Oracle RAC and DG



RAC: real application clustersrac

RAC: real application clustersrac

Single node database: one to one correspondence between data files and sample files

When an instance is damaged, the database is corrupted

RAC architecture database: data files corresponding to multiple instances

The most fundamental intention of Rac is instance level fault tolerance, not data-based

Instances are all data based.

DataGuard is based on data fault tolerance.

Core technology of Oracle database supporting grid computing environment

SAN storage area network: a high-speed storage network with centralized management
Oracle RAC and DG

Purpose of RAC

  • Provides instance level redundancy
  • Provide more system resources
  • Add more parallel processing

Advantages and disadvantages of RAC


  • Provide system redundancy
  • More system resources
  • Business segmentation processing


  • Memory sharing and resource competition
  • The underlying technology is complex and requires high DBA technology

When does RAC need to be used?

  • Instance redundancy — the purpose of the first consideration
  • Improvement of processing capacity and performance



DataGuard, a database level high availability (HA) solution, is used as a data disaster recovery solution. For online transaction processing (OLTP, the amount of data is not too large), for online analytical processing (OLAP, the amount of data is too large), you can only select key data to create DG, conventional data, select other backup methods.

DG of disaster tolerance level:

Oracle RAC and DG

Local, same city, different places, multiple disaster recovery, creating a lot of standby

Protection mode of DataGuard

Maximum protection mode

The most secure mode, in which the data between the master database and the standby database is synchronized. That is, when the primary database is submitted, the standby database will be restored accordingly. The data integrity is guaranteed to the maximum extent. Data loss is not allowed.

If the network between the primary database and the standby database, or if there is a problem in the standby database, the operation of the primary database will be directly affected. The main database is down. Therefore, the maximum protection mode will not be selected.

Maximum performance mode

This mode ensures the maximum performance of the primary database, and the data between the primary database and the standby database is asynchronous. In other words, the primary and secondary logs will be transferred to the standby database after archiving, and the archive log files will be used for recovery operation on the standby database.

Highest availability mode

This mode is basically similar to “maximum protection”. Under normal circumstances, the primary and secondary databases are synchronized.

In case of network or standby database problems, the downtime of the primary database will not be affected. The primary database will automatically switch to the “maximum performance” mode. When the standby database is available, the archive will be transferred to the standby database for recovery.

This mode can be understood as the intermediate of “maximum protection” and “maximum performance”.

How to select the protection mode of DG

The biggest factor affecting the selection of DG protection mode is network quality. If the network quality is good, such as local LAN, the highest available mode can be selected. If the network quality is moderate, select the maximum performance mode. Generally, the maximum protection mode will not be selected, which damages the usability of the system.

Types of standby database in DG

Physical standby databases: Physical Standby Databases

Physical Standby is as like as two peas in Primary database.Maintain physical standby database through redo application (which belongs to block to block application)

Logical standby databases

Logical standby is also created through the primary database (or its backup, or its replication library, such as physical standby), so it is similar to the physical standby database at the beginning of creation. But becauseLogical standby applies redo data through SQL applicationTherefore, the physical file structure of logical standby and even the logical structure of data can be inconsistent with that of primary.


On DataGuard of oracle11gr2_ 03 the exploration of three protection modes can be seen in the following blog

Exploring DataGuard of oracle11gr2_ 03 three protection modes

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Oracle RAC and DG

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Oracle RAC and DG

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