This MySQL replication error — fatal error 1236 / Replica has more GTIDs than the source has, using the source's SERVER_UUID — shows the importance of thinking before acting. I am glad a non-DBA Colleague asked me about it, because if he had restarted replication, it would have caused a much bigger mess.
Often, we are tempted — or pushed — to just restart things as quickly as possible. In this specific case, restarting replication is unsafe as it leads to a replication breakage in the best case, and to silent data corruption in the worse case. It is a great example of the following two advice : 1) do not make a bigger mess, do not failover, do not reboot, and 2) we cannot just bring the database back up, we have things to do first to make this safe. Let's explore all these.
