Basic knowledge of Oracle Database Backup

The following articles mainly introduce the basic knowledge of Oracle Database Backup, including the structure used in the actual operation of Oracle Database Backup and the content of online logs, and role management for archiving logs and Oracle databases.

I. structure used for Oracle Database Backup 

Oracle databases use several structures to protect data: database backup, logs, rollback segments, and control files.

1. Database Backup is composed of the operating system backup that makes up the physical files of the Oracle database. When a media fault occurs, the database is restored and the destroyed data files or control files are recovered using backup files.

2. Each Oracle database instance provides logs to record all modifications made in the database. Each running Oracle database instance has an online log, which works with the Oracle background process LGWR and immediately records all modifications made to the instance. Offline archiving) logs are optional. Once an Oracle database instance is filled with online logs, an online log archive file can be formed. Archived online log files are uniquely identified and merged into archived logs.

3. the rollback segment is used to store the old value of the modified value of an ongoing transaction as an uncommitted transaction. This information is used to cancel any uncommitted modification during database recovery.

4. control files are generally used to store the status of the physical structure of the database. Some status information in the control file is used to guide Oracle during instance recovery and media recovery.

Ii. Online logs

Each instance of an Oracle database has an associated online log. An online log consists of multiple online log files. Online log file (online redo log file) is filled with the log item redo entry). The data recorded in the log item is used to reconstruct all modifications made to the database.

Iii. Archiving logs

When Oracle wants to archive a full online log File Group, archive logs must be created ). It is useful for Oracle database backup and recovery:

1. database backup and online and archive log files Ensure that all submitted items can be recovered in the case of operating system and disk faults.

2. When the database is opened and used normally, if the archived logs are permanently saved, they can be used online backup.

Databases can run in NOARCHIVELOG or ARCHIVELOG modes. When a database is used in NOARCHIVELOG mode, online logs cannot be archived. If the database runs in ARCHIVELOG mode, you can archive online logs.

Iv. Oracle backup features

Oracle backup includes logical backup and physical backup.

1. Logical backup

The logical backup of the database contains reading a database record set and writing the record set to a file.

1) Output Export) the output can be the entire database, specified user, or specified table.

2) Input Import) the input will read the binary dump file created by the output and execute its command.

2. Physical backup

Physical backup includes copying the files that constitute the database regardless of the logical content.

Oracle supports two different types of physical file backup: offline backup (offline backup) and online backup (online backup ).

1) offline backup is used to back up the following files when the database is normally closed and the database is in the "offline" state:

All data files

All control files

All online logs

Init. ora (optional)

2) online backup

Online backup can be used to back up any databases that operate in the ARCHIVELOG mode. In this way, online logs are archived and a complete record of all jobs is created in the database.

The online backup process has powerful functions. First, a full point-in-time recovery is provided. Second, the database is allowed to be enabled during file system backup.

Backup Mode features comparison

Method Type recovery features

The Export logic can restore any database object to the output state.

Offline Backups can physically restore the database to the closed state: if the database runs in ARCHIVELOG mode, it can be restored to any time point.

Online Backups physical recovery of databases to any point in time

V. role management of Oracle databases

The basic measures taken by the Oracle database system to manage database security using roles include:

The user name and password are verified to prevent non-Oracle users from registering with the Oracle database and performing illegal access to the database.

Grant the user certain permissions to restrict the user's permission to manipulate the database.

Grant users the permission to access and execute database entities to prevent users from accessing unauthorized data.

Provides an Oracle database Entity Access audit mechanism so that the database administrator can monitor the data access and system resource usage in the database.

The view mechanism is used to restrict access to the row and column sets of the base table.