The InnoDB data dictionary is comprised of internal system tables that contain metadata used to keep track of objects such as tables, indexes, and table columns. The metadata is physically located in the InnoDB system tablespace. For historical reasons, data dictionary metadata overlaps to some degree with information stored in InnoDB table metadata files (.frm files).
InnoDB数据字典由内部系统表组成，这些表包含用于跟踪对象的元数据,例如表，索引，列。元数据是存放在innodb系统表空间的物理位置上的，由于历史的原因，数据字典元数据一定程度上与存储在InnoDB表的元数据文件的信息有重叠
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