Backing Up Cluster Data¶
You can perform backups with Galera Cluster at the same regularity as with a standard database server, using a backup script. Since replication ensures that all nodes have the exact same data, running a backup script on one node will backup the data on all nodes in the cluster.
The problem with such a simple backup method, though, is that it lacks a Global Transaction ID (GTID). You can use backups of this kind to recover data, but they are insufficient for use in recovering nodes to a well-defined state. Furthermore, some backup procedures can block cluster operations during the backup.
Getting backups with the associated Global Transaction ID requires a different approach.
State Snapshot Transfer as Backup
Taking a full data backup is very similar to node provisioning through a State Snapshot Transfer. In both cases, the node creates a full copy of the database contents, using the same mechanism to associate a Global Transaction ID with the database state. Invoking backups through the state snapshot transfer mechanism has the following benefits:
- The node initiates the backup at a well-defined point.
- The node associates a Global Transaction ID with the backup.
- The node desyncs from the cluster to avoid throttling performance while making the backup, even if the backup process blocks the node.
- The cluster knows that the node is performing a backup and won’t choose the node as a donor for another node.
In order to use this method for backups, you will need to use a script that implements both your preferred backup procedure and the Galera Arbitrator daemon, triggering it in a manner similar to a state snapshot transfer. You would execute such a script from the command-line, as described below:
On the node where you want to have a backup, start the original SST script manually in “joiner” mode. This command opens a socket listening for a connection from “donor”:
$ wsrep_sst_rsync --role 'joiner' --address '10.21.32.1:3333' --datadir '/tmp/backup/' \
--defaults-file '' --defaults-group-suffix '' --parent $$
Note the output:
$ ready 10.21.32.1:3333/rsync_sst
Next, on any node, give the command:
$ garbd --address gcomm://10.21.32.1:4567?gmcast.listen_addr=tcp://0.0.0.0:4560 \
--group my_cluster --sst rsync:10.21.32.1:3333/rsync_sst
Note
In the command, ?gmcast.listen_addr=tcp://0.0.0.0:4560 is an arbitrary listen socket address that Galera Arbitrator opens to communicate with the cluster. You only need to specify this in the event that the default socket address (that is, 0.0.0.0:4567) is busy.
Note
In the command, the value of the --sst option is <sst_method>:<sst_address>, where <sst_address> is given in the output of the joiner script above.
Note
You may find it useful to create your backup script using a modified version of the standard state snapshot transfer script. For information on scripts of this kind, see Scriptable State Snapshot Transfers.
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