参考 DM同步时报错TCPReader get relay event with error: ERROR 1236 (HY000): Could not find first log file name in binary log index file ， 可以尝试开启 dm relay log
v2.0.2 及之后的版本中，通过 start-relay 启动 relay log
https://docs.pingcap.com/zh/tidb-data-migration/stable/relay-log