Multitenant Pills: Partial PDB cloning (and cleanup)

When consolidating to multitenant, there are several consolidation patterns.

  • Big, complex databases usually have special requirements for which it might be a good choice to go to single-tenant (a single PDB in one CDB)
  • Small, relatively easy databases are the best candidate for consolidation to multitenant
  • Schema consolidated databases require special attention, but in general there are several advantages to convert individual schemas (or group of schemas) to individual PDBs

For the latter, there are some techniques to convert a schema in a PDB.

  • export/import (obviously), with eventually Golden Gate to do it online
  • Transportable tablespaces (if the schemas follow strict 1-to-1 tablespace separation
  • partial PDB cloning

We will focus on the last one for this blog post.


Here we have a PDB with some schemas, each of them has a dedicated tablespace, but accidentally, two of them have also some objects on a common tablespace.

This happens frequently when all the users have quota on the default database tablespace and they do not have necessarily a personal default tablespace.

This is the typical situation where transportable tablespaces become hard to achieve without some upfront segment movement, as tablespaces are not self-contained.

Thankfully, Oracle Multitenant allows us to clone a PDB from a remote one and specify only a subset of tablespaces.

Here is a full example script with some checks and fancy parameters:

This is an example output:

If the clone process succeeds, at the end we should have the new ABC pluggable database with ABC and DATA tablespaces only.


Any Cleanup needed?

What happened to the users? Actually, they are all still there:

And the segments in the two skipped tablespaces are not there:

So the table definitions are also gone?

Not at all! The tables are still there and reference to tablespaces that do not exist anymore. Possible?

Actually, the tablespaces definition are still there if we look at v$tablespace:

If we give a look at the DBA_TABLESPACES view definition, there are a few interesting filters:

What is their meaning?

So the first WHERE clause skips all the INVALID TABLESPACES (when you drop a tablespace it is still stored in ts$ with this state), the second skips the definition of TEMPORARY TABLESPACE GROUPS, the third one is actually our candidate.

Indeed, this is what we get from ts$ for these tablespaces:

So the two tablespaces are filtered out because of this new multitenant flag.

If we try to drop the tablespaces, it succeeds:

But the user GHI, who has no objects anymore, is still there.

So we need to drop it explicitly.

Automate the cleanup

This is an example PL/SQL that is aimed to automate the cleanup.


  • Users that had segments in one of the excluded tablespaces but do not have any segments left are just LOCKED (for security reasons, you can guess why).
  • Tablespaces that meet the “excluded PDB” criteria, are just dropped

This is the output for the clone procedure we have just seen:

The PL/SQL block can be quite slow depending on the segments and tablespaces, so it might be a good idea to have a custom script instead of this automated one.

What about user DEF?

The automated procedure has not locked the account DEF. Why?

Actually, the user DEF still has some segments in the DATA tablespace. Hence, the procedure cannot be sure what was the original intention: copy the user ABC ? The clone procedure allows only to specify the tablespaces, so this is the only possible result.

Promo: If you need to migrate to Multitenant and you need consulting/training, just contact me, I can help you 🙂


Multitenant Pills: Pushing your PDB to the Cloud in one step?

The Oracle Multitenant architecture introduces some nice opportunities, including local and remote cloning (see this example on ORACLE_BASE blog).

However, the only available cloning procedure use the PULL method to get the data from the remote source PDB.

This can be a limitation, especially in environments where the cloning environment does not have direct access to the production, or where the clones must be done in the Cloud with no direct access to the production VLAN on-premises.

So, one common approach is to clone/detach locally, put the PDB files in the Object Store and then attach them in the cloud.

Another approach is to use SSH tunnels. If you follow my blog you can see it is something that I use every now and then to do stuff from on-premises to the cloud.

How to set it up?

Actually, it is super-easy: just prepare a script in the cloud that will do the create pluggable database, then trigger it from on-premises.

This is an example:

It takes as parameters: the name of the source PDB, the name of the target PDB and the SQL*Net descriptor to create the temporary database link from the cloud CDB to the on-premises CDB.

The user C##ONPREM must obviously exist on-premises with the following privileges:

The cloud database should use OMF so you don’t have to take care about file name conversions.

At this point, if you have set up correctly the SSH keys to connect to the cloud server, it is just a matter of running the script remotely using the proper SSH tunnel. Once the remote port binding established, the cloud server can contact the on-premises listener port using localhost:remote_bind:

Of course the timing depends a lot on the size of the database and your connection to the Cloud.

