This document explains Global Transaction Identifiers (GTIDs) in MySQL 5.6, MariaDB 10, and Galera 3. It describes how GTIDs uniquely identify transactions or state changes in each system. In MySQL 5.6 and MariaDB 10, a GTID contains a transaction ID and server ID. In Galera, it contains a sequence number and cluster ID. GTIDs allow for easy replication and failover by ensuring each change is only applied once.