Here’s a short and sweet post.
“In Deploy mode, AutoUpgrade also confirms that the upgrade has succeeded, and moves database files such as sqlnet.ora, tnsnames.ora, and listener.ora from the source home to the target home.
After these actions are complete, the upgraded Oracle Database release is started in the new Oracle home.”
Reference: About Oracle Database AutoUpgrade
To avoid issues caused by application failures, make a copy of sqlnet.ora, tnsnames.ora, and listener.ora from the source home.
Then, restore to source home as required.
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