This is an old story. It started in 2015 when I found a problem with TOP-N query performance. I wrote a blog post about it and later an update. Here I want to show the full testcase and some updates after a twitter discussion.
This is not a technical post and it’s not related to the database world. It’s just a short experience I had with external HDDs as a simple user so I wanted to share it.
I have an Transcend external HDD for quit a while now. It’s a 2TB disk and it was very useful with my old laptop (where I only had 160GB SSD drive). Since I got my new laptop with 1TB SSD, I hardly use the external disk anymore, but I do keep backups on it (like a good IT guy). This disk contains a second copy of all of my pictures, some documents and other junk (called me old-fashioned, but I don’t want to backup all of this to the cloud).
In the previous post I talked about the order of predicate execution based on the predicate position and inline view.
As promised, in this post I’ll add statistics and see what happens.
In my previous post, I wrote about the parsing operation and what happens first. In the footnote I said that the order doesn’t affect performance, the cost based optimizer doesn’t care about the order of stuff in the query, right? Well, not quite.
When Oracle are adding a new feature to the database, they usually add a parameter to control it. Sometimes, after adding feature and the parameter, they realize that the parameter they chose for controlling the feature is not suitable. It might be confusing, or too general or something else. In these cases they change the parameter in the following version.
After talking a bit about the AWR report (if you haven’t read the previous posts, you can find part 1 here and part 2 here), I think one of the best ways to understand it is to talk about real examples. In this part I’ll give you a few examples and tips regarding the report.