A total of four MySQL architecture, as the division in the above figure in dashed lines. First, the top of MySQL service is not unique, most give the network a client / server tools or services have a similar architecture. For example: connection handling, authorization and authentication, and security. The second layer architecture includes most of MySQL's core services. Including: query parsing, analysis, optimization, caching, and all built-in functions (for example: date, time, math and encryption function). At the same time, all across storage engine functions are implemented in this layer: stored procedures, triggers, views, and so on. The third layer contains a storage engine. The storage engines in MySQL storage and retrieval of data. Server communicates through the API, and the storage engine. These interfaces shielding differences between storage engine, such that the differences of the upper transparent inquiry procedure. Storage Engine API may contain a dozen underlying function, for performing a "start transaction" and other operations. But generally not storage engine to parse SQL (InnoDB resolves foreign key definition, since it does not itself implement the function), not between different storage engines communicate with each other, but simply in response to the upper layer request to the server. The fourth layer includes the file system, all of the tables and data structures, and ultimately logs user operation in the form of files stored on the hard disk.