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Performance tuning

Oracle 19c Automatic Indexing: CBO Incorrectly Using Auto Indexes Part II ( Sleepwalk)

As I discussed in Part I of this series, problems and inconsistencies can appear between what the Automatic Indexing processing thinks will happen with newly created Automatic Indexing and what actually happens in other database sessions. This is because the Automatic Indexing process session uses a much higher degree of Dynamic Sampling (Level=11) than other […]

Oracle 19c Automatic Indexing: Data Skew Part II (Everything’s Alright)

In my previous post, I discussed an example with data skew, in which the Automatic Indexing process created a new index, but somehow the CBO when using the index estimated the correct cardinality estimate even though no histograms were explicitly calculated. In this post I’ll answer HOW this achieved by the CBO. Get some idea […]

Oracle 19c Automatic Indexing: Data Skew Part I (A Saucerful of Secrets)

When it comes to Automatic Indexes, things can become particularly interesting when dealing with data skew (meaning that some columns values are much less common than other column values). The next series of blog posts will look at a number of different scenarios in relation to how Automatic Indexing works with data that is skewed […]

Oracle 19c Automatic Indexing: Poor Data Clustering With Autonomous Databases Part III (Star)

In Part I we looked at a scenario where an index was deemed to be too inefficient for Automatic Indexing to create a VALID index, because of the poor clustering of data within the table. In Part II we improved the data clustering but the previous SQLs could still not generate a new Automatic Index […]

Oracle 19c Automatic Indexing: Poor Data Clustering With Autonomous Databases Part II (Wild Is The Wind)

  In my previous post, I discussed a scenario in which Oracle Automatic Indexing refused to create a VALID index, because the resultant index was too inefficient to access the necessary rows due to the poor clustering of data within the table. If the performance of such an SQL were critical for business requirements, there […]

Oracle 19c Automatic Indexing: Poor Data Clustering With Autonomous Databases Part I (Don’t Look Down)

I’ve discussed many times the importance of data clustering in relation to the efficiency of indexes. With respect to the efficiency of Automatic Indexes including their usage within Oracle’s Autonomous Database environments, data clustering is just as important. The following demo was run on an Oracle 19c database within the Oracle Autonomous Database Transaction Processing […]

Announcement: “Oracle Performance Diagnostics and Tuning” Webinar – 9-12 July 2019 !!

I’m very excited to announce the first public running of my new “Oracle Performance Diagnostics and Tuning” Webinar will run between 9-12 July 2019 (6pm-10pm AEST): Webinar Series 9-12 July 2019 (start 6pm AEST, end 10pm AEST):  This is a must attend seminar aimed at Oracle professionals (both DBAs and Developers) who are interested in Performance Tuning.  […]

Question: Anything Wrong With Query Performance? (Straight To You)

I have a query that runs pretty darn efficiently, here’s the setup: So the query basically returns 1000 rows based on the CODE column and it does so using an index on CODE. The CBO has got the costings for this just about spot on. For 1000 rows returned, it does so with just 1006 […]

Why INSERT causes TX – row lock contention or TM – contention in #Oracle

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