18.1 data guard Overview

Data guard is a solution provided by Oracle to ensure high availability, data protection, and disaster recovery of enterprise data.

1. Data guard configuration

Data guard consists of a product database and one or more slave databases, which can be distributed to different locations and regions. The interconnection between these databases is achieved through Oracle Net. When configuring data guard, you must include the primary database and at least one standby database ).

(1) primary database. A primary database is an Oracle database used to store Application System data. It is also called a product database or a target database.

(2) backup database. The standby database is a consistent copy of the primary database, which includes two types: Physical standby database and logical standby database. A backup database is a database created using primary database backup. Each primary database can have up to nine backup databases.

2. Physical backup database

The physical standby database has the same physical copy as the primary database. By applying the redo data of the primary database, the physical standby database is synchronized with the primary database. When a transaction changes in the primary database, Oracle writes the redo data to the redo log and archive log. After the archived logs are transmitted to the host where the physical standby database is located, the physical standby database can directly apply these transaction changes to maintain synchronization with the primary database.

3. Logical backup database

The logical standby database has the same logical information as the product database. Note that the physical standby database has the same physical structure as the primary database, while the physical structure of the logical standby database can be different from that of the primary database. When a transaction changes in the primary database, Oracle writes the redo data to the redo log and archive log. After the archived logs are transmitted to the host where the logical standby database is located, Oracle converts the redo data to the corresponding SQL statement and finally executes the SQL statement on the logical standby database, in this way, the synchronization between the logical standby database and the primary database is maintained.

4. Advantages of physical standby Databases

• The physical backup database provides robust and effective disaster recovery and high availability solutions. When the primary database fails due to unforeseen faults, the Standby database can be immediately converted to the primary database, reducing the downtime of the primary database.
• The physical standby database provides high-level data protection and security measures. By using the maximum protection mode of data guard, the transaction changes of the primary database are synchronized to the physical standby database. In this way, when the primary database fails due to unforeseen faults, no data will be lost.
• Reduces the workload of the primary database. The physical standby database can be opened in read-only mode. If the primary database has a large load, you can transfer data statistics, data reports, query execution, and other operations to the physical standby database, this saves the CPU and I/O costs of the primary database.

5. Prerequisites for the physical backup database

1. Mandatory log features of the primary database must be activated
2. The primary database must be in archivelog mode.