MySQL 8.4 and newer have extended the Global Transaction ID (GTID) functionality with a new “tag” option. Refresher on GTID A GTID is a unique ID that is assigned to a transaction. This is used if gtid_mode is set to ON . The benefit of this is that a transaction can be uniquely identified in a MySQL replication setup with multiple levels. Among others this makes it easier to refactor a replication tree as a MySQL replica knows which transactions it has seen and can use this to find the right position to start replicating from a new source. The format of GTIDs is documented here . Before GTID was used replication worked based on a file and offset (e.g. file= binlog.000001 ,offset= 4 ), which is unique to every server. A GTID without tag looks like this: 896e7882-18fe-11ef-ab88-22222d34d411:1 This is in the format of <server_uuid>:<txid> . The UUID of the server is in the server_uuid global variable and the txid is the transaction id, which is an increasing number....