To make upgrades easier, I regularly see people considering disabling query optimizer features by setting the OPTIMIZER_FEATURES_ENABLE initialization parameter to a non-default value. My general opinion about this “habit” is summarized in TOP with the following two sentences:
Changing the default value of the OPTIMIZER_FEATURES_ENABLE initialization parameter is only a short-term workaround. Sooner or later the application should be adapted (optimized) for the new database version.
The issue is that not all new features are (more...)
If you are an attendee of UKOUG Tech14 you have a chance to win a free copy of Expert Oracle SQL by Tony Hasler AND a free copy of Troubleshooting Oracle Performance (2nd edition) by myself.
If you want to know more, click here.
The aim of the STATISTICS COLLECTOR row source operation, which is used in adaptive plans, is to buffer all data produced by its child operation until it is known whether the inflection point is crossed. It goes without saying that buffering requires memory and, therefore, Oracle Database has to limit the amount of memory that can be allocated for that purpose. As a result, in some situations no adaptive plans can be used because according (more...)
With the INMEMORY clause you can specify 4 sub-clauses:
- The MEMCOMPRESS clause specifies whether and how compression is used
- The PRIORITY clause specifies the priority (“order”) in which the segments are loaded when the IMCS is populated
- The DISTRIBUTE clause specifies how data is distributed across RAC instances
- The DUPLICATE clause specifies whether and how data is duplicated across RAC instances
The aim of this post is not to describe these attribues in detail. Instead, (more...)
I strive to keep the number non-technical posts on this blog to the minimum. However, there are days when a non-technical post has to be written. This is one of such days.
Oracle Corporation, concerned about legal and ethical issues, not only provides to its employees a document entitled Code of Ethics and Business Conduct, but also expects that every employee adheres with the standards that the document sets. For the purpose of (more...)
The aim of this post is not to explain how the APPROX_COUNT_DISTINCT function works (you find basic information in the documentation and in this post written by Luca Canali), but to show you the results of a test case I run to assess how well it works.
Here’s what I did…
I created a table with several numerical columns (the name of the column shows how many distinct values it contains), loaded 100 million (more...)
Every new Oracle Database patch introduces not only documented features, but also undocumented ones. In this short post I would like to provide information about an enhancement of the RESULT_CACHE hint.
According the documentation, the RESULT_CACHE hint has no parameter. But, as of 22.214.171.124, at least the SNAPSHOT parameter is supported. Its purpose is to specify how much time (in seconds) after the creation the result cache entry has to (more...)
This is just a short post to point out that the downloadable files are available here. You can download either a ZIP or a TAR file containing all files, or single files.
Since every file has its own URL, you can also directly executed them in SQL*Plus. For example:
I’m sorry for the delay!
Several people asked me how much I changed in the second edition. The short answer is… A LOT.
The main goals set for the revision of the book were the following:
- Add content about Oracle Database 11g Release 2 and Oracle Database 12c Release 1.
- Remove content about Oracle9i and Oracle Database 10g Release 1.
- Add content that was “missing” in the first edition (for example, features like hierarchical profiler, active session history, AWR and (more...)
Few days ago the second edition of Troubleshooting Oracle Performance was finally published. Today, I updated the pages on this site that provide information about the book. It goes without saying that the new pages cover the second edition. Hence, from here you can access the description, the table of contents, the forewords written by Jonathan Lewis and Cary Millsap, as well as a page with some errata. Yes, as for the first edition, (more...)