Maintenance in Managed Service for MySQL®

Maintenance in Managed Service for MySQL® includes:

• Automatic installation of DBMS updates and patches for hosts (including for stopped clusters).
• Other maintenance activities.

Changing a DBMS version is not part of maintenance. For more information about migrating between versions, see MySQL® version upgrade.

Maintenance windowMaintenance window

You can set the maintenance window when creating a cluster or updating its settings:

• The At any time option (default) allows performing maintenance at any time.
• The By schedule option allows you to select the day of the week and UTC time interval for the maintenance. For example, you can choose a time when the cluster is least loaded.

Both active and stopped clusters are subject to maintenance. Maintenance operations may include DBMS updates, applying patches, etc.

In the management console, you select the maintenance start time as an hour interval. In other interfaces, you specify this interval by its sequence number, from 1 to 24.

For example, to start maintenance in the interval from 00:00 to 01:00, put 1; from 04:00 to 05:00, 5.

Maintenance workflowMaintenance workflow

In Managed Service for MySQL® single-host clusters, a master host undergoes maintenance. Therefore, it may become unavailable in case it is restarted.

In multi-host clusters, the maintenance is run as follows:

1. Replicas undergo maintenance one by one. The replicas are queued randomly. If a replica needs to be restarted during maintenance, it will become unavailable.

2. Master host undergoes maintenance and gets updated. If the master host needs to restart and becomes unavailable, one of the replicas will assume its role. Once the upgrade is complete, the host with the highest failover priority will become the new master. In a cluster with several hosts of maximum priority, the one with the least lag behind the master will be selected.

   For the master host to preserve its master role after an upgrade, set the highest failover priority for it. You can set failover priority when creating a cluster or updating host settings.

   If you access a cluster using the FQDN of the master host, the cluster may become unavailable. To make your application continuously available, access the cluster using a special FQDN that always points to the current master host.

How maintenance impacts a clusterHow maintenance impacts a cluster

Depending on its type, maintenance can impact your cluster as follows:

• Show little to no impact on database users.
• Break database connections in place, forcing clients to re-establish their connections.
• Make your cluster read-only for a while.
• Restart the master and trigger master failover to one of the replicas.
• Cause master host failover in the cluster, making the database read-only for a while.

Maintenance tasks have an estimated duration and completion date. These time frames are calculated based on historical data from similar operations. The actual completion times may vary depending on your cluster.