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Oracle Dataguard provides three data protection modes. Here, we summarize the characteristics of the three data protection modes.

1. Maximum protection mode

1) this model provides the highest level of data protection

2) at least one physical standby database is required to receive the redo log before the transaction of the main database can be committed

3) when the master database cannot find a suitable backup library for writing, the master library will shut down automatically to prevent unprotected data from appearing.

4) advantage: this mode can ensure that there is no data loss in the standby database.

5) disadvantages: the automatic shutdown of the master library will affect the availability of the master library, and it can only be submitted after the backup library is restored, which requires very high objective conditions such as the network, which will have a great impact on the performance of the master library.

two。 Maximum availability mode

1) this mode provides data protection capability second only to "maximum protection mode".

2) at least one physical standby database is required to receive the redo log before the transaction of the main database can be committed

3) when the main library cannot find a suitable standby library to write, the main library will not be closed, but will be temporarily reduced to "maximum performance mode" mode until the problem is dealt with.

4) advantages: this mode can ensure that there is no data loss in the standby database without problems, and it is a compromise method.

5) disadvantage: in the process of normal operation, the disadvantage is that the performance of the main library is affected by many factors.

3. Maximum performance mode

1) this mode is the default mode and ensures the highest availability of the primary database.

2) ensure that the operation of the main database will not be affected by the standby database, the transaction of the main database will be committed normally, and the operation of the main database will not be affected by any problems in the standby database.

4) advantages: avoid the impact of standby database on the performance and availability of the primary database

5) disadvantages: if the recovery data related to the transactions committed by the main database are not sent to the standby database, the transaction data will be lost and no data loss can be guaranteed.

Description of the above three patterns in the official 4.oracle documentation

Http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/log_transport.htm#sthref553

The content is referenced here for reference.

5.6.1.1 Maximum Protection Mode

This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover each transaction must be written to both the local online redo log and to the standby redo log on at least one standby database before the transaction commits. To ensure data loss cannot occur, the primary database shuts down if a fault prevents it from writing its redo stream to at least one remote standby redo log. For multiple-instance RAC databases, Data Guard shuts down the primary database if it is unable to write the redo records to at least one properly configured database instance. The maximum protection mode requires that at least one standby instance has a standby redo log and the LGWR, SYNC, and AFFIRM attributes be used on the LOG_ARCHIVE_DEST_n parameter for this destination.

5.6.1.2 Maximum Availability Mode

This protection mode provides the highest level of data protection that is possible without compromising the availability of the primary database. Like maximum protection mode, a transaction will not commit until the redo needed to recover that transaction is written to the local online redo log and to at least one remote standby redo log. Unlike maximum protection mode, the primary database does not shut down if a fault prevents it from writing its redo stream to a remote standby redo log. Instead, the primary database operates in maximum performance mode until the fault is corrected and all gaps in redo log files are resolved. When all gaps are resolved, the primary database automatically resumes operating in maximum availability mode.

This mode ensures that no data loss will occur if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database.

Like maximum protection mode, the maximum availability mode requires that you:

* Configure standby redo log files on at least one standby database.

* Set the SYNC, LGWR, and AFFIRM attributes of the LOG_ARCHIVE_DEST_n parameter for at least 1 standby database.

5.6.1.3 Maximum Performance Mode

This protection mode (the default) provides the highest level of data protection that is possible without affecting the performance of the primary database. This is accomplished by allowing a transaction to commit as soon as the redo data needed to recover that transaction is written to the local online redo log. The primary database's redo data stream is also written to at least one standby database, but that redo stream is written asynchronously with respect to the commitment of the transactions that create the redo data.

When network links with sufficient bandwidth are used, this mode provides a level of data protection that approaches that of maximum availability mode with minimal impact on primary database performance.

The maximum performance mode enables you to either set the LGWR and ASYNC attributes, or set the ARCH attribute on the LOG_ARCHIVE_DEST_n parameter for the standby database destination. If the primary database fails, you can reduce the amount of data that is not received on the standby destination by setting the LGWR and ASYNC attributes.

5. Summary

When deploying Oracle Dataguard, we need to fully consider the impact on data and performance under the three protection modes in order to take advantage of advantages and avoid disadvantages. According to the specific analysis of the specific environment, each data protection mode has its own application. The default maximum performance mode is common, and systems running in this mode need to always pay attention to whether the backup database is missing. Usually, you can consider the method of "one primary belt with multiple backups" (a set of primary database corresponds to multiple standby databases) to ensure the integrity of the logs.

Good luck.

Secooler

10.10.12

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