SQL Galera Cluster is a high availability and scalability solution for MySQL or MariaDB databases. It uses the Galera replication plugin to provide synchronous multi-master replication, ensuring that all nodes in the cluster have the same data at all times.
When a new node joins the cluster, it needs to synchronize its data with the existing nodes. This process is called State Snapshot Transfer (SST) and there are multiple methods available to perform this transfer.
Understanding SST Methods
There are three common SST methods in SQL Galera Cluster:
- mysqldump
- This method creates a logical representation of the database in the form of SQL statements. It then transfers these SQL statements to the joining node, which applies them to recreate the data. This method is suitable for smaller databases but can be slow for large databases.
- rsync
- Rsync is a file-based synchronization method that copies the data files from one node to another. It is faster compared to mysqldump but requires the data directory to be available on a shared filesystem.
- Percona XtraBackup
- Percona XtraBackup is a hot backup tool that takes a copy of the MySQL data directory while the database is still running. It transfers the backup files to the joining node, which applies them to synchronize the data. This method is the fastest and most efficient for large databases.
Configuring SST Methods
To configure the SST method in SQL Galera Cluster, you need to modify the cluster configuration file (my.cnf). Locate the [sst] section and update the method parameter with the desired SST method:
[sst]
method = mysqldump
Replace mysqldump with rsync or xtrabackup depending on your preference.
Managing SST Methods
Once the SST method is configured, SQL Galera Cluster will automatically use it whenever a node joins the cluster. However, you can also manually trigger an SST if needed.
To manually start an SST, you can use the wsrep_sst_method system variable:
SET GLOBAL wsrep_sst_method = 'rsync';
Replace rsync with the desired SST method.
Conclusion
Configuring and managing SST methods in SQL Galera Cluster is essential for ensuring the smooth operation and synchronization of nodes in the cluster. By understanding the available SST methods and configuring them correctly, you can optimize the performance and scalability of your database cluster.
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