Script: Finding Session With Downgraded Parallel Execution

I was working with the data warehouse team at a customer site and at some point we realized that some parallel executions are not getting enough resources (downgraded).

Not getting enough parallel processes in such a complex environment is really bad. That means that since everybody is hogging the CPU, some sessions will not be able to complete inside the night ETL time frame. If that happens – some ETLs will go on into the (more...)

Explicit Semantic Analysis setup using SQL and PL/SQL

In my previous blog post I introduced the new Explicit Semantic Analysis (ESA) algorithm and gave an example of how you can build an ESA model and use it. Check out this link for that blog post.

In this blog post I will show you how you can manually create an ESA model. The reason that I'm showing you this way is that the workflow (in ODMr and it's scheduler) may not be for everyone. (more...)

Oracle Diagnostic Queries

It’s always a challenge when you want to build your own Oracle SQL Tools. I was asked how you could synchronize multiple cursors into a single source. The answer is quite simple, you write an Oracle object type to represent a record structure, an Oracle list of the record structure, and a stored function to return the list of the record structure.

For this example, you create the following table_struct object type and a table_list (more...)

Explicit Semantic Analysis in Oracle 12.2c Database

A new Oracle Data Mining algorithm in the Oracle 12.2c Database is called Explicit Semantic Analysis.

[The following examples are built using Oracle Data Miner 4.2 (SQL Developer 4.2) and the Oracle 12.2 Database cloud service (extreme edition) ]

The Explicit Semantic Analysis algorithm is an unsupervised algorithm used for feature extraction. ESA does not discover latent features but instead uses explicit features based on an existing knowledge base. There (more...)

A Recipe for Summoning the RBO Monster (even in Oracle 12c): On Delete Cascade, Function-Based Index and Missing Table Statistics

The last version of Oracle in which CHOOSE was officially supported as an OPTIMIZER_MODE parameter value was 9.2.
This is what the documentation of Oracle 9.2 says about it:

The optimizer chooses between a cost-based approach and a rule-based approach based on whether statistics are available.
If the data dictionary contains statistics for at least one of the accessed tables, then the optimizer uses a cost-based approach and optimizes with a goal (more...)

Inserting data in SQL*Plus correctly

When inserting data into the database, it is occasionally forgotten (especially by English-speakers) that we need to take steps to ensure we are inserting data correctly and without unexpected character translation.

For example, in SQL*Plus we need to ensure we set the NLS_LANG environment variable to the correct setting for our database before we initiate SQL*Plus.

Here’s a quick example showing what can go wrong:

[oracle@ORA122 ~]$ echo $NLS_LANG

[oracle@ORA122 ~]$ sqlplus neil/neil
SQL*Plus: Release  (more...)

Scanning an Index

The internet is full of information about indexes, and for a reason. Indexes in a database is probably the most important performance related topic. There are so many cases, properties, and different ways to use indexes that there is simply a lot to write about. In this post I’d like to talk about a specific … Continue reading Scanning an Index

Auditing Oracle Data Mining model usage

In a previous blog post I talked about how you can rename and comment your Oracle Data Mining models. This is to allow you to easily to see and understand the intended use of the data mining model.

Another feature available to you is to audit the usage of the the data mining models. As your data mining environment grows to many 10s or more typically 100s of models, you will need to have some (more...)

The “Control Freak Trigger” Design Pattern

Suppose that every time we add records into the T1 table we have to do some additional stuff.
One option to implement this is by using an AFTER INSERT trigger that will perform this additional stuff, but I really dislike this option (mainly because the code becomes hidden in a way, and there may be a negative impact on performance).
I prefer writing a procedure that inserts the records into T1 and performs this additional (more...)

Renaming & Commenting Oracle Data Mining Models

As your company evolves with their data mining projects, the number of models produced and in use in production will increase dramatically.

Care needs to be taken when it comes to managing these. This includes using meaningful names, adding descriptions of what the model is about or for, and being able to track their usage, etc.

I will look at tracking the usage of the models in another blog post, but the following gives examples (more...)

#UKOUG_Tech16: Ranges, Ranges Everywhere

I presented this topic on at Tech 16 on Monday afternoon. The latest version is on the Tech 16 website and on Thanks to the organisers, staff, presenters and delegates who made this a great conference and a wonderful experience!

#UKOUG_Tech16: Advanced Row Pattern Matching

I presented this topic on Super Sunday. The latest version is now on the Tech16 site and on

Evaluating Cluster Dispersion in Oracle Data Mining

When working with the Clustering algorithms, and particularly k-Means, in the Oracle Data Miner tool there is no way of seeing how compact or dispersed the data is within a cluster.

There are a number of measures typically used in various tools and algorithms, but with Oracle Data Miner we are not presented with any of this information.

But if we flip from using the Oracle Data Miner tool to using SQL we can get (more...)

SQL Developer: Quick Outline with SQL statements

Most of you probably know the "Quick Outline" function you have inside the SQL Developer.
It helps you to easily jump between different functions/procedures inside a package.

My colleague Holger told me about a bug in SQL Developer 3.x where you could use the "Outline" view with normal SQL files, too. Unfortunately in version 4 it didn't work anymore. So he stayed with version 3 for a long while. Otherwise he would had to (more...)

Answer with SQL: How many weekdays a year?

I'm a big fan of generating data with dual, using a perk of the connect by syntax.

I think Tom Kyte was the originator of this technique. It's not necessarily the fastest method, but it's super convenient - no table required.

Today I wanted to know how many weekdays a year, so I defined 365 rows on the fly using sysdate to turn these into each day of the year. Then I ran a simple (more...)

Tablespaces verkleinern (TEMP, USER_TS, ORA-03297)

Die Select-Statements in diesem Blogpost habe ich von anderen Webseiten kopiert. Daher ist dieser Beitrag eher als Zusammenfassung unterschiedlicher Lösungsversuche zu sehen und dient mir als schnelle Hilfe bei der Verkleinerung eines zu großen Tablespaces. Schaut euch die Quellen an, die sehr viel detaillierter auf die jeweiligen Probleme eingehen.

Wer kennt nicht die Situation? Der DBA ruft an und meint der TEMP Tablespace verbraucht mehrere hundert Gigabyte an Speicher.

Was ist in solch einer (more...)

Friday Philosophy – Your Experience can Keep You Ignorant

This week I was in an excellent presentation by Kerry Osborne about Outlines, SQL profiles, SQL patches and SQL Baselines. I’ve used three of those features in anger but when I looked at SQL Patches I just could not understand why you would use them – they looked to me like a very limited version of SQL Profiles.

There is a prize for spotting Kerry without a baseball cap

There is a prize for spotting Kerry without a baseball cap

So I asked Kerry about it (more...)

#DOAG2016: Ranges, Ranges Everywhere!

Today I did my second presentation at DOAG2016. It was at 9:00 so I got to sleep in ;) The room was huge but there were enough people that I didn’t feel too lonely. The room and the technical help were top notch, and again there were questions at just the right time to remind me […]

#DOAG2016: Advanced Row Pattern Matching

DOAG2016 started today at 8:30, and I did too. There were so many great presentations at the same time as mine, I was surprised and pleased to get a nice audience.

Using the Identity column for Oracle Data Miner

If you are a user of the Oracle Data Miner tool (the workflow data mining tool that is part of SQL Developer), then you will have noticed that for many of the algorithms you can specify a Case Id attribute along with, say, the target attribute.


The idea is that you have one attribute that is a unique identifier for each case record. This may or may not be the case in your data model (more...)