Data Guard logical cascaded standby databases Oracle Database Tips by Donald BurlesonDecember 9, 2015

 Oracle Data Guard:  Using Logical Standby Databases for Cascaded Standby Databases

The setup for transmitting archived redo logs from a logical Oracle instance to the cascaded archive destination is similar to the one explained above for the physical standby database with the exception that a logical Oracle instance cannot have standby redo logs.  Therefore, the ARCH process from the primary database sends archived redo logs to the standby site. In this case, if the init.ora file of the logical Oracle instance contains any archive destination pointing to other standby databases created directly from the primary database, these should be set to DEFER.

The archived redo logs produced by the logical Oracle instance contain only the filtered data that has been generated and applied by SQL Apply operation. Because two layer of filtering are being introduced when a cascaded logical standby database is created from a logical standby database, the cascaded logical Oracle instance may contain a very small set of objects from the primary database. Similarly, a cascaded physical standby database created from a logical Oracle instance may not represent the actual primary database in its entirety.

Conclusion

This chapter dealt with the administration of standby databases. The topics covered in detail are as follows:

• General administration of physical and logical standby databases.
   

• Manually applying changes on standby databases that cannot be transmitted using log management services.
   

• Monitoring of log management services on standby databases.
   

• Determining and resolving archive gap sequence.
   

• Cascaded standby databases.

The next chapter will present log management services in detail.