Oracle 9i Database Failover

[Kaustubh Kane]

Hi,
We have a Primary and Physical Standby Oracle Databases. We need to understand the exact scenarios when Data Guard Failover should be used.
I did some search on web and following is the brief info I got:
Data Guard Failover should be used only when:
1) Switchover is not possible
2) Site disasters
3) Data Failures.

Could please give me more details on when the Data Guard Failover should be used?
Also let me the exact commands that should be used to perform a Data Guard Failover.

Thanks and regards,
Kaustubh Kane.

[Ben Dehner]

First, I want to be clear about a "switchover" and a "failover". Basically, a switchover is a reversible transition of standby to primary and primary to standby. A failver is an irreverisible transition of the standby to the primary.

With a switchover, a second switchover operation can be performed to put the primary database back on the original system. With a failover, there is no fallback. You need to re-copy the database back to the original system, although at that time a new dataguard configuration can be set up for a switch or fail back.

Oracle recommends that you should use the switchover when possible; however, your exact requirements may vary. The primary requirement is that the switchover must be initiated on the primary database, with the following sql (on 9i):

alter database commit to switchover to physical standby;

If the primary database is unavailable due to some outtage, then obviously this is not possible, and you must do a failover.

For a failover, there are a few basic steps; I'd suggest reviewing Chapter 7 (Role Management) in Oracle Data Guard "Concepts and Administration" reference at
http://download-east.oracle.com/docs/cd/B10501_01/server.920/a96653.pdf

1) first, make sure all archive/redo logs are transferred to the standby system. Logfiles must be manually registered if necessary.

2) issue the following two sql statements:
alter database recover managed standby finish;
alter database commit to switchover to primary;

-- at this point the database can no longer be used as a standby, there's no going back.

3) restart the database with
shutdown immediate;
startup;