What is database recovery?
Introduction to Database Recovery A major responsibility of the database administrator is to prepare for the possibility of hardware, software, network, process, or system failure. If such a failure affects the operation of a database system, you must usually recover the database and return to normal operation as quickly as possible.
How to recover data files after a system failure?
These changes were either saved to the datafiles before the failure, or introduced during the roll forward phase. 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 segments (transaction recovery).
What are the structures used for database recovery?
Structures Used for Database Recovery Rolling Forward and Rolling Back Improving Recovery Performance Recovery Manager Database Archiving Modes Control Files Database Backups Survivability See Also: Oracle8i Recovery Manager User's Guide and Referencefor the procedures to create and maintain backup and recovery structures
How to recover a SQL Server database from a failure?
To recover a SQL Server database from a failure, a database administrator has to restore a set of SQL Server backups in a logically correct and meaningful restore sequence. SQL Server restore and recovery supports restoring data from backups of a whole database, a data file, or a data page, as follows: The database (a complete database restore)
What are the types of database recovery?
What Are the Types of Recovery? There are three basic types of recovery: instance recovery, crash recovery, and media recovery.
What is database recovery failure?
13.2. Database Recovery Concepts The failure may be the result of a system crash due to hardware or software errors, a media failure such as head crash, or a software error in the application such as a logical error in the program that is accessing the database.
How can you recover a database crash?
There are two major techniques for recovery from non-catastrophic transaction failures: deferred updates and immediate updates. Immediate update – In the immediate update, the database may be updated by some operations of a transaction before the transaction reaches its commit point.
What is database recovery in database?
Recovery is the rebuilding of a database or table space after a problem such as media or storage failure, power interruption, or application failure. If you have backed up your database, or individual table spaces, you can rebuild them should they become damaged or corrupted in some way.
What is log file in DBMS?
DBMSDatabaseBig Data Analytics. Log is nothing but a file which contains a sequence of records, each log record refers to a write operation. All the log records are recorded step by step in the log file. We can say, log files store the history of all updates activities.
What does database recovery require?
If such a failure affects the operation of a database system, you must usually recover the database and return to normal operation as quickly as possible. Recovery should protect the database and associated users from unnecessary problems and avoid or reduce the possibility of having to duplicate work manually.
How does a recovery manager recover from a failure?
Recovery manager initiates recovery from the transaction logs. Transactions which are in active list and failed list are undone and written on the abort list. Transactions which are in before-commit list are redone. No action is taken for transactions in commit or abort lists.
What is the recovery scheme for a failed transaction?
In this scheme, the recovery scheme depends greatly on the concurrency control scheme that is used. So, to rollback a failed transaction, we must undo the updates performed by the transaction. Transaction rollback : In this scheme, we rollback a failed transaction by using the log.
What happens when you type recover database?
After performing closed database recovery, the database is recovered up to the moment that media failure occurred. You can then open the database using the SQL command ALTER DATABASE with the OPEN option. See Also: For more information about applying redo log files, see "Applying Redo Log Files".
What is database backup and recovery?
Backup and recovery describes the process of creating and storing copies of data that can be used to protect organizations against data loss. This is sometimes referred to as operational recovery.
What is database recovery Management in DBMS?
Database recovery management or recovery system in DBMS help to recover the failure. Types of Failures in DBMS. Different types of Failure in DBMS are as follow – Hardware Failures. Include memory errors, disk problems, crashes, bad sectors, etc.
What is database recovery in SQL?
SQL Server restore and recovery supports restoring data from backups of a whole database, a data file, or a data page, as follows: The database (a complete database restore) The whole database is restored and recovered, and the database is offline for the duration of the restore and recovery operations.
What happens if Oracle fails to execute a statement?
If a statement failure occurs, the Oracle software or operating system returns an error code or message. A statement failure usually requires no action or recovery steps; Oracle automatically corrects for statement failure by rolling back the effects (if any) of the statement and returning control to the application.
What is process failure?
A process failure is a failure in a user, server, or background process of a database instance such as an abnormal disconnect or process termination. When a process failure occurs, the failed subordinate process cannot continue work, although the other processes of the database instance can continue.
What is the responsibility of a database administrator?
A major responsibility of the database administrator is to prepare for the possibility of hardware, software, network, process, or system failure. If such a failure affects the operation of a database system, you must usually recover the database and return to normal operation as quickly as possible. Recovery should protect the database and ...
Why is recovery important?
Recovery should protect the database and associated users from unnecessary problems and avoid or reduce the possibility of having to duplicate work manually. Recovery processes vary depending on the type of failure that occurred, the structures affected, and the type of recovery that you perform.
What happens if a transaction fails before reaching its commit point?
If a transaction fails before reaching its commit point, it will not have changed the database in any way so UNDO is not needed. It may be necessary to REDO the effect of the operations that are recorded in the local transaction workspace, because their effect may not yet have been written in the database.
How to backup a database?
Some of the backup techniques are as follows : 1 Full database backup – In this full database including data and database, Meta information needed to restore the whole database, including full-text catalogs are backed up in a predefined time series. 2 Differential backup – It stores only the data changes that have occurred since last full database backup. When same data has changed many times since last full database backup, a differential backup stores the most recent version of changed data. For this first, we need to restore a full database backup. 3 Transaction log backup – In this, all events that have occurred in the database, like a record of every single statement executed is backed up. It is the backup of transaction log entries and contains all transaction that had happened to the database. Through this, the database can be recovered to a specific point in time. It is even possible to perform a backup from a transaction log if the data files are destroyed and not even a single committed transaction is lost.
What is the log file used for recovery?
Recovery techniques are heavily dependent upon the existence of a special file known as a system log. It contains information about the start and end of each transaction and any updates which occur in the transaction. The log keeps track of all transaction operations that affect the values of database items.
Error: SQL Server restore failed because the database is in use
When you use T-SQL or SSMS to restore SQL databases, sometimes an error may occur saying “Exclusive access could not be obtained because the database is in use” and the problematic database will be followed by a "restoring..." mark, which blocks you from any normal operation on it.
Way 1. Close existing connections to destination database
If you prefer to use SSMS GUI, try ticking one more option in Restore Database window to close all the existing connections to the target database.
Way 2. Switch SQL Server to single user mode
Since the SQL Server restore may fail because the database is used by other users, you can switch SQL Server to single user mode, and then set it to multi user mode again. This will close all the active connections as well.
Way 3. Restore SQL Server database with recovery
There’s another simple tip that works for me, i.e. restore the problematic database WITH RECOVERY.
Way 4. Change the default database back to master
The SQL Server database restoring issue is sometimes due to your login using the target database as its default database, which will always keep a connection session alive. To fix it, you need to change the default database back to “master”.
Way 5. Restart the SQL Server service thoroughly
This one is more of a final resort. If all other methods failed, then you can try restarting SQL service thoroughly.
Way 6. Alternative to restore SQL database without error
The database in use error is not rare in SQL Server recovery. In my case, it often appears when I restore multiple databases using T-SQL commands, and it’s really troublesome to repair them one by one each time. Therefore, I prefer to manage SQL database backup and restore with error-free alternative like AOMEI Centralized Backupper Database.
