Today I faced a performance problem caused by a bad cardinality estimation involving a CDB view in a 12.1.0.2 multitenant environment. While solving the problem I did a number of observations that I try to summarize in this blog post. First of all, when checking the execution plan of a query already running for more […]
Purging Unused Triples Is a Never-ending Operation
This is a short post to point out a problem I recently discovered and for which I couldn’t find information online. Hence, in case you hit it, thanks to this short post I hope that you’ll save some time. The documentation describes a procedure you can use to get rid of dangling triples stored in […]
SQL_ADAPTIVE_PLAN_RESOLVED Is Broken
You can use the V$SQL.IS_RESOLVED_ADAPTIVE_PLAN column to know whether the execution plan associated to a child cursor is adaptive or not. Specifically, to know whether the query optimizer selected either an adaptive join method or an adaptive star transformation (notice that it is not set when the hybrid hash distribution is involved). The column takes […]
SPD State Does Not Change If Adaptive Statistics Are Disabled
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 […]
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, […]
Wrong Results Involving INDEX FULL SCAN (MIN/MAX) in 12.1.0.2
One of my customers that recently upgraded to 12c hit a bug (22913528) that I think is good to be aware of. Note that as the title of this post states, the problem only occur in 12.1.0.2. At least, I wasn’t able to reproduce it in any other version. To reproduce it you simply need […]
Oracle Database In-Memory Demos
In the last 14 months I delivered a dozen of presentations covering the In-Memory Column Store. During many of them, I spent most of the time showing the audience several demos. The aim of this post is to share with you the scripts and a recording (MP4) of those demos. Warning about Demos The recordings […]
Online Training Ad: Oracle Database 12c – New Performance Features
On 10 December 2015 I’ll give an online training entitled Oracle Database 12c – New Performance Features. This short post provides key information about it. Description With every new release of Oracle Database, a number of features aimed at improving performance are introduced. It goes without saying that 12.1 is no exception to the rule. […]
Exadata Storage Index Min/Max Optimization
Before discussing the Exadata-specific feature, let’s review what the database engine can do independently of whether Exadata is used. To execute queries containing the min or max functions efficiently, two specific operations are available with B-tree indexes defined on the column referenced in the min or max function. The first, INDEX FULL SCAN (MIN/MAX), is […]