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May 2018

demystifying and wrapping the oracle cloud APIs with Python

As an oracle DBA you might have to deal with REST API, especially when working with the cloud. The purpose of this post is to demystify the REST API usage from a DBA point of view. Let’s take an example and write a Python wrapper to automate the Instance creation in the Oracle Database Cloud Service.

The instance creation can be done manually using the Web Interface that way:

Which Bitnami service to choose in the Oracle Cloud Infrastructure?

In the Oracle Cloud PaaS you have a marketplace where you can choose your service. Some are packaged from Bitnami and available on multiple OS. My first idea is that in PaaS you do not care about the OS. But Oracle Cloud has this very nice feature where you still have full access to the OS, as root, even in PaaS. Then, you choose the Linux distribution of your preference. Except if performance is different. They run on different Linux kernels. Is Oracle Linux Unbreakable Kernel more efficient?

We need to compare with relevant and reliable measures. And for that I’ve created a Postgres service and used Kevin Closson SLOB method, as I’m a lucky beta tester for pgio. I’ll post later about the creation of the Postgres service in the Oracle Cloud.

This is GDPR Reality

How many updated policies for use of personal data did you sign off the last couple days? As I had observed the EU procrastinating on their compliance for General Data Protection Regulations, (GDPR) until December of 2016, (it went into effect in April, 2014 with a deadline in the EU of December, 2016) I wasn’t surprised that we’re seeing a flurry of requests to sign off on data usage this week. The deadline is tomorrow, May 25th for non-EU and as expected, here we are.

A re-introduction to the vagrant-builder suite for database installation

In a blogpost introducing the vagrant builder suite I explained what the suite could do, and the principal use, to automate the installation of the Oracle database software and the creation of a database on a virtual machine using vagrant together with ansible and virtual box.

This blogpost shows how to use that suite for automating the installation of the Oracle database software and the creation of a database on a linux server directly, with only the use of ansible without vagrant and virtualbox.

Show parameter

Just a quick little tip for Friday afternoon.

If you use the “show parameter” or “show spparameter” commands from SQL*Plus you’ve probably noticed that the parameter value may be too long for the defined output column, and even the parameter name may occasionally be too long. For example (from

Hybrid Columnar Compression in 12.2 – nice new feature

Oracle 12.2 introduced an interesting optimisation for Hybrid Columnar Compression (HCC). Until 12.2 you had to use direct path inserts into HCC compressed segments for data to be actually compressed. If you didn’t use a direct path insert you would still succeed in entering data into the segment, however your newly inserted data was not HCC compressed. There is no error message or other warning telling you about that, which can lead to surprises for the unaware.

My friend and colleague Nick has pointed out that the official HCC white paper states – somewhat hidden – that this requirement is no longer as strict in 12.2. I haven’t managed to find the document Nick pointed out, but a quick search using my favourite retrieval engine unearthed the updated version for 18c.

Postgres, the fsync() issue, and ‘pgio’ (the SLOB method for PostgreSQL)

That’s a long blog post title, which is actually just a good pretext to play with Kevin Closson SLOB method for PostgreSQL: pgio
I use the beta version of pgio here. If you want to read more about it, you can start on If you are used to the SLOB for Oracle ( you will quickly understand the ‘why’ and ‘how’ of pgio.

ADWC – System and session settings (DWCS lockdown profile)

The Autonomous Data Warehouse Cloud service is a PaaS managed service where we have a PDB and an ADMIN user which has most of the system privileges. For example, we have the privilege to change initialization parameters:
SQL> select * from dba_sys_privs where grantee=user and privilege like 'ALTER S%';
------- --------- ------------ ------ ---------

Still, not everything is allowed for several reasons: ensure that we cannot break the Oracle managed CDB and force us to use only the features allowed in the ‘autonomous’ service. This is limited with a lockdown profile:
SQL> show parameter pdb_lockdown
------------ ------ -----
pdb_lockdown string DWCS

Missing Audit

Here’s a detail I discovered a long time ago – and rediscovered very recently: it’s possible to delete data from a table which is subject to audit without the delete being audited. I think the circumstances where it would matter are a little peculiar, and I’ve rarely seen systems that use the basic Oracle audit feature anyway, but this may solve a puzzle for someone, somewhere, someday.

The anomaly appears if you create a referential integrity constraint as “on delete cascade”. A delete from the parent table will automatically (pre-)delete matching rows from the child table but the delete on the child table will not be audited. Here’s a demonstration script – note that you will need to have set the parameter audit_trail to ‘DB’ to prove the point.

Sneak Preview of pgio (The SLOB Method for PostgreSQL) Part IV: How To Reduce The Amount of Memory In The Linux Page Cache For Testing Purposes.

I hope these sneak peeks are of interest…

PostgreSQL and Buffered I/O

PostgreSQL uses buffered I/O. If you want to test your storage subsystem capabilities with database physical I/O you have to get the OS page cache “out of the way”–unless you want to load really large test data sets.

Although pgio (the SLOB Method for PostgreSQL) is still in Beta, I’d like to show this example of the tool I provide for users to make a really large RAM system into an effectively smaller RAM system.

Linux Huge Pages

Memory allocated to huge pages is completely cordoned off unless a process allocates some IPC shared memory (shmget(1)).  The pgio kit comes with a simple tools called which leverages this quality of huge pages in order to draw down available memory so that one can test physical I/O with a database size that is quite smaller than the amount of physical memory in the database host.