Manual creation of database directories under the data directory (for example, with mkdir) is unsupported. 不支持在数据目录下手动创建数据库目录（例如，使用mkdir）。Manually created database directories are not recognized by the MySQL Server.MySQL服务器无法识别手动创建的数据库目录。

DDL operations take longer due to writing to storage, undo logs, and redo logs instead of .frm files.由于写入存储、撤消日志和重做日志而不是.frm文件，DDL操作需要更长的时间。