Cloning a Pluggable Database (PDB) Across CDBs via Database Link

Applies to: Oracle Database 19c (Standard/Enterprise Edition), multitenant architecture Status: Draft / Verified in test

Overview

This runbook documents cloning a source PDB into a new target PDB using a remote clone over a database link. The source PDB remains online and read-write throughout — no downtime on the source is required. Destination datafiles are placed on a dedicated target filesystem/mount.

This method works because Oracle 12.2+ supports cloning a PDB that is open read-write; Oracle reconstructs a consistent copy using the source's redo stream, similar to RMAN DUPLICATE ... FROM ACTIVE DATABASE.

Placeholders used in this document:

Prerequisites

• Source and destination CDBs reachable over SQL*Net.

• Same Oracle version, same platform/endianness, matching character sets between CDBs.

• Sufficient free space on <DEST_MOUNT> for the cloned datafiles.

• LOCAL_UNDO_ENABLED = TRUE on the source CDB (mandatory since 12.2).

• Common user on the source CDB with CREATE PLUGGABLE DATABASE privilege, used solely to authenticate the DB link.

Procedure

1. Add a TNS alias for the source CDB (on the destination host)

Add to tnsnames.ora on the destination host:

<SOURCE_CDB> =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = <SOURCE_HOST>)(PORT = 1521))
    (CONNECT_DATA = (SERVER = DEDICATED)(SERVICE_NAME = <source_cdb_service_name>))
  )

Verify connectivity:

tnsping <SOURCE_CDB>

2. Create a common user on the source CDB

Run on the source CDB as SYS:

CREATE USER <LINK_USER> IDENTIFIED BY <LINK_PASSWORD> CONTAINER=ALL;
GRANT CREATE SESSION, CREATE PLUGGABLE DATABASE TO <LINK_USER> CONTAINER=ALL;

3. Confirm LOCAL_UNDO is enabled on the source

SELECT property_value FROM database_properties WHERE property_name = 'LOCAL_UNDO_ENABLED';

Expected: TRUE. The source PDB stays open read-write for the entire operation — no shutdown required.

4. Create the database link (on the destination CDB)

ALTER SESSION SET CONTAINER = CDB$ROOT;

CREATE DATABASE LINK <DB_LINK_NAME>
  CONNECT TO <LINK_USER> IDENTIFIED BY <LINK_PASSWORD>
  USING '<SOURCE_CDB>';

Test:

SELECT * FROM dual@<DB_LINK_NAME>;

5. Confirm the destination filesystem is ready

ls -ld <DEST_MOUNT>
df -h <DEST_MOUNT>

6. Check and set db_create_file_dest before cloning

⚠️ Critical step — see Lessons Learned below.

SHOW PARAMETER db_create_file_dest;

Set it to the intended destination:

ALTER SYSTEM SET db_create_file_dest = '<DEST_MOUNT>' SCOPE=BOTH;

Do not reset this parameter to NULL — an unset db_create_file_dest combined with PATH_PREFIX produces ORA-65016: FILE_NAME_CONVERT must be specified on a remote (DB link) clone.

7. Run the clone

ALTER SESSION SET CONTAINER = CDB$ROOT;

CREATE PLUGGABLE DATABASE <TARGET_PDB>
  FROM <SOURCE_PDB>@<DB_LINK_NAME>;

Files are created under <DEST_MOUNT>/<DEST_CDB_NAME>/<GUID>/datafile/... (standard OMF naming, rooted at db_create_file_dest).

If a specific subdirectory is required (e.g. <DEST_MOUNT>/<TARGET_PDB>/), do not rely on PATH_PREFIX for a remote/DB-link clone — it did not override db_create_file_dest in testing. Use FILE_NAME_CONVERT instead, after retrieving the source's actual file paths:

SELECT file_name FROM cdb_data_files@<DB_LINK_NAME>
WHERE con_id = (SELECT con_id FROM v$pdbs@<DB_LINK_NAME> WHERE name = '<SOURCE_PDB>');

CREATE PLUGGABLE DATABASE <TARGET_PDB>
  FROM <SOURCE_PDB>@<DB_LINK_NAME>
  FILE_NAME_CONVERT = ('<source_path_prefix>', '<DEST_MOUNT>/<DEST_CDB_NAME>/<TARGET_PDB>/');

8. Open the new PDB

ALTER PLUGGABLE DATABASE <TARGET_PDB> OPEN;

9. Save state (auto-open on CDB restart)

ALTER PLUGGABLE DATABASE <TARGET_PDB> SAVE STATE;

10. Verify

SELECT name, open_mode, restricted FROM v$pdbs WHERE name = '<TARGET_PDB>';

SELECT file_name FROM cdb_data_files
WHERE con_id = (SELECT con_id FROM v$pdbs WHERE name = '<TARGET_PDB>');

Confirm every datafile path starts with <DEST_MOUNT>/.... Spot-check row counts against the source PDB to confirm data consistency.

11. Cleanup

DROP DATABASE LINK <DB_LINK_NAME>;
DROP USER <LINK_USER> CASCADE;

Only run this if the link/user are one-time use; skip if they'll be reused for future clones.

Lessons Learned / Troubleshooting

Key takeaway: For remote PDB clones over a DB link in 19c, db_create_file_dest is the authoritative control for OMF file placement. Set it explicitly before cloning rather than depending on PATH_PREFIX.

Rollback

To remove the target PDB entirely:

ALTER PLUGGABLE DATABASE <TARGET_PDB> CLOSE IMMEDIATE;
DROP PLUGGABLE DATABASE <TARGET_PDB> INCLUDING DATAFILES;

The source PDB is never altered during this procedure, so no source-side rollback is needed.