Cascading standby destinations




A cascaded standby database is a standby database that receives primary database redo indirectly, from a cascading physical standby database, rather than directly from a primary database.

Cascading can reduce network bandwidth consumption by eliminating duplicate redo transmission over network links that are shared by more than one standby database.

I used this method after I successfully created a physical standby from a backup that was running against another physical standby; all RMAN backups are configured to run against the physical standby.  I needed to get some archivelogs to synch up primary with new standby; the archivelogs were no longer present on primary but were still located at the physical standby location.

Therefore, to configure it so that I could successfully synchronize the new standby with primary, I did the following:

Physical standby Database:

db_unique_name = prmy_stb


alter system set log_archive_config='DG_CONFIG=(prmy,prmy_stb,cscd_stb)' scope=both;
alter system set log_archive_dest_3='service=cscd_stb VALID_FOR=(STANDBY_LOGFILES,STANDBY_ROLE) DB_UNIQUE_NAME=cscd_stb' scope=both;

Cascaded standby Database:

db_unique_name = cscd_stb


alter system set log_archive_config='DG_CONFIG=(prmy,prmy_stb,cscd_stb)' scope=both;
alter system set fal_server=prmy_stb scope=both;

This worked flawlessly.

As a side note, cascading has the following restrictions:

1. Logical and snapshot standby databases cannot cascade primary database redo.

2. SYNC destinations cannot cascade primary database redo in a Maximum Protection Data Guard configuration.

3. Cascading is not supported in Data Guard broker configurations.




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