In Oracle 12c Release 1 Undo tablespace was always Shared across PDBs. Rollback segment of each pdb was written in Undo tablespace which was created under the Container Root database.

Oracle 12.2 comes with a new Feature that allows Local Undo creation and Shared undo creation.

Local Undo tablespace to PDB helps us in the following way :

  1. When we want to do Hot Cloning of Pluggable Database.
  2. Performing near zero downtime PDB relocation.
  3. While Refreshing PDBs
  4. Using Proxy PDBs.

We can CDB for Local undo mode at the time of CDB database creation or by altering LOCAL_UNDO_ENABLED property.

LOCAL_UNDO_ENABLED property is disabled by default and only one Undo tablespace is created under Root.

Use the following steps to enable LOCAL_UNDO mode :

Step 1: Check property LOCAL_UNDOENABLED.

Step 2: To change local_undo mode we need to shutdown database gracefully

Shut down the database.

Step 3: Start database in upgrade mode

Step 4: Use alter database local undo on  to enable local undo mode

Step 5: Shut down the database

Step 6: Start the database in normal mode

Step 7: Check local_undo mode

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