Playing with Oracle 12c Multitenant Users and Roles

I’ve realized these days that the great list of articles by Oracle Alchemist does not contain any articles describing a little more in depth common roles and Users.

I’ve found these ones by Pete Finnigan and Bobby Curtis:

But I would like to investigate a little more.

My test environment

Just to give you an idea, I have two PDBs (HR and HR2), each containing an HR schema.

Creating the common user

As already pointed by the existing articles, I can’t create a common user into the root container without the c## prefix, unless I’m altering the hidden parameter _common_user_prefix.

so I specify the correct prefix, and it works:

The user is common, so it appears in all the containers, I can check it by querying CDB_USERS from the root container.

Creating the local user

Then I create also a local user into the HR PDB.



From the PDB I see only the users in the PDB scope:

If I change to the root, I see the users valid into all the containers:

Creating a common role

Do the roles obey to the same rules valid for the users?

Yes, they do! So, let’s create a common role with the C## prefix:

It works, but if I try to create a common role into the root container only, I get an error:

And also if I try to create a local role into the root, I can’t:

Note that the error ORA-65049 is different from the ORA-65096 that I’ve got before.

My conclusion is that the clause container of the create role and create user statements doesn’t make sense as you can ONLY create common users and roles into the root container and only local ones into the PDBs.

 Creating a local role

Just as experiment, I’ve tried to see if I can create a local role with container=ALL. It doesn’t work:

So I create the local role with container=current:

Now, from the PDB I can see the two roles I can access, whereas from the root I can see all the roles I’ve defined so far: the common role is available from all the PDBs, the local role only from the db where it has been defined, just like the users.

 Granting object privileges to the roles

From the root I can’t give grants on objects that reside in a PDB since I cannot see them: I need to connect to the PDB and give the grants from there:

Now, if I query CDB_TAB_PRIVS from the root, I see that the grants are given at a local level (con_id=3 and common=N):

 Granting common and local roles to commond and local users

From a PDB, I can grant local roles to local users or common users:

But I can’t grant a common role to a common user with container=all if I’m in a PDB:

To grant the a common role to a common user I can decide either to:

  •  give the grant locally while connected to the PDB:

  •  give the grant commonly while connected to the root:

I can also grant locally both roles and system privileges to common users while connected to the root container: in this case the privileges are applied to the root container only. Finally having the clause container finally starts to make sense:

Verifying the grants

Ok, I’ve given the grants and I’ve never verified if they work, so far.

Let’s try with the select any table privilege I’ve given in the last snippet. I expect C##GOOFY to select any table from the root container and only HR.COUNTRIES and HR.REGIONS on the HR PDB bacause they have been granted through the two roles.

What’s the mess? When I’ve created the user c##goofy, I’ve granted create and alter session without the container=all:

According to the documentation, the grant command uses container=current by default (common=N):

So, I need to give the grants commonly to let c##goofy connect to all the PDBs:

Now I see that the grants give two distinct permissions : one local and the other common.

If I revoke the grants without container clause, actually only the local one is revoked and the user can continue to login. To revoke the grants I would need to check and revoke both local and common privileges.

After the first revoke statement, I can still connect to HR and verify that my select any table privilege doesn’t apply to the PDB as it’s local to the root container:

After that, I want to check the privileges given through the local and common roles.

I expect both users to select from hr.countries and hr.regions since they have been granted indirectly by the roles.

Let’s try the local user first:

Yeah, it works as expected.

Now let’s try the common user:

It also work, so everything is ok.

Common and local grants, why you must pay attention

During the example, I’ve granted the C##COUNTRY_ROLE many times: locally to PDB, locally to the ROOT, commonly. The result is that I’ve flooded the grant table with many entries:

Let’s try to clean things: for sure I don’t need the grant local to the root:

Then I can choose between revoking the common privilege or the local one. Let’s try to remove the local one:

I’ve removed the local one, but I have still the common one (I’m connected to the PDB so the entries from the other containers are not displayed):

I still have access to the tables as expected:

So, you must pay attention to a couple of things:

  • When granting privileges from the root container, keep in mind that container=current is the default even when the grantee or the role granted are common.
  • When revoking the grants with a Multitenant architecture, keep in mind that there is a scope and you may need more than one statement to actually remove the grant from all the scopes.

