PDB Cloning, Snapshot/Refresh Concepts, Unplug/Plug, Relocation, and Portability

Learning outcomes

ServiceHub needs a copy of production-like metadata for a test, then later must move a tenant to another CDB. “Clone the PDB” can mean a full file copy, a storage snapshot copy, a refreshable copy fed by redo, or the first phase of relocation. Unplug/plug is different again: it separates PDB metadata/files from one CDB and validates them against another. Choosing the mechanism requires storage, undo, downtime, compatibility, service, encryption, and topology evidence.

1. Full clone creates a new independent PDB copy

A normal CREATE PLUGGABLE DATABASE ... FROM source_pdb copies source PDB files to create an independent clone. If the source is open read/write, local undo mode is required for supported hot-clone workflows. If local undo is unavailable, use the documented source open-mode requirements rather than improvising.

ALTER SESSION SET CONTAINER=CDB$ROOT;SELECT property_name,property_valueFROM database_propertiesWHERE property_name='LOCAL_UNDO_ENABLED';SELECT value AS db_create_file_destFROM v$parameterWHERE name='db_create_file_dest';SELECT name,open_mode,total_sizeFROM v$pdbsWHERE name IN ('SH13LAB','FREEPDB1');

DBCA-created modern CDBs normally use local undo, but verify the actual property. Local undo means each PDB has its own undo tablespace and enables operations such as hot cloning/relocation more cleanly.

2. Optional local clone of the small disposable PDB

Run this only if Lesson 2 created a small SH13LAB, OMF is configured, LOCAL_UNDO_ENABLED=TRUE, and the Free 12-GB data limit/storage headroom are safe.

CREATE PLUGGABLE DATABASE sh13cloneFROM sh13lab;ALTER PLUGGABLE DATABASE sh13clone OPEN READ WRITE;ALTER PLUGGABLE DATABASE sh13clone SAVE STATE;SELECT pdb_name,status,source_pdb_nameFROM dba_pdbsWHERE pdb_name='SH13CLONE';SELECT name,open_modeFROM v$pdbsWHERE name='SH13CLONE';

The clone receives a new identity/GUID and default service. A successful clone does not prove that external connection pools or service naming are conflict-free across hosts/CDBs.

3. Snapshot copy is storage-dependent copy-on-write—not a generic fast clone

SNAPSHOT COPY uses storage snapshots so Oracle does not copy every source block initially. Current SQL syntax requires supported snapshot-capable storage configurations such as Oracle ACFS or Direct NFS arrangements, with additional rules depending on CLONEDB. Snapshot-copy clones depend on the source/snapshot relationship and have restrictions such as not being unplug-able.

CREATE PLUGGABLE DATABASE test_snapFROM source_pdbSNAPSHOT COPY;

The current licensing matrix separately lists PDB Snapshot Carousel as unavailable in Free. Do not equate every syntax containing the word snapshot with an entitlement to automated snapshot-carousel functionality.

4. Refreshable clones replay source redo and are normally read-only

A refreshable PDB is created from a remote source over a database link with REFRESH MODE MANUAL or a timed interval. Refresh applies source changes accumulated since the last refresh; the refreshable clone is opened read-only and must be closed for refresh. This is a topology workflow, not a second same-process Free database shortcut.

CREATE PLUGGABLE DATABASE servicehub_refreshFROM servicehub_prod@prod_root_linkREFRESH MODE EVERY 60 MINUTES;ALTER PLUGGABLE DATABASE servicehub_refresh CLOSE;ALTER PLUGGABLE DATABASE servicehub_refresh REFRESH;ALTER PLUGGABLE DATABASE servicehub_refresh OPEN READ ONLY;

The current licensing matrix says Refreshable PDB switchover is not available in Free. Also, Free permits only one installation per logical environment, so a two-CDB test requires separate logical environments if you use Free.

5. Unplug/plug separates metadata/files from CDB membership

Unplug writes PDB metadata to XML (or archive workflows) after the required close/state preparation. Plugging into a target CDB must pass compatibility checks covering versions, options/components, character sets, patch state, encryption/keystore details, and other constraints.

BEGIN  DBMS_PDB.DESCRIBE(    pdb_descr_file => '/u01/app/oracle/oradata/sh13lab.xml',    pdb_name       => 'SH13LAB'  );END;/

The path must be writable/readable by the Oracle database OS account and appropriate for your platform/container mount. Do not copy this Linux-style path blindly to Windows or an Oracle container with different mounts.

SET SERVEROUTPUT ONDECLARE  l_ok BOOLEAN;BEGIN  l_ok := DBMS_PDB.CHECK_PLUG_COMPATIBILITY(            pdb_descr_file => '/u01/app/oracle/oradata/sh13lab.xml',            pdb_name       => 'SH13LAB'          );  DBMS_OUTPUT.PUT_LINE(    'compatible=' || CASE WHEN l_ok THEN 'YES' ELSE 'NO' END  );END;/SELECT  name,cause,type,status,message,actionFROM pdb_plug_in_violationsWHERE name='SH13LAB'ORDER BY time,line;

A TRUE result is an important prerequisite, not proof that copy/move/NOCOPY file placement, services, TDE keys, backup catalog, network routing, or application cutover are correct.

6. Relocation combines remote clone, synchronization, and source removal

RELOCATE moves a PDB from a source CDB to a target CDB using a database link. The source can remain read/write during much of the operation; local undo and target/source prerequisites matter. The target CDB needs CREATE PLUGGABLE DATABASE, the link identity/privileges must be correct, and service/start-state planning is part of cutover.

7. Deliberately wrong: plug first, investigate violations later

Ignoring compatibility and patch warnings can leave a PDB unable to open normally or requiring upgrade/datapatch remediation during the outage. The repair is to generate/validate the descriptor in advance, review PDB_PLUG_IN_VIOLATIONS, verify target release/patch/options/TDE/storage/service assumptions, and run a rehearsal using a disposable copy.

8. Optional cleanup

ALTER SESSION SET CONTAINER=CDB$ROOT;ALTER PLUGGABLE DATABASE sh13clone CLOSE IMMEDIATE;DROP PLUGGABLE DATABASE sh13clone INCLUDING DATAFILES;

9. Production judgment

Use a full clone for independent copies, snapshot copy only when storage and lifecycle dependencies are acceptable, refreshable clones for lagged read-only copies with remote topology, unplug/plug for portability, and relocate for planned CDB-to-CDB movement. Record source/target CDB version, RU, COMPATIBLE, local-undo mode, character set, options/components, TDE/keystore mode, storage type, service names, file paths, and rollback.

No clone/relocation command is required for the mandatory path beyond metadata/compatibility design. Lesson 4 turns to runtime isolation: a PDB is an administrative/security boundary, but CPU, memory, redo, instance processes, and some identities/resources remain shared at the CDB/host layer.

Authoritative references

• CREATE PLUGGABLE DATABASE — clone, snapshot copy, refresh and relocate syntax/prerequisites
• Cloning a PDB — full and refreshable clone workflows
• Relocating a PDB — relocation topology and privileges
• Plugging In an Unplugged PDB — compatibility checking and plug lifecycle
• PDB_PLUG_IN_VIOLATIONS — compatibility warning/error evidence