Recent Posts by Nigel Bayliss

You were hoping for an uneventful day at work when you notice that you have a critical workload query that is taking much longer to execute than usual, and you can see that it is beginning to affect your service levels. You suspect that it has a sub-optimal execution plan and you need to get it sorted out immediately. Is there a quick and easy way to do that? Automatic SQL plan management can deal with this type of issue without DBA intervention, but what can you do if this...

It's nearly time for Oracle OpenWorld 2019. As ever, there are a number of interesting optimizer-related sessions in the catalogue (and I see there's one on MySQL too).  Here's ours: If you're coming to OOW but can't make the session, then come and speak to the Oracle developers themselves at the demo booths in Moscone South. We're in booth "ODB-013". I'll be around there as much as possible too. What makes OOW special for me is being able to listen to your feedback first-hand;...

Occasionally I want to get historical information on histogram changes for a particular table. I have had a script in my back pocket for a long while so I thought I'd share it in the Oracle Optimizer GitHub repository. My main motivation for doing this is that I still consider the script experimental and I would like feedback from the field. Feel free to comment below, particularly if you see room for improvement or flaws. Perhaps the output could be clearer or maybe there...

Introduction I am often asked, “How does Oracle choose which columns need a histogram?” Also, “Why have I got a histogram on my primary key column?” Jonathan Lewis posted an explanation in response to the latter question some while ago, but I thought I’d cover a little bit more on this topic and focus on how Oracle chooses which columns should have histograms. In particular, I want to clarify how the database determines what histograms to create if you use the...

Oracle Database 19c adds a new feature called automatic SQL plan management. This post covers: What is automatic SQL plan management and how it works. Why it is important for you to be aware of it. How to configure. Summary. Where is it available? Recently we changed the availability of this feature so that the new auto mode is no longer available on all platforms in Oracle Database 19c. In addition, it is no longer the default setting.See Automatic SQL Plan Management in table 1-6...

For those of you that want to keep up-to-speed with the latest changes, this post includes a quick summary of the headline new features in Oracle Database 19c with links to the documentation. In addition, most of the new optimizer white papers have been published. You will find links to them in the new Oracle Query Optimization page (and there will be further updates to this page soon). Automatic Indexing This is a complex and sophisticated piece of functionality...

A popular enhancement request I see is to provide an easier way to diagnose issues with SQL plan baselines; in particular the situation where a SQL plan baseline is ACCEPTED but is not being used for whatever reason. This is rare, but can happen if changes are made to the database such as dropping indexes or changing partitioning schemes. If a SQL plan baseline can't be used, you will see something like this in Oracle Database 19c: So why did it fail? In this example I captured...

Since LiveSQL is running on Oracle Database 19c, now is the time to be one of the first to take a look at the new Hint Usage Reporting feature. Trying to figure out why a hint is not being used is not on my top-100-fun-things-to-do list. Luckily, there's now a way to do it much more easily than before. Here is a very simple example - but it's just the tip of the iceberg... create table mytab (a number(10) primary key); insert into mytab values (1); commit; exec...

Oracle Database 18c Standard Edition includes a new way to control SQL execution plans. Stored outlines were deprecated in Oracle Database 11g Release 1 and SQL plan management (SPM) was only available in Oracle Database Enterprise Edition. This meant that many DBAs continued to use stored outlines in Standard Edition and they continue to work to this day. At some point in the future we will begin to remove support for stored outlines so, to avoid leaving a hole in SE, we...