In this blog, we’ll discuss things to watch out for during a MySQL downgrade.

Previously, I wrote the blog MySQL upgrade best practices. Besides upgrading your MySQL version, sometimes you need to downgrade. When it comes to downgrading MySQL, there are two types of downgrade methods supported:

1. In-Place Downgrade: In this method, you use the existing data directory and replace MySQL binaries, followed by a

   mysql_upgrade

    execution. This type of downgrade is supported within the same release series. For example, in-place downgrades are supported when moving from 5.7.12 to 5.7.10.
2. SQL Dump Downgrade: An SQL dump is …

Percona announces the release of Percona Server 5.6.33-79.0 on October 18th, 2016. Download the latest version from the Percona web site or the Percona Software Repositories.

Based on MySQL 5.6.33, including all the bug fixes in it, Percona Server 5.6.33-79.0 is the current GA release in the Percona Server 5.6 series. Percona Server is open-source and free – this is the …

Here is the second in a series of posts about CTEs, a new feature of MySQL 8.0, available in this Labs release. The first post ended with:

Inside the recursive CTE definition (the part in AS (…)), some syntax constraints must be respected […]

• a recursive SELECT mustn’t contain GROUP BY, aggregate functions
  (like SUM), ORDER BY, LIMIT, DISTINCT (this rule doesn’t apply to the non-recursive/anchor/seed SELECT)
• a recursive SELECT must reference the CTE only once and only in its
  FROM clause, not in any subquery.

…

The Theory

Generated Columns is a feature released on MySQL 5.7. They can be used during CREATE TABLE or ALTER TABLE statements. It is a way of storing data without actually sending it through the INSERT or UPDATE clauses in SQL. The database resolves what the data will be.

There are two types of Generated Columns: Virtual and Stored. They work with:

• mathematical expressions (product_price * quantity)
• built-in functions (RIGHT(), CONCAT(), FROM_UNIXTIME(), JSON_EXTRACT())
• literals (“2”, “new”, 0)

Besides that, they can be indexed but they don’t allow …

In this blog post, we’ll explain how to update the signing key for Percona Debian and Ubuntu packages.

Some of the users might have already noticed following warning on Ubuntu 16.04 (Xenial Xerus):

W: http://repo.percona.com/apt/dists/xenial/InRelease: Signature by key 430BDF5C56E7C94E848EE60C1C4CBDCDCD2EFD2A uses weak digest algorithm (SHA1)

when running apt-get update.

Percona .deb packages are signed with a key that uses an algorithm now considered weak. Starting with the next release, Debian and Ubuntu packages are signed with a new key that uses the much stronger SHA-512 algorithm. All future package release will also contain the new algorithm.

You’ll need to do one of the …

This blog updates Stephane Combaudon’s blog on MySQL performance tuning, and covers MySQL 5.7 performance tuning immediately after installation.

A few years ago, Stephane Combaudon wrote a blog post on Ten MySQL performance tuning settings after installation that covers the (now) older versions of MySQL: 5.1, 5.5 and 5.6. In this post, I will look into what to tune in MySQL 5.7 (with a focus on InnoDB).

The good news is that MySQL 5.7 has significantly better default values. Morgan Tocker created a page with a complete list of features in MySQL 5.7, and is a great reference point. For example, the …

Encrypt your credentials using GPG

This blog post will look how to use encryption to secure your database credentials.

In the recent blog post Use MySQL Shell Securely from Bash, there are some good examples of how you might avoid using a ~/.my.cnf – but you still need to put that password down on disk in the script. MySQL 5.6.6 and later introduced the  –login-path option, which is a handy way to store per-connection entries and keep the credentials in an encrypted format. This is a great improvement, but as shown in Get MySQL Passwords in Plain Text from .mylogin.cnf, …

Starting with the 8.0 optimizer labs release the MySQL server now supports descending indexes. As I will detail in this post, this new feature can be used to eliminate the need for sorting results, and lead to performance improvements in a number of queries.…

In this blog post, I’ll look at how to use the loose_ option prefix in my.cnf in MySQL.

mysqld throws errors at startup – and refuses to start up – if a non-existent options are defined in the my.cnf file.

For example:

2016-10-05 15:56:07 23864 [ERROR] /usr/sbin/mysqld: unknown variable 'bogus_option=1'

The MySQL manual has a solution: use the loose_ prefix option in my.cnf file.

In the prior example, if we specify loose_bogus_option=1 in the my.cnf file, instead of bogus_option=1, mysqld starts successfully and ignores that option.

This is useful in three situations:

1. Using …

This blog discusses the gradual end of MyISAM in MySQL.

The story that started 20 years ago is coming to its end. I’m talking about the old MyISAM storage engine that was the only storage provided by MySQL in 1995, and was available in MySQL for 20+ years. Actually, part of my job as a MySQL consultant for 10+ years was to discover MyISAM tables and advise customers how to convert those to InnoDB.

(Check your MySQL installation, you may still have MyISAM tables).

MySQL 5.7 still used MyISAM storage for the system tables in the MySQL schema.

In MySQL 8.0 (DMR version as of writing), the MyISAM storage engine is still available. But in a very limited scope:

• After …