7.2. Checking database cluster integrity

When you investigate problems with the MariaDB Galera Cluster, you can check the integrity of the whole cluster by checking specific wsrep database variables on each Controller node.

Procedure

Run the following command and replace VARIABLE with the wsrep database variable that you want to check: 

$ sudo docker exec galera-bundle-docker-0 sudo mysql -B --password="[MYSQL-HIERA-PASSWORD]" -e "SHOW GLOBAL STATUS LIKE 'VARIABLE';"

The following example shows how to view the cluster state UUID of the node: 

$ sudo docker exec galera-bundle-docker-0 sudo mysql -B --password="[MYSQL-HIERA-PASSWORD]" -e "SHOW GLOBAL STATUS LIKE 'wsrep_cluster_state_uuid';"

    +--------------------------+--------------------------------------+
    | Variable_name            | Value                                |
    +--------------------------+--------------------------------------+
    | wsrep_cluster_state_uuid | e2c9a15e-5485-11e0-0800-6bbb637e7211 |
    +--------------------------+--------------------------------------+

The following table lists the wsrep database variables that you can use to check cluster integrity.

表7.1 Database variables to check for cluster integrity

VariableSummaryDescription

wsrep_cluster_state_uuid

Cluster state UUID

ID of the cluster to which the node belongs. All nodes must have an identical cluster ID. A node with a different ID is not connected to the cluster.

wsrep_cluster_size

Number of nodes in the cluster

You can check this on any node. If the value is less than the actual number of nodes, then some nodes either failed or lost connectivity.

wsrep_cluster_conf_id

Total number of cluster changes

Determines whether the cluster was split to several components, also known as partitions. Partitioning is usually caused by a network failure. All nodes must have an identical value.

In case some nodes report a different wsrep_cluster_conf_id, check the wsrep_cluster_status value to see if the nodes can still write to the cluster (Primary).

wsrep_cluster_status

Primary component status

Determines whether the node can write to the cluster. If the node can write to the cluster, the wsrep_cluster_status value is Primary. Any other value indicates that the node is part of a non-operational partition.