Working with MySQL database engines

This article is an introduction to working with database engines in MySQL.

About MySQL database engines

Database engines provide the underlying functionality for MySQL to work with and process data.

MyISAM and InnoDB are the two most frequent and popular MySQL database engines. MyISAM is the default engine for MySQL versions prior to 5.5.5, and it works effectively in most situations. However, depending on your requirements, another database engine, such as InnoDB, may be a better solution. InnoDB, for example, supports transactions, whereas MyISAM does not. Foreign keys are also supported by InnoDB, but not by MyISAM.

If you have root access to your server, you have complete control over how and when MySQL uses the various database engines. You can alter the default database engine, the database engine of a specific table, and more.

Determining the default database engine

To determine the default database engine for your installation, type the following command at the mysql> prompt:

SHOW ENGINES;

A list of supported engines appears, along with a brief description and the supported features for each engine. The default database engine is marked DEFAULT in the Support column.

Changing the default database engine

You can change the default database engine for your MySQL installation. After you do this, all new tables that you create will use the new database engine (unless you explicitly set the engine during table creation).

To change the default database engine, follow these steps:

1. Use your preferred text editor to open the my.cnf file on your server. The location of the my.cnf file depends on your Linux distribution:
   • On CentOS and Fedora, the my.cnf file is located in the /etc directory.
   • On Debian and Ubuntu, the my.cnf file is located in the /etc/mysql directory.
2. In the my.cnf file, locate the [mysqld] section.

3. Add or modify the following line in the [mysqld] section. Replace ENGINE with the name of the engine that you want to use as the default:

   default-storage-engine=ENGINE

4. Save the changes to the my.cnf file, and then exit the text editor.

5. Restart the MySQL server using the appropriate command for your Linux distribution:

   • For CentOS and Fedora, type:

     service mysqld restart

   • For Debian and Ubuntu, type:

     service mysql restart

6. To confirm the new default database engine, use the SHOW ENGINES SQL statement.

Determining a table's current database engine

To determine which engine a database table is currently using, type the following command at the mysql> prompt. Replace database with the name of the database that you want to check:

SELECT TABLE_NAME, ENGINE FROM information_schema.TABLES where TABLE_SCHEMA = 'database';

This command displays a list of every table in the database, along with the engine each table is using.

Changing a table's database engine

You can change the database engine for a table that already exists. For example, the following SQL statement shows how to modify a table named myTable to use the InnoDB engine:

ALTER TABLE myTable ENGINE = InnoDB;

Creating a new table with a specific database engine

When you create a table in a database, you can explicitly set its database engine (otherwise, MySQL uses the default database engine during table creation). For example, the following SQL statement shows how to create a table named myTable that uses the MyISAM database engine:

CREATE TABLE myTable (
       id INT NOT NULL AUTO_INCREMENT,
       PRIMARY KEY (id),
       data VARCHAR(20) NOT NULL
) ENGINE MyISAM;

Simiarly, to create a table that uses the InnoDB database engine, you could use the following SQL statement:

CREATE TABLE myTable (
       id INT NOT NULL AUTO_INCREMENT,
       PRIMARY KEY (id),
       data VARCHAR(20) NOT NULL
) ENGINE InnoDB;