Doesn't adding an index only take out a brief metadata lock at the start of the operation, and then leave the table safe for queries while the rest of indexing

Doesn't adding an index only take out a brief metadata lock at the start of the operation, and then leave the table safe for queries while the rest of indexing completes? https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-operations.html https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-op...