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How Well a Query Optimizer Handles Subqueries?

At the beginning of December, at the UKOUG Tech17 conference in Birmingham (GB), I presented a comparison of the query optimizers of MySQL 8.0.3 and PostgreSQL 10.1. One of the things I talked about is their ability to handle subqueries. I summarized my findings with the following sentence:

Simple sub-queries that are not correctly optimized were observed.

It goes without saying that such a sentence leaves a lot of questions open. After all, it is just a summary. The aim of this post is to show you which subqueries I tested, and to compare my expectations with the execution plans generated by the query optimizers. In addition, since I’m not limited in time and scope as during a 50-minute presentation, I also discuss how the Oracle Database 12.2 query optimizer handles the same queries.

The Rosetta Stone of Database Platforms

This is a living document that I will continue to update and will add new database platforms to as I go along in my career.  I spend a lot of time translating database platforms I’ve worked in for all tiers of the technical business.  It just seems natural that we might need a location on the web where that information is kept.

Video: Amazon Web Services (AWS) : Relational Database Services (RDS) for MySQL

Here’s another video on my YouTube channel. This one is a quick run through of RDS for MySQL, a DBaaS offering from Amazon Web Services.

The video was based on this article.

If you watch the little outtake at the end you will hear me cracking up with the goofiest while filming Brian ‘Bex’ Huff‘s clip. :)



MySQL 5.7 is now GA

I noticed a retweet by Giuseppe Maxia about MySQL 5.7 being generally available now.

You can get the community download here, but more importantly the main yum repository page has the 5.7 repo as GA. Happy days!

I guess I know what I’m doing when I get home…





Databases Running in the Cloud

cloudI’ve been playing around with running databases in the cloud recently. It’s quite simplistic stuff, just to get a feel for it and investigate the possibilities of using it for some projects at work. Here’s what I’ve got so far.

MySQL : What management tools do you use?

A quick question out to the world. What management tools do you use for MySQL?

We currently have:

MySQL Upgrades

I read Wim Coekaerts post about the MySQL 5.6.20-4 this morning. I logged on to my server and did the following command as root.

# yum update -y

That’ll be the upgrade done then… :)

If you are using MySQL on Linux you can use the MySQL Repository for your distribution, rather than using the bundled MySQL version, to make sure you stay up to date with the latest and greatest. As long as you stay within a point release (5.6, 5.7 etc.) of the latest version, upgrades should really be as simple as a “yum update”.

Oracle Linux and MySQL : Progress

A few months ago I wrote about some MySQL on Oracle Linux migrations we were working through. It’s been a long time coming, but last weekend was the go-live for this batch of migrations. So far so good! :)

Most of the elapsed time since my last post on this subject has been spent with the developers and users testing the migrations.

Oracle Linux and MySQL

I’m in the process of taking on some of the MySQL databases in my company. The first ones are MySQL 4.1 running on Windows, so we are upgrading them to MySQL 5.6 on Oracle Linux. As with many of our systems, these will be running on VMware virtual machines.

Since the current installations are so old, we are planning on dumping out the data and creating fresh installations on the new systems. Based on the advice I got from Ronald Bradford and Sheeri Cabral, we are also taking this opportunity to switch to InnoDB and utf8, rather than MyISAM and latin1 that are currently used.

Quiet Release MySQL Plugin — Bug Fixes

This is just a small bug-fix release of the plugin. It has actually been quietly released for a while now. If you have downloaded the plugin recently, you have the latest version. To be sure, check the version in the Console, or you can see it in the file name.

There are two bugs fixed:
1. Deployment on an OMS hosted on Solaris didn’t work. (And I suspect it could be the same for Agents on Solaris.)
2. Changing thresholds on the metrics caused the error “Modification of Target Monitoring Settings has Failed”. Also, applying monitoring template was failing for the same reason.