参考rul:https://www.cnblogs.com/zengkefu/p/5674945.html
Summarized as follows:
1. Except for the modification of the primary key, the change of the field type and length, and the change of the character set, all others support ddl. Some operations take up a lot of resources.
2. Make sure that no major transactions occur before modification.
3. Record the ddl process dml through row_log.
4. The ddl process is killed and has no effect. Abnormal power failure, due to the influence of the temporary table, requires special manual repair.