Get information about Cursor Sharing for a SQL_ID

Yesterday I’ve got a weird problem with Adaptive Cursor Sharing. I’m not sure yet about the issue, but it seems to be related to cursor sharing histograms. Hopefully one day I will blog about what I’ve learnt from this experience.

To better monitor the problem on that specific query, I’ve prepared this script (tested on

The result is something similar (in my case it has 26 child cursors):

It’s a quick way to get the relevant information in a single result.

Off course, if you need deeper details, you should consider something more powerful like SQLd360 from Mauro Pagano.

Credits: I’ve got the unpivot idea (and copied that part of the code) from this post by Timur Akhmadeev.


It’s confirmed. Standard Edition and Standard Edition One are dead.

The first voices came on July 3rd, 2015.

After many years of existence, Standard Edition and Standard Edition One will no longer be part of the Oracle Database Edition portfolio.

The short history

Standard Edition has been for longtime the “stepbrother” of Enterprise Edition, with less features, no options, but cheaper than EE. I can’t remember when SE has been released. It was before 2000s, I guess.

In 2003, Oracle released 10gR1. Many new features as been released for EE only, but:

– RAC as been included as part of Standard Edition

– Standard Edition One has been released, with an even lower price and “almost” the same features of Standard Edition.

For a few years, customers had the possibility to get huge savings (but many compromises) by choosing the cheaper editions.

SE ONE: just two sockets, but with today’s 18-core processors, the possibility to run Oracle on 36 cores (or more?) for less than 12k of licenses.

SE: up to four sockets and the possibility to run on either 72 core servers or RAC composed by a total of 72 cores (max 4 nodes) for less than the price of a 4-core Enterprise Edition deployement.

In 2014, for the first time, Oracle released a new Database version ( where  Standard Edition and SE One were not immediately available.

For months, customers asked: “When will the Oracle SE be available?”

Now the big announcement: SE and SE One will no longer exist. With, there’s a new Edition: Oracle Database Standard Edition 2.

You can find more information here:


Some highlights

– SE One will no longer exist

– SE is replaced by SE Two that has a limitation of 2 sockets

– SE Two still has RAC feature, with a maximum of two single-socket servers.

– Customers with SE on 4 socket nodes (or clusters) will need to migrate to 2 socket nodes (or clusters)

– Customers with SE One should definitely be prepared to spend some money to upgrade to SE Two, which comes at the same price of the old Standard Edition. ($17,500 per socket).

– the smallest amount of NUP licenses when licensing per named users has been increased to 10 (it was 5 with SE and SE One).

– Each SE2 Database can run max 16 user threads (in RAC, max 8 per instance). This is limited by the database Resource Manager. It does not prevent customers from using all the cores, in case they want to deploy many databases per server.


So, finally, less scalability for the same pricetag.

Other bloggers have already written about the behaviour of SE2. The best blog post is IMO from Franck Pachot.



Block Change Tracking and Duplicate: avoid ORA-19755

If you use Block Change Tracking on your production database and try to duplicate it, you there are good possibilities that you will encounter this error:

The problem is caused by the block change tracking file entry that exists in the target controlfile, but Oracle can’t find the file because the directory structure on the auxiliary server changes.

After the restore and recovery of the auxiliary database, the duplicate process tries to open the DB but the bct file doesn’t exist and the error is thrown.

If you do a quick google search you will find several workarounds:

  • disable the block change tracking after you get the error and manually open the auxiliary instance (this prevent the possibility to get the duplicate outcome from the rman return code)
  • disable the BCT on the target before running the duplicate (this forces your incremental backups to read all your target database!)
  • Richard Harrison proposed another workaround, you can read more about it here.

There is another workaround that I like more (and that you can also find as comment in Richard’s post):

  • Disable the Block Change Tracking on the auxiliary while it’s doing the restore/recovery (in mounted status)

(This solutions isn’t coming from me, but as far as I know, the father of this solution is a colleague working at Trivadis.)

You can easily fork a process before running the duplicate command that:

  • loops and checks the auxiliary instance status
  • run the disable as soon as the auxiliary is mounted

I’ve worked out this script that does the job:

Run it  just before the duplicate! e.g.



SQL Plan Directives: they’re always good… except when they’re bad!

The new Oracle 12c optimizer adaptive features are just great and work well out of the box in most cases.

Recently, however,  I’ve experienced my very first problem with SQL Plan Directives migrating a database to 12c, so I would like to share it.

Disclaimer 1: this is a specific problem that I found on ONE system. My solution may not fit with your environment, don’t use it if you are not sure about what you’re doing!

