Active Data Guard and Undo and ora-01555

Question

Hi
We have an 11.1.0.7 two-node RAC primary with a single instance Active Data Guard physical standby. When running a datapump export from the standby, we get an ORA-01555 although the undo_retention is set way beyond the run time for the export.
I'm looking to better understand undo within the context of Active Data Guard. Is there any dependency for undo between the primary(s) and standby? Are the undo settings (undo_retention, undo tablespace size..) on the primary and standby independent of each other?
Thanks.

Answer 1

The standby is a Physical Standby. An exact copy of the Primary. The undo at the standby is controlled by the redo coming from the Primary. When the undo gets overwritten at the Primary it gets overwritten at the standby regardless of what is running there. You can't have undo kept around longer at the standby, it is an EXACT copy of the Primary.
Increasing the undo tablespace and the undo_retention at the Primary will allow more undo to be kept at both the Primary and the Standby but the standby is still controlled by the Primary's management of the undo. Of course you should change the parameter at the standby too so that everything behaves the same when you make the standby a Primary database.
Hope this helps.
Larry