle Real Application Clusters Administrator's Guide 10g Release 1 (10.1). This view lists all files that require recovery and explains the error that necessitates recovery. Tablespace backups, whether online or offline, are valid only if the database is operating in ARCHIVELOG mode. This enables RMAN to make backups of the database Control File and Server Parameter File.

You can restore table data along with associated indexes, triggers, and constraints, while the database is online, undoing changes to only the specified tables. An inconsistent backup is a backup in which the files being backed up do not contain all the changes made at all the SCNs. Two potential problems can result if an instance failure occurs: Data blocks modified by a transaction might not be written to the datafiles at commit time and might only appear in the redo log. Therefore, the redo log contains changes that must be reapplied to the database during recovery. Oracle Flashback Database lets you quickly recover an Oracle database to a previous time to correct problems caused by logical data corruptions or user errors.

You can use the script to create a new control file. A user error causes data loss, for example, a user inadvertently drops a table. Follow the instructions given in section Instance Recovery in Real Application Clusters and section RMAN Backup Scenarios for Real Application Clusters in chapter Managing Backup and Recovery in Oracle Real Application Clusters Administrator's Guide 10g Release 1 (10.1). All changes to Oracle blocks are recorded in the online log. If you did not configure a default device, then the backup is created in the fast recovery area. The following sections describe how to backup and restore Oracle Communications Services Gatekeeper installations: In addition to the domain-level configuration backups described in Backing Up the Domain Configuration, you must backup the Oracle Communications Services Gatekeeper database (generally named slee_db). If you discover that too much recovery was done, then you must restore the database again and re-run the recovery. After an online backup or inconsistent closed backup, always ensure that you have the redo necessary to recover the backup by archiving the unarchived redo logs. In other words, you cannot recover from log 100 to log 200 if log 173 is missing. Before performing media recovery, you need to determine which datafiles to recover. Use the SQL*Plus RECOVER command to recover the datafile backups. Oracle can enforce this limitation when it detects data relationships that have been explicitly declared with database constraints. Oracle makes the control files and datafiles consistent to the same SCN during a database checkpoint. The only way to recover an inconsistent backup without archived logs is to use RMAN incremental backups. Because archived redo logs are essential to recovery, you should back them up regularly. Then, Oracle deletes the minimum set of existing files from the flash recovery area that are obsolete, redundant copies, or backed up to tertiary storage. You can use logical backups to supplement physical backups. Recovery Manager (RMAN) is an Oracle utility that can back up, restore, and recover database files. Suppose a user accidentally deletes some important rows from a table and wants to recover the deleted rows. However, these types of recovery differ with respect to their additional features. After the roll forward, any changes that were not committed must be undone. Instance recovery refers to the case where a surviving instance recovers a failed instance in an Oracle Real Application Clusters database. If you open the database read-only and discover that not enough recovery was done, then just run the recovery again to the desired time.

The utility writes data from an Oracle database to binary operating system files. Crash and instance recovery have the following shared characteristics: Redo the changes using the current online datafiles (as left on disk after the failure or SHUTDOWN ABORT), Use only the online redo logs and never require the use of the archived logs, Have a recovery time governed by the number of terminated instances, amount of redo generated in each terminated redo thread since the last checkpoint, and by user-configurable factors such as the number and size of redo log files, checkpoint frequency, and the parallel recovery setting.

For this reason, binary backups are preferable. The SQL statement ALTER DATABASE BACKUP CONTROLFILE TO TRACE exports the control file contents to a SQL script file. Because the autobackup uses a default filename, RMAN can restore this backup even if the RMAN repository is unavailable. Shut down the database and then mount the database using the following commands. The command is CONFIGURE CONTROLFILE AUTOBACKUP. You can: Use the RMAN utility to restore and recover the database, Restore backups by means of operating system utilities, and then recover by running the SQL*Plus RECOVER command. Incomplete recovery, or point-in-time recovery, uses a backup to produce a noncurrent version of the database. The database must be running in ARCHIVELOG Mode. If you do not have a backup, it is sometimes possible to perform recovery if you have the necessary redo logs dating from the time when the datafiles were first created and the control file contains the name of the damaged file. See the section Configuring Control File and Server Parameter File Autobackup in chapter Setting Up and Configuring Backup and Recovery in Oracle Database Backup and Recovery Basics 10g Release 1 (10.1). "Overview of Oracle Flashback Query" for information about Oracle Flashback Query, "Overview of Oracle Flashback Database" for information about reverting an entire database to an earlier point in time.