I have tested this procedure with Oracle Database 19.7 on OCI compute instances and on DBaaS VM instance, it works without any additional work. Of course, it does not work for Autonomous Database 🙂


Cloning a PDB with ASM and Data Guard (no ADG) without network transfer

Ok, if you’re reading this post, you may want to read also the previous one that explains something more about the problem.

Briefly said, if you have a CDB running on ASM in a MAA architecture and you do not have Active Data Guard, when you clone a PDB you have to “copy” the datafiles somehow on the standby. The only solution offered by Oracle (in a MOS Note, not in the documentation) is to restore the PDB from the primary to the standby site, thus transferring it over the network. But if you have a huge PDB this is a bad solution because it impacts your network connectivity. (Note: ending up with a huge PDB IMHO can only be caused by bad consolidation. I do not recommend to consolidate huge databases on Multitenant).

So I’ve worked out another solution, that still has many defects and is almost not viable, but it’s technically interesting because it permits to discover a little more about Multitenant and Data Guard.

The three options

At the primary site, the process is always the same: Oracle copies the datafiles of the source, and it modifies the headers so that they can be used by the new PDB (so it changes CON_ID, DBID, FILE#, and so on).

On the standby site, by opposite, it changes depending on the option you choose:

Option 1: Active Data Guard

If you have ADG, the ADG itself will take care of copying the datafile on the standby site, from the source standby pdb to the destination standby pdb. Once the copy is done, the MRP0 will continue the recovery. The modification of the header block of the destination PDB is done by the MRP0 immediately after the copy (at least this is what I understand).


Option 2: No Active Data Guard, but STANDBYS=none

In this case, the copy on the standby site doesn’t happen, and the recovery process just add the entry of the new datafiles in the controlfile, with status OFFLINE and name UNKNOWNxxx.  However, the source file cannot be copied anymore, because the MRP0 process will expect to have a copy of the destination datafile, not the source datafile. Also, any tentative of restore of the datafile 28 (in this example) will give an error because it does not belong to the destination PDB. So the only chance is to restore the destination PDB from the primary.

Option 3: No Active Data Guard, no STANDBYS=none

This is the case that I want to explain actually. Without the flag STANDBYS=none, the MRP0 process will expect to change the header of the new datafile, but because the file does not exist yet, the recovery process dies.
We can then copy it manually from the source standby pdb, and restart the recovery process, that will change the header. This process needs to be repeated for each datafile. (that’s why it’s not a viable solution, right now).


Let’s try it together:

The Environment



The current user PDB (any resemblance to real people is purely coincidental 😉 #haveUSeenMaaz):

Cloning the PDB on the primary

First, make sure that the source PDB is open read-only

Then, clone the PDB on the primary without the clause STANDBYS=NONE:

Review the clone on the Standby

At this point, on the standby the alert log show that the SYSTEM datafile is missing, and the recovery process stops.

One remarkable thing, is that in the standby controlfile, ONLY THE SYSTEM DATAFILE exists:

We need to fix the datafiles one by one, but most of the steps can be done once for all the datafiles.

Copy the source PDB from the standby

What do we need to do? Well, the recovery process is stopped, so we can safely copy the datafiles of  the source PDB from the standby site because they have not moved yet. (meanwhile, we can put the primary source PDB back in read-write mode).

Copy the datafiles:

Do the magic

Now there’s the interesting part: we need to assign the datafile copies of the maaz PDB to LUDO.

Sadly, the OMF will create the copies on the bad location (it’s a copy, to they are created on the same location as the source PDB).

We cannot try to uncatalog and recatalog the copies, because they will ALWAYS be affected to the source PDB. Neither we can use RMAN because it will never associate the datafile copies to the new PDB. We need to rename the files manually.

It’s better to uncatalog the datafile copies before, so we keep the catalog clean:

Then, because we cannot rename files on a standby database with standby file management set to AUTO, we need to put it temporarily to MANUAL.

standby_file_management is not PDB modifiable, so we need to do it for the whole CDB.

then we need to set back the standby_file_management=auto or the recover will not start:

We can now restart the recovery.

The recovery process will:
– change the new datafile by modifying the header for the new PDB
– create the entry for the second datafile in the controlfile
– crash again because the datafile is missing

We already have the SYSAUX datafile, right? So we can alter the name again:

This time all the datafiles have been copied (no user datafile for this example) and the recovery process will continue!! 🙂 so we can hit ^C and start it in background.

The Data Guard configuration reflects the success of this operation.

Do we miss anything?

Of course, we do!! The datafile names of the new PDB reside in the wrong ASM path. We need to fix them!


I know there’s no practical use of this procedure, but it helps a lot in understanding how Multitenant has been implemented.

I expect some improvements in 12.2!!