Galera Cluster

What is it about?

In modern database management solutions, uninterrupted operation and high availability are as indispensable as flexibility in scaling options. Only then can the demands of current systems be met, where access fluctuates strongly and there are unpredictable load spikes. The complexity of this maneuver lies in meeting these requirements with minimal infrastructure costs in the cloud.

Galera Cluster helps you with this challenging task: its multimaster clustering solution for databases is based on high-performance synchronous replication, ensuring that all nodes in a database network always have the same data in real time. Available for MariaDB, among others, Galera Cluster minimizes data loss and guarantees the highest reliability. Below, we explain how MariaDB clusters based on Galera Cluster work, the advantages of this technology, and what it is specifically used for.

Using clusters adds high availability to your database by distributing changes across different servers. If one instance fails, others are quickly available to continue providing the service.

 

What exactly are Galeras?

Galera Cluster is a software package for Linux operating systems that enables the creation and management of MySQL, XtraDB, and MariaDB clusters. This clustering application is based on the InnoDB storage engine or its derivative, XtraDB. It is experimentally compatible with the MyISAM engine, which was long used in MySQL and MariaDB as a predecessor to InnoDB. Galera Cluster applies the principle of synchronous replication to data storage across the various independent nodes in the cluster. All processes for copying and modifying stored data occur simultaneously across all primary and secondary storage units, ensuring that the data present in all nodes is always updated and does not differ from one another.

The minimum expression of a Galera Cluster consists of three nodes (the developers generally recommend using an odd number). If one of the nodes fails during data transactions, for example, due to network or system issues, the other two nodes still form the necessary majority to execute the transaction correctly.

 

How does it work?

Clusters come with two general configurations: active-passive and active-active. In active-passive clusters, everything written is kept on a single active server and then copied to one or more passive servers, which are prepared to take over only in the event of a failure of the active server. Some active-passive clusters also allow SELECT operations on passive nodes. In an active cluster, all nodes are read-write, and any changes made to one of them are replicated to the others.

MySQL is an open-source relational database management system that is a popular choice for SQL databases. Galera is a database clustering solution that allows you to set up multimaster clusters through synchronous replication. Galera automatically manages data synchronization across different nodes and allows you to send read and write queries to any node in the cluster.

 

What is its procedure?

Galera Cluster is characterized by the fact that all nodes in the network have the same data at all times. Therefore, the traditional distinction between master database servers (servers where you can write) and slave servers (servers from which you can only read) disappears in clustering software. Users can write data to any storage node, and it will automatically be forwarded to all other participants in the cluster. This feature is also referred to as multimaster.

To ensure this flexible data exchange, Galera Cluster employs a synchronous replication procedure for management, based on certificate exchange. When data is replicated, meaning it is written to one of the Galera MariaDB cluster databases, the following two principles apply:

Each transaction in the database is assigned a unique sequence number. Before a node in the cluster approves the respective changes in the database, it compares the sequence number with the number of the last confirmed transaction. In this check, all nodes reach the same conclusion (Transaction confirmed or Transaction rejected). The node that initiated the transaction communicates the result to the client.

All database replicas are updated in each transaction. Thus, if a transaction is confirmed after certification, all nodes make the corresponding changes in their data records. If the nodes in a Galera Cluster experience any technical issues, they can only be temporarily excluded from synchronous replication.

 

How is a Galera Cluster structured?

The internal architecture of a Galera Cluster is structured around these four components:

• Database Management System (DBMS): The DBMS is the central unit of the cluster. Each node runs the corresponding database server. As mentioned earlier, Galera Cluster is compatible with MySQL and Percona XtraDB, as well as MariaDB.
• wsrep API: The wsrep API defines and implements the interface and access functions for the involved database servers. Additionally, wsrep controls data replication. Among other things, the API provides wsrep hooks (links to the database server for replication) and the dlopen() function, which allows communication with the hooks.
• Galera Replication Plugin: This plugin implements the wsrep API. For this, it provides a layer for the certification process, a layer for replication (including the protocol), and the group communication framework.
• Group Communication Plugins: Galera Cluster provides several extensions for implementing group communication systems like the Spread Toolkit or gcomm. These plugins are based on the group communication framework.

Why is it beneficial?

Switching to this clustering technology offers you flexibility in data storage without sacrificing maximum reliability and availability, which is not possible in standard MariaDB configurations.

Synchronous replication ensures that all storage units involved are updated at all times. Galera Cluster automatically sends all changes to all database units, completely eliminating the need for manual backups or cumbersome backup processes. The multimaster approach also allows access to all servers in the integrated MariaDB database to write, modify, or delete their data. Since nodes can be located near clients, latency can be minimized.

Another advantage of a cluster based on Galera Cluster is the excellent cloud support for such architectures. They are particularly well-suited for flexible cloud-based scalability of database resources. Even distributing data across different data centers is no longer a problem, as each transaction in Galera Cluster only needs to be sent once to each data center.