The data dictionary schema stores dictionary data in transactional (InnoDB) tables. Data dictionary tables are located in the mysql database together with non-data dictionary system tables.

Data dictionary tables are created in a single InnoDB tablespace named mysql.ibd, which resides in the MySQL data directory. The mysql.ibd tablespace file must reside in the MySQL data directory and its name cannot be modified or used by another tablespace.

Dictionary data is protected by the same commit, rollback, and crash-recovery capabilities that protect user data that is stored in InnoDB tables.