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MySQL is gearing up with its own high-availability Group Replication solution

Do It Yourself

Article from ADMIN 39/2017

By Sven Lankes

Oracle recently introduced Group Replication as a trouble-free high-availability solution for the ubiquitous MySQL.

One important reason for the success of MySQL [1] is asynchronous replication, introduced in the 2001 release 3.23, which allows admins to set up replica instances (slaves) that receive all data changes from the master system. When MySQL only needs to read data, it can do so on a slave to reduce the load on the master.

Many admins were quick to use this replication method to promote one of the slaves to the master if the master server failed. In practice, users often suffered data loss because the slave was not up to date and the asynchronous transmission of changes caused backlogs of anything from a few seconds to several minutes.

MySQL v5.5 saw the introduction of semi-synchronous replication, in which the master waits until a change reaches one of the slaves (but not until it is applied). In the case of multiple concurrent write access, however, it comes at the expense of server throughput and is therefore rarely used.

Highly Available

MySQL has thus not been able to achieve true high availability with its on-board tools. In the community, Galera Cluster by Codership Oy, released under the GPLv2 [2], has enjoyed increasing popularity in recent years. It is based on a MySQL server and supports writing to each of the nodes – given that you have at least three servers.

Galera uses a group protocol to ensure that changes can be made on all nodes. If this is impossible because another user has changed the same data at the same time on another node, MySQL rolls back the transaction. In this case, the client needs to handle the error (e.g., by resending the queries).

Prompted by the popularity of Galera Cluster, Oracle reacted, publishing a stable release of the Group Replication plugin in September 2016 with MySQL Server 5.7.17 after no fewer than eight

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