Disclaimer 2: despite I had this problem with a single SPD, I like adaptive features and I encourage to use them!!

Problem: a query takes a sub-second in 11gR2, in 12c it takes 12 seconds or more.

V_TAB_PROP is a very simple view. It just selects a central table “TAB” and then takes different properties by joining  a property table “TAB_PROP”.

To do that, it does 11 joins on the same property table.

On the property table, TAB_PROP_ID and PROP_ID are unique (they compose the pk), so nested loops and index unique scans are the best way to get this data.
The table is 1500Mb big and the index 1000Mb.

This was the plan in 11g:

In 12c, the plan switches to adaptive, and half of the joins are converted to hash joins / full table scans:

However, the inflection point is never reached. The execution keeps the default plan that has half of the joins HJ and the other half NL.

The problem in this case is the SQL Directive. Why?

There are to many distinct values for TAB_ID and the data is very skewed.

The histogram on that column is OK and it always leads to the correct plan (with the adaptive features disabled).
But there are still some “minor” misestimates, and the optimizer sometimes decides to create a SQL Plan directive:

The Directive instructs the optimizer to do a dynamic sampling, but with a such big and skewed table this is not ok, so the Dynamic sampling result is worse than using the histogram. I can check it by simplifying the query to just one join:

What’s the fix?

I’ve tried to drop the directive first, but it reappears as soon as there are new misestimates.
The best solution in my case has been to disable the directive, an operation that can be done easily with the DBMS_SPD package:

I did this on a QAS environment.
Because the production system is not migrated to 12c yet, it’s wise to import these disabled directives in production before the optimizer creates and enables them.

Off course, the directives can’t be created for objects that do not exist, the import  has to be done after the objects migrate to the 12c version.

Because the SQL Plan Directives are tied to specific objects and not specific queries, they can fix many statements at once, but in case like this one, they can compromise several statements!

Monitoring the creation of new directives is an important task as it may indicate misestimates/lack of statistics on one side or execution plan changes on the other one.

Moving Clusterware Interconnect from single NIC/Bond to HAIP

Very recently I had to configure a customer’s RAC private interconnect from bonding to HAIP to get benefit of both NICs.

So I would like to recap here what the hypothetic steps would be if you need to do the same.

In this example I’ll switch from a single-NIC interconnect (eth1) rather than from a bond configuration, so if you are familiar with the RAC Attack! environment you can try to put everything in place on your own.

First, you need to plan the new network configuration in advance, keeping in mind that there are a couple of important restrictions:

  1. Your interconnect interface naming must be uniform on all nodes in the cluster. The interconnect uses the interface name in its configuration and it doesn’t support different names on different hosts
  2. You must bind the different private interconnect interfaces in different subnets (see Note: 1481481.1 – 11gR2 CSS Terminates/Node Eviction After Unplugging one Network Cable in Redundant Interconnect Environment if you need an explanation)



The RAC Attack book uses one interface per node for the interconnect (eth1, using network

To make things a little more complex, we’ll not use the eth1 in the new HAIP configuration, so we’ll test also the deletion of the old interface.

What you need to do is add two new interfaces (host only in your virtualbox) and configure them as eth2 and eth3, e.g. in networks and


modify /var/named/racattack in order to use the new addresses (RAC doesn’t care about logical names, it’s just for our convenience):

add also the reverse lookup in


restart  named on the first node and check that both nodes can ping all the names correctly:

check the nodes that compose the cluster:

on all nodes, make a copy of the gpnp profile.xml (just in case, the oifcfg tool does the copy automatically)

List the available networks:

Get the current ip configuration for the interconnect:

one one node only, set the new interconnect interfaces:

check that the other nodes has received the new configuration:

Before deleting the old interface, it would be sensible to stop your cluster resources (in some cases, one of the nodes may be evicted), in any case the cluster must be restarted completely in order to get the new interfaces working.

Note: having three interfaces in a HAIP interconnect is perfectly working, HAIP works from 2 to 4 interfaces. I’m showing how to delete eth1 just for information!! 🙂

on all nodes, shutdown the CRS:

Now you can disable the old interface:

and modify the parameter ONBOOT=no inside the configuration script of eth1 interface.

Start the cluster again:

And check that the resources are up & running:


 Testing the high availability

Disconnect cable from one of the two interfaces (virtually if you’re in virtualbox 🙂 )

Pay attention at the NO-CARRIER status (in eth2 in this example):

check that the CRS is still up & running:


The virtual interface eth2:1 as failed over on the second interface as eth3:2


After the cable is reconnected, the virtual interface is back on eth2:


Further information

For this post I’ve used a RAC version 11.2, but RAC 12c use the very same procedure.

