What happens when we give alter database begin backup?
When we execute the SQL command “ALTER DATABASE BEGIN BACKUP,” several key actions are initiated within the database management system (DBMS). This command is used to prepare a database for a backup operation, ensuring that all subsequent changes to the database are captured in the backup. Understanding the sequence of events triggered by this command is crucial for maintaining data integrity and efficient backup processes. Let’s delve into the details of what happens when we give alter database begin backup.
The first action that occurs when the “ALTER DATABASE BEGIN BACKUP” command is executed is the locking of the database. The DBMS ensures that no other user or process can make any changes to the database until the backup operation is complete. This locking mechanism prevents any inconsistencies or data corruption that might arise from concurrent modifications.
Once the database is locked, the DBMS starts tracking all the changes made to the database in real-time. This process is known as transaction logging. The DBMS records every transaction, including inserts, updates, and deletes, in a log file. These log files are crucial for recovering the database in case of a failure or data loss.
The next step is to prepare the backup files. The DBMS allocates space for the backup files and initializes them. The backup files are typically stored on a separate storage device, such as a tape drive or a disk array, to ensure that they are not affected by any hardware failures.
After the backup files are prepared, the DBMS starts copying the data from the database to the backup files. This process involves reading the data pages from the database and writing them to the backup files. The DBMS ensures that all the data is consistent and up-to-date by copying the data pages that were modified after the “ALTER DATABASE BEGIN BACKUP” command was executed.
Once the data is copied to the backup files, the DBMS performs a consistency check to ensure that the backup files are error-free. This check involves verifying the integrity of the data pages and the log files. If any errors are detected, the DBMS may abort the backup operation and raise an error message.
Finally, once the backup operation is complete, the DBMS releases the lock on the database, allowing other users and processes to make changes to the database again. The backup files are now ready for use, and can be restored to the database in case of a failure or data loss.
In summary, when we give the “ALTER DATABASE BEGIN BACKUP” command, the DBMS locks the database, tracks changes in real-time through transaction logging, prepares backup files, copies the data to the backup files, performs a consistency check, and finally releases the lock on the database. Understanding this sequence of events is essential for ensuring the success and reliability of backup operations in a database environment.
