Doubts about applying and removing patches
I was very happy to hear from SearchOracle.com about you and your experience with Oracle. I have some doubts about applying patches. I have Oracle 126.96.36.199.0 databases. I didn't apply any patch until now to the databases. Once I tried and got some errors, and I was not able to rollback to the previous stage of the database. So I am afraid that if I apply patches it will affect the current system. Is there any way to remove the applied patches? What are the main things that we have to be careful of while applying patches?
Patching or upgrading any database carries with it some inherent risk. To mitigate this risk, we patch in a development (or other non-production) environment before patching a production system. We stress sufficient testing before migrating the patch to production. And, finally, we take backups not only of the databases affected, but also the Oracle binaries about to be upgraded so that the environment can be recovered in the event that something goes wrong during the patching or upgrading process.
Having said that, it is important to stay as current as possible within the limits allowed by your applications. Some vendor products will only certify certain versions of Oracle so you must stay within those requirements. You will also notice that critical patch updates now being introduced on a quarterly basis from Oracle will only work on the latest versions. This is another good reason to try and keep your database at a current version.
With respect to your question of removing applied patches, you need to read the accompanying readme.txt files associated with each upgrade. They will usually indicate what you need to do to back out a patch or downgrade a database. In some cases (depending on the patch), the database can be downgraded or the patch can be rolled back. In other circumstances, the binaries and databases must be fully recovered to a point in time prior to the patch application.
This was first published in August 2005