【Oracle11g官方文档中关于Dataguard 最高可用模式的介绍】

This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to the standby redo log on at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, 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.

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.

【实验环境】

【主库、物理备库结构信息】

【实验过程】

主库 Primary database：绿色
物理备库 Physical standby database:黄色

1、查询主、备库角色和状态

2、模拟故障，主库停止向远程传归档

alter system set log_archive_dest_state_2=defer;

show parameter log_archive_dest_stat_2

 
3、查看状态和当前保护级别

主库查看发现，protection_mode仍然是最高可用模式，但当前protection_level显示resynchronization
即保护模式的目标没变，当前状态变了，需要同步。此时相当于 【最大性能模式】
select database_role,protection_mode,protection_level from v$database;

4、主库创建测试表，插入数据并提交

5、主、备库查看日志，备库一直在等待

6、主库开启远程归档

主库开启远程归档，查看保护模式，protection_level已经变成 maximum availability 最高可用模式

alter system set log_archive_dest_stat_2=enable; 
select database_role,protection_mode,protection_level from v$database;

7、查看跟踪日志、测试表

【实验总结】