Perth, Western Australia - 6th to 10th January 2014

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Synchronous Replication Even Across Datacentres

Project: MariaDB,MySQL,Galera

MariaDB from 5.5 includes Galera Clustering, based on the wsrep library developed by the Finnish company Codership.

Traditionally, synchronous replication requires a two-phase commit process. This works reasonably well within a single datacentre, although performance can still degrade with a larger number of systems in the cluster.

Eventual consistency is another approach, typically utilised in (non-RDBMS) distributed database systems such as Google's BigTable. While valid in many situations, it's unsuitable for some applications and a hassle in others.

Galera uses a different mechanism again, which can crudely be described as "virtual synchrony": generally speaking, all members of the cluster will be updated at the same time as the system initiating the write. This makes application writers very happy. Because fewer communication cycles are required, it can also work across datacentres and even over intercontinental links. This means we can do active-active across multiple datacentres, and that's not just shiny but something many people really want/need.

This talk provides an overview of these different approaches to clustered replication and then delves into the technical detail of how Galera does its magic.

Arjen Lentz

After working for, Arjen started Open Query ( in 2007. Since then this primary business has spawned various other initiatives including Blue Hackers ( and Upstarta (

Arjen lives in Brisbane with his wife Claire and blended family of 4 kids + cat Figaro.