Which of these is the metadata log?

This question asks about a special type of log in MySQL that stores information about changes made to the database's structure. This information is called metadata.
Let's look at the options:
Option A: error log - This log records errors that happen during MySQL's operation. It doesn't store information about database structure changes.
Option B: ddl log - This is the correct answer! The DDL log (Data Definition Language log) specifically tracks changes made to the database's structure, like creating, altering, or dropping tables.
Option C: binary log - This log records all the changes made to the database, including both data modifications and structure changes. It's more comprehensive than the DDL log.
Option D: relay log - This log is used in replication, where changes are copied from one server to another. It's not directly related to storing metadata about the database structure.
So, the answer is Option B: ddl log.