Galera

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Galera is a synchronous multi-master cluster for MySQL/InnoDB databases. For more information about the product and its features, please visit the official webpage.

Note: Currenty replication is supported only for InnoDB tables.

Instalation

The two components Galera cluster comprised of are Galera plugin itself and a patched version of MySQL server which connect using wsrep API.

Install the mysql-wsrepAUR and galeraAUR packages from the AUR.

Enable at startup

To enable mysql daemon to start at boot, add the mysqld service to systemd:

# systemctl enable mysqld.service

Configuration

Once you have installed the galeraAUR and mysql-wsrepAUR packages, you need to configure the cluster.

On each node edit /etc/mysql/my.cnf and update the wsrep_cluster_address variable so it contains the list of all nodes in the cluster:

wsrep_cluster_address="gcomm://192.168.1.4,192.168.1.5,192.168.1.6"

Change the variables wsrep_node_address and wsrep_node_name to the IP address/hostname and name(this doesn't need to be unique) for each node, e.g.:

wsrep_node_address='192.168.1.4'
wsrep_node_name='node1'

The wsrep_cluster_name variable should contain the same name for all cluster nodes:

wsrep_cluster_name='my_galera_cluster'

Also, set wsrep_sst_method to the desired state snapshot transfer method, the preferred one is rsync.

wsrep_sst_method=rsync

When you have finished with /etc/mysql/my.cnf, start the mysqld service on the first node:

# systemctl start mysqld-bootstrap.service

This will bootstrap the cluster. Use MySQL's command line tool to log in as root into your MySQL server:

$ mysql -p -u root

Check the status of the cluster:

mysql> SHOW STATUS LIKE 'wsrep_%';

This will show you wsrep-related status variables:

...
| wsrep_local_state          | 4                                    |
| wsrep_local_state_comment  | Synced                               |
| wsrep_cert_index_size      | 0                                    |
| wsrep_causal_reads         | 0                                    |
| wsrep_incoming_addresses   | 192.168.1.4:3306                     |
| wsrep_cluster_conf_id      | 1                                    |
| wsrep_cluster_size         | 1                                    |
| wsrep_cluster_state_uuid   | 6cd96745-2ea8-11e3-bbc8-d666651b51ef |
| wsrep_cluster_status       | Primary                              |
| wsrep_connected            | ON                                   |
| wsrep_local_index          | 0                                    |
| wsrep_provider_name        | Galera                               |
...

If you use xtrabackup or mysqldump SST method, you will need to create a MySQL user for sst transfers.

Once you configured the first node, you should be able to start all other nodes with:

# systemctl start mysqld.service

Troubleshooting

TODO

See also

Galera Wiki Percona XtraDB Cluster’s documentation