MyISAM

MyISAM is a storage engine used by the MySQL relational database management system. It stores each table as a set of files on disk, typically a data file (.MYD), an index file (.MYI), and a table definition file (.frm). This file-per-table architecture makes backups and certain maintenance tasks straightforward and observable in the filesystem.

A defining characteristic of MyISAM is its locking model. It uses table-level locking, which means read and write operations affect the entire table. This can limit concurrency for write-heavy workloads compared with engines that support row-level locking. MyISAM is non-transactional and does not support foreign key constraints, so applications must enforce data integrity at the application layer.

MyISAM supports features such as full-text indexing in its indexed search capabilities, and it is generally noted for fast read performance on simple workloads. It does not provide the ACID guarantees of transactional engines; there is no automatic crash-safe commit or rollback mechanism, and recovery from corruption often relies on external repair tools.

Maintenance and recovery are aided by the myisamchk utility, which can check, repair, or optimize MyISAM tables. Because MyISAM does not log transactions, it is less suitable for applications requiring strong data consistency under concurrent updates.

History and status: MyISAM was the default MySQL storage engine for many years prior to the rise of InnoDB. Since MySQL 5.5, InnoDB has been the default engine, but MyISAM remains available and is still used for legacy applications or non-transactional workloads. Developers considering MyISAM should weigh its speed and simplicity against its lack of transactional guarantees and row-level locking.