一、DG 3种模式的LOG_ARCHIVE_DEST_n 设置

Maximum Availability	Maximum Performance	Maximum Protection
AFFIRM	NOAFFIRM	AFFIRM
SYNC	ASYNC	SYNC
DB_UNIQUE_NAME	DB_UNIQUE_NAME	DB_UNIQUE_NAME

Execute the following SQL statement on the primary database:
SQL> ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE {AVAILABILITY | PERFORMANCE | PROTECTION};

Note that the data protection mode can be set to MAXIMUM PROTECTION on an open database only if the current data protection mode is MAXIMUM AVAILABILITY and if there is at least one synchronized standby database.

SELECT PROTECTION_MODE FROM V$DATABASE;

参考文档：http://docs.oracle.com/cd/E11882_01/server.112/e41134/protection.htm#SBYDB4744

二、DATAGUARD 的实时应用REDO LOG

DATAGUARD 的实时应用REDO LOG，与 DATAGUARD的3种模式无关。具备两个条件即可：
（1）有standby redo log ，select * from v$standby_log
（2）处于ARCHIVELOG 模式。
（3）ALTER DATABASE 语句启用实时应用REDO LOG.

Use the ALTER DATABASE statement to enable the real-time apply feature, as follows:
For physical standby databases： ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE statement.
For logical standby databases： ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE statement.

官方文档：
http://docs.oracle.com/cd/E11882_01/server.112/e41134/log_apply.htm#SBYDB4762
Using Real-Time Apply to Apply Redo Data Immediately

If the real-time apply feature is enabled, apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. This results in faster switchover and failover times because the standby redo log files have been applied already to the standby database by the time the failover or switchover begins.

Use the ALTER DATABASE statement to enable the real-time apply feature, as follows:

For physical standby databases, issue the ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE statement.
For logical standby databases, issue the ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE statement.

Real-time apply requires a standby database that is configured with a standby redo log and that is in ARCHIVELOG mode.

Figure 7-1 shows a Data Guard configuration with a local destination and a standby destination. As the remote file server (RFS) process writes the redo data to standby redo log files on the standby database, apply services can recover redo from standby redo log files as they are being filled.

Figure 7-1 Applying Redo Data to a Standby Destination Using Real-Time Apply

Description of "Figure 7-1 Applying Redo Data to a Standby Destination Using Real-Time Apply"

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DATAGUARD 3种模式的以及REDO LOG实时应用

一、DG 3种模式的LOG_ARCHIVE_DEST_n 设置

二、DATAGUARD 的实时应用REDO LOG

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