About Dataguard Online redo log and Standby redo log

Dataguard Online redo log and Standby redo log Dataguard classification: Physical Standby (Redo Apply) Logical Standby (SQL Apply) Dataguard protection mode: maximize performance (maximum performance mode) maximize availability (maximum available mode) maximize protection (maximum protection mode) Online redo log stores Unarchived changes of Online transactions. The master database must be configured. If it is Physical Standby, the Standby database cannot open read write, so the online redo log of the Standby database is almost useless. However, considering that the Standby database may switch to the primary database at any time, you must configure the online redo log; for Logical Standby, the Standby database can open read write, so you must configure online redo log. The Standby redo log remote file server (RFS) process of the standby database receives the redo data transmitted from the primary database and writes it to the Standby redo log, standby redo log is similar to the online redo log of the master database. It only stores the redo data transmitted from the master database in the slave database. If the master database may be switched to the slave database, the standby redo log must be configured for the master database. In the following three cases, the standby Database Configuration must be standby redo log: 1) In maximum protection and maximum availability mode; 2) in real-time application; 3) configure the Standby redo log when cascading uard is configured. The size of the Standby redo log is the same as that of the online redo log of the master database. The number of groups must be at least one more than the online redo log of the master database.