Ensure that you have completed these database preparation tasks before starting an Oracle Database upgrade.

• Patch Set Updates and Requirements for Upgrading Oracle Database
  Before starting upgrades, update your new release Oracle Database to the latest Oracle bundle patch, patch set update (BP or PSU), or Release Update (Update), or Release Update Revision (Revision).
• Copying Transparent Encryption Oracle Wallets
  If you use Oracle wallet with Transparent Data Encryption (TDE), then copy the sqlnet.ora and wallet file to the new Oracle home.
• Recommendations for Oracle Net Services When Upgrading Oracle Database
  Review these procedures and parameter changes for Oracle Net Services before you upgrade.
• Understanding Password Case Sensitivity and Upgrades
  By default, Oracle Database 12c Release 2 (12.2) and later releases are upgraded to an Exclusive Mode. Exclusive Modes do not support case-insensitive password-based authentication.
• Checking for Accounts Using Case-Insensitive Password Version
  Use these procedures to identify if the Oracle Database that you want to upgrade has accounts or configuration parameters that are using a case-insensitive password version.
• Running Upgrades with Read-Only Tablespaces
  Use the Parallel Upgrade Utility with the -T option to take schema-based tablespaces offline during upgrade.