MySQL

MySQL is an open-source relational database management system that stores data in tables and is queried with SQL. It is owned by Oracle and has been a staple of web hosting for decades.

Why it matters

MySQL is the default database for WordPress and many PHP applications, and it is available on nearly every shared and managed host. Its default InnoDB storage engine provides ACID transactions and row-level locking. When MySQL stops responding or hits its connection limit, sites often show errors such as "Error establishing a database connection".

Example

mysql -h 127.0.0.1 -P 3306 -u appuser -p appdb

SHOW PROCESSLIST;
SHOW VARIABLES LIKE 'max_connections';

The default port is 3306, which you can test with a port checker.

Common mistakes

• Exposing port 3306 to the public internet instead of restricting it to the application server.
• Running with default max_connections while the application opens too many connections.
• Using the old utf8 charset, which is limited to 3 bytes, instead of utf8mb4.

Related

• MariaDB
• Connection pool
• Relational database
• Tool: Port checker

This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.