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 …
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