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# Galera

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Galera is a synchronous multi-master cluster for MySQL/InnoDB databases.

Note Currently replication is supported only for InnoDB tables.

## Installation

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 galera package. Also you will need rsync and lsof packages for rsync method.

Start/Enable the `mysqld.service` daemon.

## Configuration

You need to configure the cluster.

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

    /etc/my.cnf.d/server.cnf

    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 does not need to be unique) for each node, e.g.:

    /etc/my.cnf.d/server.cnf

    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:

    /etc/my.cnf.d/server.cnf

    wsrep_cluster_name='my_galera_cluster'

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

    /etc/my.cnf.d/server.cnf

    wsrep_sst_method=rsync

Make sure you also set the following options:

    /etc/my.cnf.d/server.cnf

    wsrep_on=ON
    wsrep_provider=/usr/lib/galera/libgalera_smm.so
    default_storage_engine=InnoDB
    innodb_autoinc_lock_mode=2
    binlog_format=row

When you have finished with `/etc/my.cnf.d/server.cnf`, bootstrap the mysqld service on the first node (ONLY on the first node):

    # galera_new_cluster

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, this will show you wsrep-related status variables:

    mysql> SHOW STATUS LIKE 'wsrep_%';

    | 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 the 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 `mysqld.service`.

## See also

- MariaDB Wiki
- Percona XtraDB Cluster's documentation
- How to Bootstrap MySQL or MariaDB Galera Cluster
- How To Recover MariaDB Galera Cluster After Partial or Full Crash[dead link 2024-10-12—HTTP 404]

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- Database management systems

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