Unable to start MySQL or MySQL upgrade fails on Windows: unknown variable

Symptoms

• Unable to start MySQL service or MySQL upgrade fails in Plesk for Windows.

• One of the following errors can be found in
%plesk_dir%MySQLDataservername.err, C:ParallelsInstallerautoinstaller3.log or in the Event Viewer:

  [ERROR] C:Program FilesMySQLMySQL Server 5.6binmysqld.exe: unknown variable 'table_cache=256'
   [ERROR] Aborting

  [ERROR] unknown variable 'key_buffer=256M'
   [ERROR] Aborting

Cause

A declared variable is unknown in MySQL configuration.

Resolution

Disable the unknown variable in MySQL configuration file:

1. Connect to the server via RDP

2. Edit MySQL configuration file located in %plesk_dir%DatabasesMySQLmy.ini with a text editor.

3. Use ‘;‘ character to comment the following line. For example:

   table_cache=256

   It should look like:

   ;table_cache=256

4. Open Services MMC console Run > services.msc

5. Start the service MySQL Server > Right-click > Start

6. In case of the upgrade interruption, continue upgrading MySQL via Plesk GUI or with the following command:

   C:> plesk installer –console

Additional Information:

For Linux – Unable to start MySQL: unknown variable table_cache