As always, I look for opinions and suggestions, feel free to comment!



First steps with MySQL Enterprise Monitor 3.0

During the MySQL Connect @ Open World, Oracle has announced the release of MySQL Enterprise Monitor 3.0.

I’ve had the chance to propose a POC on MEM 3.0 to a customer currently relying on MEM 2.3, so we set up a VM to make some tests on it. I want to share my very first experience with it.

The binaries

The binaries you can download from edelivery belong to the “base” 3.0.2 version. But the release 3.0.3 is available since November 1st: in order to get it you must download two patchsets from the My Oracle Support. (Patches & Updates).


  • Patch 17721950: MySQL Enterprise Monitor Service Manager 3.0.3 for Linux x86 (64-bit)
  • Patch 17721960: MySQL Enterprise Monitor Agent 3.0.3 for Linux x86 (64-bit)

So, as it is for Oracle RDBMS, now the new versions are released as patchsets that can be installed from scratch.


The installation

The installation of the new product is as straightforward as it was for the previous release. You can still choose between using an existent MySQL database or a new one created my the installer. The installation steps have not changed at all, so I won’t list them here.

If you’re new to MEM installations, just refer to the official documentation.


New vest

MEM3 comes with a new graphic vest, definitely more “Oracle style” and eye-candy. Globally I have to say that the experience is really improved. The overview page resumes well the overall availability, workload and alerts.


mem3_treeThe new graph browser allows to choose the correspondent object from the left tree-view pane. You can see from the screenshot that now the agent collects data from the system and regroup the items differently, e.g. the filesystems are now separated objects belonging to the server.

New agent behavior

The new MySQL Enterprise Agent brings some benefits comparing to the old one. Now a single agent installation can monitor all database instances on the server and actively discover new ones.
When a new instance is discovered is not monitored by default: an event is raised so you can create an handle that sends you an email that reminds to enable the monitoring for that instance.


Other remarks

The Query Analyzer is now active by default for instances that have the performance_schema enabled.

Many new graphs are displayed by default providing great information on database statistics trends.

The Event Handling is simpler to manage IMO, but the only choices are still sending an email and/or an SNMP trap. I regret that it’s still impossible to take actions like hooking shell scripts or send WS calls.

The other functionalities are still present and basically unchanged.


Oracle have done a very good job in restyling everything. The new Enterprise Monitor dashboard is really responsive and I haven’t found bugs so far. But I have to say that there is still a lack of features that would make it really “enterprise ready”, such as a plugin mechanism that would allow to interact directly with common event management softwares like EM12c, Tivoli, Remedy or CA SM without relying on SNMP only. Also, it would be great to run actions directly when an event raises.

The POC however has been a complete success and we’ll start next week with the definitive migration! 🙂

How many Oracle instances can be consolidated on a single server?

According to Exadata consolidation guide, this is what you can consolidate on Oracle specialized Hardware:

NOTE: The maximum number of database instances per cluster is 512 for Oracle 11g Release 1 and higher. An upper limit of 128 database instances per X2-2 or X3-2 database node and 256 database instances per X2-8 or X3-8 database node is recommended. The actual number of database instances per database node or cluster depends on application workload and their corresponding system resource consumption.


But how many instances are actually beeing consolidated by DBAs from all around the world?

I’ve asked it to the Twitter community

I’ve sent this tweet a couple of weeks ago and I would like to consolidate some replies into a single blog post.


My customer environment however, was NOT a production one. On the production they have 45.

Some replies…




Wissem cores 73 on a production system, 1TB memory!


Chris correctly suggests to give a try to the new 12c consolidation features:


Kevin, as a great expert, already experimented one hundred instances environment:

But Bertrand impresses with his numbers!






Intel platform with 1TB of RAM = Xeon E7, suggests Kevin:




Flashdba has seen 87 instances on a single host, but on a Multi-node RAC: but still huge and complex!





Does this thread of tweets reply to the question? Are you planning to consolidate your Oracle environment? If you have questions about how to plan your consolidation, don’t hesitate to get in touch! 🙂


A good news to start November in a good mood

I’ve just noticed that my room mate at #OOW13 has been recognised as ACE Director.

Even if he was already a world-known performance specialist, this announcement makes me one more time proud to know him. Well deserved Chris! 🙂