[Oracle] Data Guard series (1)-three Protection Modes

[Oracle] Data Guard series (1)-three Protection modes Data Guard provides the following three Data Protection modes: 1) Maximum Protection) the "maximum protection" here refers to protecting data from loss to the maximum extent, that is, at least one standby and primary are synchronized in real time, but this is costly, as long as a transaction is committed, it should not only write the online redo log of the primary segment, but also write at least one standby redo log. In this case, there will be a serious problem, that is, when standby encounters a fault or network failure, causing log synchronization to fail, the primary database will be shut down, which is unacceptable in the production system, therefore, this mode is rarely used. 2) the highest Performance mode (Maximum Performance) is the opposite of the highest protection. When a transaction is committed, as long as the transaction is written to the primary online redo log, the primary is almost unaffected. Then synchronize the redo to standby, so that the primary and standby cannot be synchronized in real time. This mode is common in practical applications. After all, primary is not affected and is the most important. If standby lags behind primary too much, DBAs can intervene manually and apply redo on the standby side. 3) The highest Availability mode (Maximum Availability) is between the first and second Availability modes. Normally, it is the same as the highest protection mode, but once standby fails, switch to the highest-performance mode immediately, and primary will not shut down. If this mode is used, you need to pay attention to the performance impact of real-time applications on primary. How can I configure and modify the protection mode of DG? First, check whether db_unique_name of the master and slave databases is unique? 2. Does the dg_config attribute of log_archive_config contain all primary and backup databases db_unique_name? After confirming the preceding two points, you can use LOG_ARCHIVE_DEST_n to configure the parameter. The following table shows the relationship between this parameter and the protection mode, the maximum protection is the same as the highest availability configuration (this is normal because the highest availability is the maximum protection under normal circumstances): The LGWR process must be used to transmit Redo, and the network transmission mode must be sync, the disk write option is affrem. standby redo log must be configured. The maximum performance mode is flexible, that is, LGWR can be used, or redo can be transmitted using the ARCH process, the network can be sync or async, and the disk I/O write can be affrem or noaffrem, standby redo log is optional (recommended ). After confirming that all the above parameters are correctly configured, you can use the following statement to modify the protection mode:

[sql] ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE {AVAILABILITY | PERFORMANCE | PROTECTION};  

 

After the modification is successful, you can verify it using the following statement:

[sql] SELECT PROTECTION_MODE FROM V$DATABASE;