A safe MySQL upgrade that wasn't so safe

A MySQL database upgrade using a replica went wrong when an AUTO_INCREMENT primary key added to a table years earlier caused IDs to be assigned in different orders on the source and replica databases. During replication, MySQL's MIXED binary log format automatically switched to ROW mode for the affected table (due to AUTO_INCREMENT safety concerns), copying source IDs that no longer matched the replica's row ordering and breaking foreign key references in one dependent table while five others remained correct. The incident highlights that AUTO_INCREMENT columns in replicated environments require careful consideration, as they can produce inconsistent row ordering between source and replica.