Upgrade Companion - Read it first!
By Mike Dietrich-Oracle on Aug 10, 2009
Customers and Oracle partners were asking for a long time about a comprehensive note about upgrades. Often questions were raised such as "Why has this default setting changed and where has it been documented?", "How do I preserve performance information before the upgrade to ease diagnosis just in case something happens?" or "What's new with the optimizer?".
To answer these and many more questions in late 2007 the first Upgrade Companion for Oracle Database 10gR2 has been published on Metalink. Later the Companion for 11g got published as well - and as soon as Oracle Database 11gR2 gets released the Upgrade Companion will be available, too.
You'll find real Upgrade Best Practices from a technical perspective assisting you in planning your upgrade tasks carefully:
And - very important in the Behaviour Changes section- initialization parameter changes and very detailled description about optimizer behaviour:
It's always a good idea to read the Upgrade Companions before you start your upgrades.