Real Time Exprience about DB Upgrade

Keep in mind there is two types of upgrade procedure

1. From lower oracle verion to higher oracle version

For eg:

Oracle 8i,9i,10g to oracle 11g

or

Oracle 8i,9i to oracle 10g

or

Oracle 8i to oracle 9i

or

so on.

2. patch set or cpu(critical patch update) upgrade.

it is always apply on same oracle version means if we are using oracle 10gr1 then we can apply only latest patchset for 10gr1

For eg:

If we are using oracle 8i (8.1.0) then we can apply only latest patch set for 8i is (8.1.7.4) patchset

If we are using oracle 9ir1(9.0.1) then we can apply only latest patch set for 9ir1 is(9.0.1.4) (not sure about latest patchset )

If we are using oracle 9ir2(9.2.0) then we can apply only latest patch set for 9ir2 is (9.2.0.7) same like10gr1 ---10.1.0.5.0, 10gr2 ---10.2.0.4.0 , 11gr1 ---N/A

according to me apply patchset is easy and safest task compare to upgrade from lower oracle version to higher oracle version.

Oracle enhanced with every new release so some feature in lower version are obsolete & desupported in higher version. Same like in higher version new features are introduced which are not exist in lower version. And upgrade/migrate is one of the important task for DBA. so we have to do it

I always recommended never ever upgrade directly PRODUCTION box without prior testing on TEST/DEV server.