Creating – and using – your own services has always been the recommendation. You can connect to a database without a service name, though the instance SID, but this is not what you should do. Each database registers its db_unique_name as a service, and you can use it to connect, but it is always better to create your own application service(s). In multitenant, each PDB registers its name as a service, but the recommendation is still there: create your own services, and connect with your services.
I’ll show in this blog post what happens if you use the PDB name as a service and the standby database registers to the same listener as the primary database. Of course, you can workaround the non-unique service names by registering to different listeners. But this just hides the problem. The main reason to use services is to be independent from physical attributes, so being forced to assign a specific TCP/IP port is not better than using an instance SID.

I have uploaded the the video of my Secret Hacking Session: Oracle X$TRACE, Wait Event Internals and Background Process Communication to my Oracle performance & troubleshooting Youtube channel.

The slides are in Slideshare.

Enjoy!

In the Oracle Database Cloud DBaaS you provision a multitenant database where tablespaces are encrypted. This means that when you unplug/plug the pluggable databases, you also need to export /import the encryption keys. You cannot just copy the wallet because the wallet contains all CDB keys. Usually, you can be guided by the error messages, but this one needs a little explanation and an example.

Here I’ll unplug PDB6 from CDB1 and plug it into CDB2

This is a small demo I did when I’ve found a database password file (orapw) lying around in /tmp with -rw-rw-rw- permissions, to show how this is a bad idea. People think that the orapw file only contains hashes to validate a password given, and forget that it can be used to connect to a remote database without password.

I can easily imagine why the orapwd was there in /tmp. To build a standby database, you need to copy the password file to the standby server. If you don’t have direct access to the oracle user, but only a sudo access for ‘security reasons’, you can’t scp easily. Then you copy the file to /tmp, make it readable by all users, and you can scp with your user.

In this demo I don’t even have access to the host. I’ve only access to connect to a PDB with the SCOTT users, reated with utlsampl.sql, with those additional privileges, a read access on $ORACLE_HOME/dbs:

In the previous post https://blog.dbi-services.com/12c-multitenant-internals-pdb-replay-ddl-for-common-users I’ve done some DDL on a common user to show how this is replayed later for PDBs that were not opened at that time. But what happens when one of the DDL fails on one PDB?

In multitenant, you can create common Users, Roles, and Profiles. You create them in CDB$ROOT, with the CONTAINER=ALL clause (which is optional because it is the only possible value when connected to CDB$ROOT) but they are visible to all containers. As the goal of multitenant is to avoid to duplicate common metadata to all containers, You may think that they are visible through those magic metadata links. But that’s actually wrong: they are simply replicated with a very simple mechanism: the DDL for common objects is replayed into each user PDB.

I’m connected to CDB2’s CDB$ROOT and I have two pluggable databases:

SQL> show pdbs
 
CON_ID CON_NAME OPEN MODE RESTRICTED
------ -------- ---- ---- ----------
2 PDB$SEED READ ONLY NO
3 PDB1 READ WRITE NO
4 PDB2 MOUNTED


PDB1 is opened and PDB2 is closed.

I like that Oracle drops the datafiles from the operating system when we remove them from the database (with drop tablespace or drop pluggable database) because I don’t like to have orphean files remaining in the filesystem. However, to ensure that space is reclaimed, we must be sure that Oracle did not leave a process with this file opened. Linux allows to drop an open file but then drops only the inode. The consequence is that we do not see the file, but space is not reclaimable until the process closes the handle.
Here is a case where I’ve had an issue in 12.2 where plugging a PDB is done in parallel and the parallel processes keep the files opened even if we drop the pluggable database.

I have 1.2 GB free on my filesystem:
SQL> host df -h /u02/oradata
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/ol-root 3.1G 1.9G 1.2G 61% /


More and more we can see crazy queries generated by ORM frameworks or BI query generators. They are build to be easily generated rather than being optimal. Then, the optimizer has to implement more and more transformations to get an efficient execution plan. Here is one new that appeared in Oracle 12cR2: Subquery Elimination when the subquery do not filter any rows.

A semi-join is a join where we do not need to match with all rows, but only one. We write it with an EXISTS subquery or a =ANY or =SOME one, which is equivalent.

A lot of people have asked me to do another run of my Advanced Oracle Troubleshooting training or at least get access to previous recordings – so I decided to geek out over the holiday period, update the material with latest stuff and run one more AOT class in 2018!

The online training will take place on 29 January – 2 February 2018 (Part 1) & 26 February – 2 March 2018 (Part 2).

The latest TOC is below:

• https://blog.tanelpoder.com/files/AOT30_description.pdf

Seminar registration details:

A quick post to show why you should always use LOGTIME=ALL METRICS=Y when using Data Pump. Just look at an example showing the timestamp in front of each line and a message about each task completed by the worker:

15-NOV-17 11:48:32.305: W-5 Processing object type DATABASE_EXPORT/SCHEMA/PROCACT_SCHEMA
15-NOV-17 11:48:34.439: W-13 Completed 28 PROCACT_SCHEMA objects in 1 seconds
15-NOV-17 11:48:34.439: W-13 Completed by worker 1 28 PROCACT_SCHEMA objects in 1 seconds
15-NOV-17 11:48:34.440: W-13 Processing object type DATABASE_EXPORT/SCHEMA/TABLE/TABLE
15-NOV-17 11:48:35.472: W-17 Startup took 70 seconds
15-NOV-17 11:48:35.596: W-18 Startup took 70 seconds
15-NOV-17 11:48:35.719: W-20 Startup took 70 seconds
15-NOV-17 11:48:35.841: W-19 Startup took 70 seconds
15-NOV-17 11:48:43.520: W-5 Completed 1714 TABLE objects in 7 seconds