Feed: Planet MySQL
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Author: Frederic Descamps
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Yesterday I decided to upgrade the database server of lefred.be running the latest WordPress to MySQL 8.0.

The previous version was 5.7.19.

My dedicated server is still running on CentOS 6.x, and I had just to enable the MySQL Community 8.0 yum repository and upgrade the rpms:

# yum update mysql-community-server --enablerepo=mysql80-community

After the upgrade, I had to modify my.cnf to remove the lines related to the non regretted Query Cache:

#query_cache_type=0
#query_cache_size=0

After this, I could start mysqld and run mysql_upgrade.

I tried to connect with the command line client and it worked perfectly.

Then, I wanted to remove the maintenance mode on lefred.be but WordPress returned me an error that it couldn’t connect to the database:

I verified the mysql error log, nothing wrong (bad credentials are logged), and no error in the apache’s log.

I decided to run WordPress in debug mode :

in wp-config.php set

define('WP_DEBUG', false)

Then I could see this error message that sounded familiar:

Warning: mysqli_real_connect(): Server sent charset (255) unknown to the client. Please, report to the developers in /var/…/www/wp-includes/wp-db.php on line 1548

I modified again my.cnf to add the following line under [mysqld]:

collation-server = utf8mb4_general_ci

After a restart of mysqld, everything went back normal !

The MySQL connector used on my system for PHP is php55w-mysqlnd-5.5.38-1.w6.x86_64:

Name        : php55w-mysqlnd
Arch        : x86_64
Version     : 5.5.38
Release     : 1.w6
Size        : 956 k
Repo        : installed
From repo   : webtatic
Summary     : A module for PHP applications that use MySQL databases
URL         : http://www.php.net/
License     : PHP
Description : The php-mysqlnd package contains a dynamic shared object that will add
            : MySQL database support to PHP. MySQL is an object-relational database
            : management system. PHP is an HTML-embeddable scripting language. If
            : you need MySQL support for PHP applications, you will need to install
            : this package and the php package.
            : 
            : This package use the MySQL Native Driver

The next post will be related to the workload analysis using performance_schema & sys and see if something can be improved.

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