Why Does PDO::__construct() Fail with 'Server Sent Unknown Charset' in Symfony 3 and How Can I Fix It?

Understanding the PDO::__construct() Error: Server Sent Unknown Charset

The PDO::__construct() error encountered while attempting to connect to a MySQL database from Symfony 3 arises when the server transmits a character set (255) that the client does not recognize. This issue occurs due to an update in MySQL 8.0.1, which adopts utf8mb4 as its default character set.

Despite MySQL and PHP operating within Docker containers, the client remains unaware of the new character set. As a result, it interprets the server's response as an unknown value and triggers this error.

Solution: Upgrading the Client

The fundamental solution involves upgrading the client. By incorporating support for utf8mb4, the client can effectively communicate with the server and resolve the issue. This upgrade ensures compatibility with the altered character set.

Temporary Workaround: Modifying the Server's Character Set

Alternatively, a temporary workaround exists to maintain compatibility with non-upgraded clients. By changing the server's character set to utf8, it aligns with the limitations of older clients. This adjustment can be implemented by modifying the /etc/my.cnf file and restarting mysqld with the following settings:

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8


[mysqld]
collation-server = utf8_unicode_ci
character-set-server = utf8

While this workaround resolves the immediate issue, upgrading the client remains the preferred and long-term solution for ensuring optimal compatibility and performance.

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