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 …

Last week I had to downgrade from MySQL 5.6 to 5.5. The reason for this was that the application used a very old Connector/J and that's incompatible with MySQL 5.6 because the removal of SET OPTION syntax.

We're now planning to upgrade Connector/J to be able to upgrade to 5.6 again.

There are two methods of downgrading:

• Dump/Restore with mysqldump. This is easy and reliable, but can take more time.

• In place (replace binaries, don't change data). This fast, but won't work if file formats have changed.

As expected this is documented in the MySQL Reference Manual.

I went for the in place method. I expected this to work without many issues as this database was not using the fancy new features like fulltext indexes for InnoDB. All tables used …