The unique architecture of MySQL permits multiple storage engines with different capabilities to be accessed via the same SQL language and APIs. Starting with version 5.1, MySQL AB has promoted the idea of a “pluggable” storage engine architecture, which permits multiple storage engines to be added to MySQL. Currently, however, most users have accessed only those storage engines that are distributed by MySQL AB, and are linked into the binary (executable) releases.

Since 2001, MySQL AB has distributed the InnoDB transactional storage engine with its releases (both source and binary). Beginning with MySQL version 5.1, it is possible for users to swap out one version of InnoDB and use another. The pluggable storage engine architecture also permits Innobase Oy to release new versions of InnoDB containing bug fixes and new features independently of the release cycle for MySQL. Users can thus take advantage of these new versions of InnoDB in the context of their deployed MySQL installations.