1 illustrates
Data Guard maximum availability supports the use of the NOAFFIRM redo transport attribute. A standby database returns receipt acknowledgment to its primary database as soon as redo is received in memory. The standby database does not wait for the Remote File Server (RFS) to write to a standby redo log file.
when the maximum support available NOAFFIRM redo DG transport properties, as long as the received standby database redo stored in memory, the library will return to the main reception confirmation. RFS process does not need to be written to the redo log file.
This feature provides increased primary database performance in Data Guard configurations using maximum availability and SYNC redo transport. Fast Sync isolates the primary database in a maximum availability configuration from any performance impact due to slow I/O at a standby database.
Fast Sync make maximum available in the primary database will not be affected by the library on the I / O's. Without sacrificing too much performance to improve data security. This feature is introduced, it is normally sufficient to meet needs. Unless special circumstances will result in data loss disaster, such as: the main library failure, data transmission equipment library in memory, not enough time to write the log file, prepared by the library also restart or power failure, it will resulting in loss of data (data inconsistency).
About the maximum available, refer to the official document: http://docs.oracle.com/database/121/SBYDB/protection.htm#SBYDB4743
When a transport is performed using SYNC/NOAFFIRM, the primary performs write operations and waits only for acknowledgement that the data has been received on the standby, not that it has been written to disk. The SYNC/NOAFFIRM transport can provide a performance benefit at the expense of potential exposure to data loss in a special case of multiple simultaneous failures.
With the possibility of losing data in exchange for performance improvements. According to the situation and traffic data from the selected row.
Redo transfer properties in the following table, the various modes of protection
| Maximum Availability | Maximum Performance | Maximum Protection |
|---|---|---|
| AFFIRM or NOAFFIRM | NOAFFIRM | AFFIRM |
| SYNC | ASYNC | SYNC |
| DB_UNIQUE_NAME | DB_UNIQUE_NAME | DB_UNIQUE_NAME |
grammar:
ALTER SYSTEM SET log_archive_dest_2='SERVICE=DG SYNC NOAFFIRM VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DG_P';
ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE AVAILABILITY;