Description: The ‘gtid_subscribed’ variable is an essential component in MySQL database replication, specifically in the context of GTID (Global Transaction Identifier) based replication. This variable shows the GTIDs to which the server has subscribed, meaning it indicates which transactions have been recognized and accepted by the server in a replication environment. GTID-based replication allows for more efficient and accurate tracking of transactions in a distributed system, facilitating fault recovery and synchronization between servers. By using GTIDs, it can be ensured that each transaction is applied only once, avoiding duplication issues and ensuring data integrity. The ‘gtid_subscribed’ variable is crucial for managing replication, as it allows database administrators to monitor and control which transactions have been replicated and which are still pending, contributing to more effective resource management and greater overall system stability.
History: The introduction of GTID in MySQL dates back to version 5.6, released in 2013. This system was designed to improve replication in distributed database environments, addressing the limitations of previous replication methods that relied on binary log positions. With GTID, each transaction is uniquely identified, simplifying replication management and disaster recovery. Since its implementation, GTID has evolved and become a standard feature in later versions of MySQL, enhancing the reliability and usability of replication.
Uses: The ‘gtid_subscribed’ variable is primarily used in the management of replication in MySQL. It allows database administrators to verify which transactions have been replicated to a specific server and which are still pending. This is especially useful in environments where high availability and data consistency are required, such as in critical applications. Additionally, it facilitates fault recovery, as administrators can quickly identify which transactions need to be replicated again in the event of an error.
Examples: A practical example of using ‘gtid_subscribed’ is in a master-slave replication environment, where the slave server can query this variable to determine which transactions it has received and applied. If the master server experiences a failure, the administrator can use the information from ‘gtid_subscribed’ to ensure that the slave is fully up-to-date before promoting it to master. This ensures that no data is lost and that the transition is smooth.
