Overview

MySQL Group Replication was released as GA with MySQL 5.7.17. It is essentially a plugin that, when enabled, allows users to set replication with this new way.

There has been some confusion about the stability and usability of this release. Until recently, MySQL Group Replication (MGR) was only available in the Labs, which traditionally denotes a preview or an use-at-your-own-risk feature. Several months ago we saw the release of Group Replication as a Docker image, which allowed users to deploy a peer-to-peer cluster (every node is a master.) However, about one month after such release, word came from Oracle discouraging this setup, and inviting users to use Group Replicator in …

Replication is a hot topic in MySQL 5.6, and for good reason: There are many excellent features that make it a strong well-supported feature, from the new Global Transaction Identifiers (GTIDs), to simplified replication configuration and automated failover using MySQL Utilities (now available in alpha as a separate download).

Circular Replication

The simplest topology consists of a master server that accepts changes, and slaves that replicate those changes from the master. A common requirement is for a network to have multiple servers that accept changes and replicate to each other. This is possible by means of circular …

In the first part of this article we examined the types of conflicts and their causes. In this part, we will analyse some of the methods available to deal with conflicts.

Pessimistic locking (or: conflicts won't happen)

Applicability: synchronous clusters with 2pc

We've covered this topic in the previous article, but it's worth repeating. If you use a synchronous cluster, you don't have conflicts. For example, MySQL Cluster ensures consistent data with updates coming from different nodes. However, MySQL Cluster is not a replacement for a MySQL server, and it has severe limitations.

Optimistic locking

Applicability: synchronous clusters without 2pc (Galera)

Conflicting transactions proceed on different nodes with local locking. The last one then …

What is a conflict?

Readers of this blog know that one of my favorite tools, Tungsten Replicator, can easily create multi-master replication topologies, such as all-masters, star, fan-in. While this is good news for system designers and ambitious DBAs, it also brings some inconvenience. When you allow updates to happen in more than one master, you risk having conflicts. You may have heard this term before. For the sake of clarity, let's define what conflicts are, before analyzing each case in detail.

You have a conflict when several sources (masters) update concurrently the same data in asynchronous replication.

It's important to stress that this happens with asynchronous replication. In a truly synchronous cluster, where all data is kept consistent through 2-phase …

Working with replication, you come across many topologies, some of them sound and established, some of them less so, and some of them still in the realm of the hopeless wishes. I have been working with replication for almost 10 years now, and my wish list grew quite big during this time. In the last 12 months, though, while working at Continuent, some of the topologies that I wanted to work with have moved from the cloud of wishful thinking to the firm land of things that happen. My quest for star replication starts with the most common topology. One master, many slaves.

It looks like a star, with the rays extending from the master to the slaves. This is the basis of most of the replication going on mostly everywhere nowadays, and it has few surprises. Setting aside the …

We've been running replication poll and we've got some answers, so I thought I would comment a little on the results of the poll and what our future plans with respect to replication is as a result of the feedback. As I commented in the previous post, there are some items that require a significant development effort, but the feedback we got helps us to prioritize.

The top five items from the poll above stands out, so I thought that I would comment on each of them in turn. The results of the poll were (when this post were written):