The aim of this post is to point out an issue (bug?) that I recently discovered. But, before talking about it, I need to go through a rather long introduction about the state of SQL plan directive (SPD). As of version 12.1.0.2, an SPD has two state information. You can see both of them through […]
The APPROX_MEDIAN Function – A Test Case
The aim of this post is not to explain how the APPROX_MEDIAN function works (you find basic information in the documentation) but to show you the results of a test case I ran to assess how well it works. Here’s what I did… I started in the Oracle Database Public Cloud an instance of version […]
Activating and Deactivating Performance Feedback
Performance feedback is one of the adaptive query optimizer features introduced in Oracle Database 12c. The aim of this short post isn’t to explain how it works, but to simply warn you about a buggy behavior in its configuration. The parameters that control performance feedback in 12c are the following: OPTIMIZER_ADAPTIVE_FEATURES (12.1 only): if set […]
Offline Analysis of ASH Data with ASHDUMP
From time to time, it happens to me to carry out offline analyses of ASH data. For that, I mean to analyze the ASH data without having access to the database instance that generated it. For that purpose, Oracle Database provides the possibility to dump the content of the ASH buffer as well as information […]
Scripts to Download Oracle Database 12c Release 2 Documentation
In the past (here, here and here) I already shared with you the scripts I use to download the Oracle Database documentation. The aim of this short post is to reference the script I just wrote for the latest version: 12c Release 2. download122.sh Happy downloading as well as happy reading! Update 2018-02-27: new version […]
Adaptive Query Optimization: Backport of 12.2 Configuration in 12.1.0.2
I finally managed to install and test patch 22652097 (PROVIDE SEPARATE CONTROLS FOR ADAPTIVE PLANS AND ADAPTIVE STATISTICS FEATURES). Actually, I installed and tested two patches. The first was installed on top of “Oracle Database Patch 23054246 – Database Patch Set Update 12.1.0.2.160719” (from now on, 12.1.0.2.160719 PSU). The second was installed on top of […]
Ad – Oracle Database 12c Release 1 and 2: New Performance Features
In the past I gave a number of 1-day seminars about the new performance features available in Oracle Database 12c Release 1. On the 22nd of February, for the first time, I’ll give an updated version of that seminar with content about both Release 1 and Release 2. Note that because there is more content, […]
Initialization Parameters Set at the PDB Level Are Not Always Honored
Before describing the issue that lead to this post, let’s shortly review how the handling of initialization parameters works in a multitenant environment. Initialization parameters exist at both the CDB level and the PDB level. This is a critical feature because it wouldn’t be acceptable to use the same set of initialization parameters for all […]
Approximate Aggregate Transformation (AAT)
There are situations where approximate results are superior than exact results. Typically, this is the case when two conditions are met. First, when the time and/or resources needed to produce exact results are much higher than for approximate results. Second, when approximate results are good enough. Approximate results are for example superior in case of […]
Trace Files Split in Multiple Parts
Last January, in the following tweet, I pointed out that the documentation vaguely mentions that a trace file may be split into several files. Did you successfully tested the new MAX_DUMP_FILE_SIZE behavior? If yes, which version/OS?https://t.co/4F9f9wsT95 pic.twitter.com/X2Y7FNf1HG — Christian Antognini (@ChrisAntognini) January 20, 2016 As a follow-up, few days later Jonathan Lewis published a post […]