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:
| Placeholder |
Description |
<SOURCE_CDB> |
TNS alias / service name of the source CDB |
<SOURCE_HOST> |
Hostname of the source database server |
<SOURCE_PDB> |
Name of the PDB being cloned |
<TARGET_PDB> |
Name of the new PDB being created |
<DEST_CDB_NAME> |
Name of the destination CDB |
<DEST_MOUNT> |
Target filesystem/mount point for datafiles (e.g. a dedicated data volume) |
<LINK_USER> |
Common user created on the source CDB for DB link authentication |
<LINK_PASSWORD> |
Password for <LINK_USER> |
<DB_LINK_NAME> |
Name of the database link created on the destination CDB |
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
| Issue |
Cause |
Resolution |
Datafiles created on the wrong mount despite PATH_PREFIX being specified |
db_create_file_dest was already set to a different path on the destination instance and took precedence over PATH_PREFIX |
Check SHOW PARAMETER db_create_file_dest before running CREATE PLUGGABLE DATABASE, and set it explicitly to the desired target path |
ORA-65016: FILE_NAME_CONVERT must be specified when using PATH_PREFIX |
db_create_file_dest was reset to NULL; for a remote (DB link) clone, PATH_PREFIX alone did not enable OMF-style file creation |
Keep db_create_file_dest set to a real path; don't rely on PATH_PREFIX overriding it for DB-link clones — use FILE_NAME_CONVERT if a custom path is required |
| Wrong-location clone already created |
N/A |
If no data had been written yet, cleanest fix is ALTER PLUGGABLE DATABASE <TARGET_PDB> CLOSE IMMEDIATE; then DROP PLUGGABLE DATABASE <TARGET_PDB> INCLUDING DATAFILES; and re-run the clone with corrected parameters |
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.
