Data Guard Protection Modes

Maximum Availability

This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Under normal operations, transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log AND based on user configuration, one of the following is true:

  • redo has been received at the standby, I/O to the standby redo log has been initiated, and acknowledgement sent back to primary
  • redo has been received and written to standby redo log at the standby and acknowledgement sent back to primary

If the primary does not receive acknowledgement from at least one synchronized standby, then it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.

If the primary database fails, then this mode ensures no data loss occurs provided there is at least one synchronized standby in the Oracle Data Guard configuration. See Performance Versus Protection in Maximum Availability Mode for information about the redo transport settings necessary to support Maximum Availability and associated trade-offs.

Transactions on the primary are considered protected as soon as Oracle Data Guard has written the redo data to persistent storage in a standby redo log file. Once that is done, acknowledgment is quickly made back to the primary database so that it can proceed to the next transaction. This minimizes the impact of synchronous transport on primary database throughput and response time. To fully benefit from complete Oracle Data Guard validation at the standby database, be sure to operate in real-time apply mode so that redo changes are applied to the standby database as fast as they are received. Oracle Data Guard signals any corruptions that are detected so that immediate corrective action can be taken.

Maximum Protection

Maximum protection is similar to maximum availability but provides an additional level of data protection in the event of multiple failure events. Unlike maximum availability, which allows the primary to continue processing if it is unable to receive acknowledgement from a standby database, maximum protection shuts the primary database down rather than allowing it to continue processing transactions that are unprotected.

Because this data protection mode prioritizes data protection over primary database availability, Oracle recommends that a minimum of two standby databases be used to protect a primary database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.

Note:

Asynchronously committed transactions are not protected by Oracle Data Guard against loss until the redo generated by those transactions has been written to the standby redo log of at least one synchronized standby database.

For more information about the asynchronous commit feature, see:

 

Maximum Performance

This protection mode provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).

This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.

This is the default protection mode.