Oracle Data Guard Switchover

Posted on 2011-09-12
Last Modified: 2012-06-27
I have a multiple point question looking for confirmation of the research I've done.  I am about to do a switchover from a primary db to a standby db because of updates that need to be applied to the server.  It seems that I have redo apply running on the standby.  I have also found the commands to switch the primary to standby and standby to primary.  My main concern is at this point is that once the reboot occurs and we bring up the current primary it will be the standby and this will have to be changed soon thereafter.  How do i know if the current primary will be in sync and have all current data applied before make the second switchover and if it is not how do you go about ensuring that this will happen in timely manner?  Also do I need to make sure the services currently running on the standby are running on the current primary, i.e. redo apply so that when it comes up in standby it will work correctly?

Please excuse my ignorance but I have only worked with standalone before and I'm having to learn this on the job and cannot afford to have down time due to the importance of the data being needed.
Question by:geleman
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LVL 48

Expert Comment

ID: 36522849
I think the only clean way to do this is to stop the primary and to switch the standby from "managed recovery mode" to normal database mode.

After that the best way will be to install standby on the place of the former primary and to direct the archived redo logs from the former standby to the former primary.

Looking in the net there are some articles that can give you details of the switchover.
LVL 35

Expert Comment

ID: 36522898
Have you checked the documentation on switchovers:

It is pretty detailed.

Keep in mind that a switchover and a failover are 2 different things.  We are really looking at a switchover here.  Done the way the documentation describes, there is no data loss during a switchover.  Oracle makes sure that everything is applied on both sides.  I would set it all up in a test environment to get yourself comfortable with the commands and switching back and forth.
LVL 35

Expert Comment

ID: 36522912
What schwertner is describing is a failover.
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Author Comment

ID: 36523157

I can see that if doing the switchover and the server staying up how there wouldn't be any data loss be once we do the switch over we have to immediately reboot the server.  So there will be some difference between the 2 when I bring the db back up after the reboot.  How do I ensure the data is the same once I bring it back up and do the switchover again to make the original primary the primary again.  This is only a temporary situation for updates only so it will need to be switched back as soon as I know the data is updated and the same at that point.
LVL 35

Expert Comment

ID: 36523241
Once you bring up the old primary (now designated a standby), you would need to start the managed recovery there and make sure that all the logs got across from the down time.  Once they were across and applied, you could do the switchover again to take things back to the way they were.

Author Comment

ID: 36524760

One last question.  If all sessions are killed and and not new logins are issued for both databases is it necessary for a switchover if there will be no new data coming?
LVL 35

Accepted Solution

johnsone earned 500 total points
ID: 36525083
That depends.  Your original question says you are doing a switchover because "updates that need to be applied to the server".  That would imply to me that the database and server need to be shut down during that time.

If you do not do a switchover, your database will not be accessible while it is down.  If you can take that kind of downtime, then leave everything down and don't do the switchover.

The switchover would only be necessary if you wanted everything to run normally during your downtime.  Of course, there is still down time to do the switchover and the to switchover again to bring it back, but that would be less than your total maintenance downtime.

Author Closing Comment

ID: 36525113
I appreciate all the help you answered everything I needed to know and was not sure about.  Thank you very much.

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