The following databases exist for MySQL's use. You may read (
SELECT) them, but you must not write (
DELETE) the tables in them. (There are a few exceptions.)
mysql-- repository for
GRANTinfo and some other things.
information_schema-- The tables here are 'virtual' in the sense that they are actually manifested by in-memory structures. Their contents include the schema for all tables.
performance_schema-- ?? [please accept, then edit]