Explain the purpose of MySQL Group Replication Autorejoin.

MySQL Group Replication Autorejoin is a feature designed to enhance the fault tolerance and availability of MySQL Group Replication setups. To understand its purpose technically, let's break it down:

  1. MySQL Group Replication: This is a MySQL plugin that enables you to create a group of MySQL servers which act as a single, coordinated, and fault-tolerant database cluster. It provides distributed state machine replication with strong coordination guarantees. Each member in the group replicates data and transactions to other members in real-time.
  2. Fault Tolerance and High Availability: In a MySQL Group Replication setup, fault tolerance refers to the system's ability to continue functioning despite the failure of one or more components. High availability means the system is designed to minimize downtime and ensure that services remain accessible even in the presence of failures.
  3. Autorejoin: Autorejoin is a feature that automates the process of rejoining a member back into the group after it has been temporarily removed due to a network partition or failure detection. When a member leaves the group unexpectedly (e.g., due to network issues, server failure, or transient issues), it is desirable to have mechanisms in place to automatically reintegrate it into the group once it becomes available again.
  4. Purpose:
    • Fault Recovery: The primary purpose of MySQL Group Replication Autorejoin is to facilitate fault recovery. By automatically rejoining a failed member back into the group, it helps restore the desired level of replication redundancy and ensures that the group remains operational even in the face of failures.
    • Reduced Manual Intervention: Without autorejoin, administrators would need to manually intervene to bring the failed member back into the group, which could lead to delays in recovery and potential human errors. Autorejoin automates this process, reducing the need for manual intervention and minimizing downtime.
    • Improved Availability: By quickly reintegrating failed members, autorejoin helps maintain high availability of the database cluster. This is crucial for applications and services that require continuous access to the database without significant interruptions.
  5. Mechanism:
    • Autorejoin works by continuously monitoring the status of group members and detecting when a member becomes unavailable or is removed from the group.
    • Upon detecting a failed member, autorejoin initiates the process of rejoining the member back into the group as soon as it becomes reachable again.
    • The rejoining process typically involves synchronizing the data between the failed member and the rest of the group to bring it up-to-date before allowing it to resume active participation in replication.