Query Optimizer

The 11th and 12th of December and, therefore, the CBO Days in Zurich are approaching. Given the high quality of the speakers that accepted my invitation and the number of people that decided to attend the event, in my opinion it will be a blast! By the way, if you are interested in attending the event, do not wait any longer. In fact, from the 80 available seats, 75 are taken.

Here is a preview of the agenda:

Tuesday 11th December

The company I work for, Trivadis, is very pleased to organize, the 11th and 12th of December, an outstanding seminar with top guest speakers in Zurich. This year’s focus will be on the Oracle query optimizer, also known as a cost-based optimizer (CBO).

The query optimizer is not only one of the most complex pieces of software that constitutes the Oracle kernel; it is also one of the most unappreciated. Why? To make the best and most efficient use of the query optimizer, you definitely need to understand how it works. This is exactly what we are aiming for at the CBO Days.

Enjoy the two days with:
- Jonathan Lewis, JL Computer Consultancy (GB)
- Jože Senegačnik, DbProf (SI)
- Maria Colgan, Optimizer product manager, Oracle Corporation (USA)
- Mohamed Zait, Optimizer chief developer, Oracle Corporation (USA)
- Randolf Geist, Freelance (DE)
- Christian Antognini, Trivadis (CH)

Most execution plans can be interpreted by following few basic rules (in TOP, Chapter 6, I provide such a list of rules). Nevertheless, there are some special cases. One of them is when an index scan, in addition to the access predicate, has a filter predicate applying a subquery.

The following execution plan, taken from Enterprise Manager 11.2, is an example (click on the image to increase its size):

Notes:

The 31st of January and 1st of February 2012 I will present a 2-day seminar about the Oracle query optimizer in Ballerup (DK). The event is organized by Miracle A/S. The content, which is based on the chapters 2, 4, 5, 6, 9 and 10 of my book, is the following:

Challenges and Chances of the 11g Query Optimizer is the name of a presentation I gave at several events (e.g. Trivadis Performance Days, Oracle OpenWorld, DOAG Konferenz, UKOUG Conference) throughout 2011. Its abstract is the following:

With every new release, the query optimizer is enhanced. Oracle Database 11g Release 1 and Release 2 are no exception to the rule. Specifically, they introduce key improvements in the following areas: indexing, optimization techniques, object statistics and plan stability. The aim of this presentation is to review the new features from a practical point of view as well as to point out challenges related to them. In other words, to let you know what you can expect from the query optimizer when you upgrade to Oracle Database 11g.

The STATISTICS_LEVEL parameter controls a bunch of features. In addition to the documentation, also the V$STATISTICS_LEVEL view provides a list of the ones it controls.

At page 189 of TOP I wrote the following piece of text:

In summary, with the initialization parameter optimizer_secure_view_merging set to TRUE, the query optimizer checks whether view merging could lead to security issues. If this is the case, no view merging will be performed, and performance could be suboptimal as a result. For this reason, if you are not using views for security purposes, it is better to set this initialization parameter to FALSE.

What I didn’t consider when I wrote it, it is the implication of predicate move-around related to Virtual Private Database (VPD). In fact, as described in the documentation, that parameter controls view merging as well as predicate move-around.

At page 383 of my book I wrote the following sentence (BTW, the same information is also provided by Table 9-3 at page 381):

With B-tree indexes, IS NULL conditions can be applied only through composite B-tree indexes when several SQL conditions are applied and at least one of them is not based on IS NULL or an inequality.

The text continues by showing the following examples (notice that in both cases the IS NULL predicate is applied through an access predicate):

As of 11.2.0.2 a new package, DBMS_AUTO_SQLTUNE, is available for accessing and configuring Automatic SQL Tuning. The package provides three features:

Execution of the Automatic SQL Tuning task (EXECUTE_AUTO_TUNING_TASK)
Generation of a report showing the output generated by the Automatic SQL Tuning tasks (REPORT_AUTO_TUNING_TASK)
Configuration of the Automatic SQL Tuning parameters (SET_AUTO_TUNING_TASK_PARAMETER)

In this post I would like to [...]

When I started writing the series of posts about Exadata Storage Server and the query optimizer, I didn’t expect to write more than three posts (part 1, part 2, part 3). Of course, things change. Hence, here is part 4 to cover a couple of things that I learned in the next couple of months.
In [...]