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Don Burleson Blog 







Low downtime Oracle upgrade secrets

Oracle Database Tips by Donald BurlesonJune 2, 2015

Question: How do I do an Oracle upgrade with a low downtime?  I have a high availability non RAC database and I need to upgrade with very low downtime.

Answer:  Oracle has several low-downtime approaches to upgrades, the zero-downtime approach enables in RAC.  You can now upgrade or ASM RAC instances without shutting down the nodes using the new "alter system start rolling migration" syntax:

alter system start rolling migration to;

You can also use this minimum downtime trick as shown below.

Minimum-downtime rolling upgrade

Also see Minimizing downtime for Oracle release upgrades and rolling upgrades.

If you are staying on the same server, you can upgrade from 9i with about 5 minutes of downtime.  To do this, you will be using transportable tablespaces. The only requirement is that all your tablespaces are locally managed. The idea is simple.

1) Install Oracle to a separate Oracle Home on the same server

2) Create a database with only the base tablespaces: SYSTEM, SYSAUX, UNDO, and TEMP

3) On the 9i database, put all your tablespaces into read only mode (write downtime begins)

4) Perform a transportable tablespace export of all non-system tablespaces (as a sysdba user)

5) Shut down the 9i database (true downtime begins)

6) Start up the new database

7) Perform a transportable tablespace import into the new database (end true downtime)

8) Make all your tablespaces read/write (end write downtime)

This works from 9i to 10g because the newer datafiles are version aware. When you do the transportable tablespace export from 9i, all you are doing is dumping the datafile metadata to a dump file. When you import it to the new database, all you are doing is plugging in where to find the datafiles. The new version looks at the datafile headers, realizes that they're 9i, and changes the header to match the version. Since the new database already has SYSTEM, SYSAUX, UNDO, and TEMP, there's no downtime doing pesky data dictionary upgrades.

If you pre-script it all out, you can do all this with only about 5 minutes of downtime!

By the way, Dataguard's physical backups are a GREAT DR situation for a failed upgrade. You will have an exact physical copy of your database ready to switchover to if anything goes wrong with the upgrade. Basically you switch your final archive log and shut down your primary, then begin the standard upgrade. If something goes wrong, you can perform a failover on your standby server and you're back up with no possibility of inconsistencies since it's a physical backup. In my opinion, the only method better than DataGuard for a backup for upgrade scenario would be to use SAN tools like NetApp's snapMirror or Sun's Availability Suite in order to back it up; these tools can snapshot a DB in a matter of seconds and are good for this sort of situation: if the upgrade goes wrong, simply restore the snapshot.

If you do it right, you can set up dataguard with only 5 minutes of downtime, then perform your database upgrade with only 5 minutes of downtime. I have done this method for clients in the past and they have been very happy with the results.



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