Percona XtraDB Cluster is a fully open-source high-availability solution for MySQL. It integrates Percona Server and Percona XtraBackup with the Galera library to enable synchronous multi-master replication.

A cluster consists of nodes, where each node contains the same set of data synchronized accross nodes. The recommended configuration is to have at least 3 nodes, but you can have 2 nodes as well. Each node is a regular MySQL Server instance (for example, Percona Server). You can convert an existing MySQL Server instance to a node and run the cluster using this node as a base. You can also detach any node from the cluster and use it as a regular MySQL Server instance.

Benefits:

• When you execute a query, it is executed locally on the node. All data is available locally, no need for remote access.
• No central management. You can loose any node at any point of time, and the cluster will continue to function without any data loss.
• Good solution for scaling a read workload. You can put read queries to any of the nodes.

Drawbacks:

• Overhead of provisioning new node. When you add a new node, it has to copy the full data set from one of existing nodes. If it is 100GB, it copies 100GB.
• This can’t be used as an effective write scaling solution. There might be some improvements in write throughput when you run write traffic to 2 nodes versus all traffic to 1 node, but you can’t expect a lot. All writes still have to go on all nodes.
• You have several duplicates of the data, for 3 nodes you have 3 duplicates.

Components

Percona XtraDB Cluster is based on Percona Server running with the XtraDB storage engine. It uses the Galera library, which is an implementation of the write set replication (wsrep) API developed by Codership Oy. The default and recommended data transfer method is via Percona XtraBackup.