[Oracle] Introduction to three Data Guard 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, that is, when 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) Maximum Performance)
The highest performance is the opposite of the highest protection. When a transaction is committed, you only need to write the online redo log to the primary, and 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) Maximum Availability)
The highest availability mode is between the first and second modes. Normally, it is the same as the highest protection mode. However, if standby fails, it is immediately switched to the highest-performance mode and primary does not shut down. If this mode is used, you need to pay attention to the performance impact of real-time applications on primary.

In either mode, LOG_ARCHIVE_DEST_n is used for configuration. The relationship between them is shown in the table above. It can be seen that the maximum protection is the same as the highest availability configuration (because the highest availability is the maximum protection under normal conditions): 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.