You can discover more here about HAIP: 

And here about how to set it (beside this post!):




Removing passwords from Oracle scripts: Wallets and Proxy Users

Very often I encounter customers that include Oracle account passwords in their scripts in order to connect to the database.
For DBAs, sometimes things are
easier when they run scripts locally using the oracle account, since the “connect / as sysdba” usually do the job, even with some security concerns. But what if we need other users or we need to connect remotely?
Since longtime Oracle supplies secure wallets and the proxy authentication. Let’s see what they are and how to use them.

Secure Wallet
Secure wallets are managed through the tool mkstore. They allow to store a username and password in a secure wallet accessible only by its owner. The wallet is then accessed by the Oracle Client to connect to a remote database, meaning that you DON’T HAVE to specify any username and password!

Let’s see how to implement this the quick way:

Create a directory that will contain your wallet:

Create the wallet, use an arbitrary complex password to protect it:

Immagine that you’ve a user created with a very complex password:

Then you need to insert these credentials, including the connect string, into the wallet.

Keep in mind that you can have multiple credentials in the wallet for different remote descriptors (connect strings), but if you want many credentials for the very same connect string you need to create different wallets in different directories.

Now you need to tell your Oracle Client to use that wallet by using the wallet_location parameter in your sqlnet.ora, so you need to have a private TNS_ADMIN:

If everything’s alright, you should be able to connect to the database PROD as the batch user, without specifying any username or password.

Attention: when mkstore modifies the wallet, only the clients with the same or above versions will be able to access the wallet, so if you access your wallet with a 11g client you shouldn’t modify the wallet with a 12c version of mkstore. This is not documented by Oracle, but you can infer it from different “not a bug” entries on MOS 🙂

Proxy Users
You can push things a little farther, and hook your wallet with a proxy user, in order to connect to arbitrary users. That’s it, a proxy user is entitled to connect to the database on behalf of other users. In this example, we’ll see how, through the batch account, we can connect as OE, SH or HR:

Now I can specify with which user I want to work on the DB, connect to it through the batch account, without specifying the password thanks to the wallet:


See how it’s easy? But don’t forget to keep your wallet secure using unix/windows permissions!

Oracle Instances and real memory consumption on Linux and Solaris

There’s a way to know the REAL memory usage by Oracle Instance, including all connecting processes and using the shell rather than a connection to oracle?

The short answer is “I think so” 🙂

Summing up RSS column from ps output, is not reliable because Linux uses a copy-on-write on process forks and also doesn’t take into account correctly the shared memory and other shared allocations.

I’ve come across this post on Pythian’s Blog from Marc Billette.

While it seems good I’ve had discording results depending on platform and release.

Instead, I’ve tried to create a shell snippet that always uses pmap but works differently and SEEMS to work correctly on Linux ans Solaris.

Basically, using the pmap script I get a lot of information about the different memory areas allocated to the process:


Initially I’ve tried to decode correctly the different kinds of memory the same way other scripts I’ve found online do:

but finally the ADDRESS is the same from different processes when the memory area is shared, so my script now just get a unique line for each address and sums up the memory size (not the rss one!):

This should give the total virtual memory allocated by the different Oracle instances.

The results I get are plausible both on Linux and Solaris.


If you find any error let me know and I’ll fix the script!


Regular TNS-12508 critical alerts in EM12c

Yesterday I’ve come across a small request from a customer.
They were receiving REGULARLY critical alerts in EM12c from some listeners due to error TNS-12508.

The facts:

  • only 10g listeners were affected
  • every day, only one occurrence of the error and always at the same time on a named host
  • no apparent correlations between times on different hosts

I’ve analyzed the log to see the error.


Notice that after the error there are two requests: show log_directory and show trc_directory.
So I’ve supposed that it’s an additional request failing on 10g listeners but not on 11g listeners.
The “help” command of 10g and 11g releases shows that the two releases have some different commands. One of them is “show oracle_home” that has been introduced in 11g.

  • First I’ve searched for scheduled scripts (the customer literally have a huge library of scripts run against the databases to automate maintenance tasks)
  • Then I’ve asked to the team that manages an automatic discovery tool that feeds the CMDB
  • Finally, I’ve come across this note on Metalink that explain the error:

Repetitive TNS-12508 Errors logged for a listener target after upgrade to DB plugin or higher (Doc ID 1596633.1)

I’ve applied the change to the metrics in EM12c to ignore the error for 10g listeners.


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!



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! 🙂