Local UNDO Mode Versus Shared UNDO Mode
Using the local UNDO mode is required when cloning a PDB in hot mode or performing a near-zero downtime PDB relocation or refreshing PDBs or using proxy PDBs.
You can set a CDB in local UNDO mode either at CDB creation or by altering the CDB property.
When the database property LOCAL_UNDO_ENABLED is FALSE, which is the default, there is only one UNDO tablespace that is created in the CDB root and that is shared by all containers.
When LOCAL_UNDO_ENABLED is TRUE, every container in the CDB uses local undo and each PDB must have its own local UNDO tablespace. To maintain ease of management and provisioning, UNDO tablespace creation happens automatically and does not require any action from the user. When a PDB is opened and an UNDO tablespace is not available, it is automatically created.
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Categories: Oracle 12cR2 New Features