Galera replication for MySQL brings not only the new, great features to our ecosystem, but also introduces completely new maintenance techniques. Are you concerned about adding such new complexity to your MySQL environment? Perhaps that concern is unnecessarily.

I am going to present here some simple tips that hopefully will let fresh Galera users prevent headaches when there is the need to recover part or a whole cluster in certain situations. I used Percona XtraDB Cluster (project based on Percona Server and Galera library + MySQL extensions from Codership) to prepare this post, but most if not all of the scenarios should also apply to any solution based on MySQL+Galera tandem you actually chose, whether these are binaries from Codership, MariaDB Galera Cluster or …

September 1, 2014 By Severalnines

According to Forrester, a DBA in a large enterprise manages between 8 and 275 databases, with the industry average being 40 databases to a DBA. Larger databases usually require extra effort around tuning, backup, recovery and upgrade. Cloud, as well as automation and management tools can help improve the number of databases managed by one DBA.  

With that background, we were pretty excited to introduce support for management of single-instance MySQL and MariaDB databases in ClusterControl 1.2.6. The majority, if not all of the cluster users out there, use single-instance or master-slave replicated setups along their mission-critical …

I was talking with a Percona Support customer earlier this week who was looking for Galera data on Percona Cloud Tools. (Percona Cloud Tools, now in free beta, is a hosted service providing access to query performance insights for all MySQL uses.)

The customer mentioned they were already keeping track of some Galera stats on Cacti, and given they were inclined to use Percona Cloud Tools more and more, they wanted to know if it was already supporting Percona XtraDB Cluster. My answer was: “No, not yet: you can install agents in each node (the regular way in the first node, then …

I was talking with a Percona Support customer earlier this week who was looking for Galera data on Percona Cloud Tools. (Percona Cloud Tools, now in free beta, is a hosted service providing access to query performance insights for all MySQL uses.)

The customer mentioned they were already keeping track of some Galera stats on Cacti, and given they were inclined to use Percona Cloud Tools more and more, they wanted to know if it was already supporting Percona XtraDB Cluster. My answer was: “No, not yet: you can install agents in each node (the regular way in the first node, then …

August 18, 2014 By Severalnines

There are several ways to get ClusterControl installed on your database infrastructure, as described in the ClusterControl Quick Start Guide. One simple way is to use an installation script, install-cc.sh. This script automates the whole process, and is executed on the host where you want to install ClusterControl. By default, it assumes the host has internet connectivity during the installation process.

For users who are not able to have their ClusterControl hosts connect to the Internet during the installation, we have some good news! The installer script now supports offline installations.

Requirements

Prior to the offline …

August 12, 2014 By Severalnines

Moodle is an open-source e-learning platform (aka Learning Management System) that is widely adopted by educational institutions to create and administer online courses. For larger student bodies and higher volumes of instruction, moodle must be robust enough to serve thousands of learners, administrators, content builders and instructors simultaneously. Availability and scalability are key requirements as moodle becomes a critical application for course providers. In this blog, we will show you how to deploy and cluster moodle/web, database and file-system components on multiple servers to achieve both high availability and scalability. 

We are going to deploy moodle on top of GlusterFS clustered file system and MariaDB Galera Cluster 10. To eliminate any single point of failure, we will use three nodes to serve the application and database while the remaining two are used for …

August 7, 2014 By Severalnines

Deploying Galera Clusters across WAN environments might lead to concerns around data privacy and security - especially as more organisations are having to comply with national and international regulations. You would not want hackers eavesdropping or intercepting replication traffic. Encrypted replication hides what is sent between the Galera nodes, and makes sure each node is only communicating to the ones it trusts. But how expensive is encryption?

In this blog, we will show you how to encrypt the replication traffic between your Galera nodes. We will also look into the performance impact of this encryption.

Encrypted Replication

Galera supports SSL for the encryption of replication traffic. When encryption is enabled, Galera group communication and Incremental State Transfer (IST) happens over an SSL-encrypted …

Using GTID to attach an asynchronous Slave sounds promising. Lets have a look at the two existing GTID implementations and their integration with Galera.

GTID@MariaDB

There is one GTID used by the cluster and every node increments the common seqno by itself. This works well as long all transactions are replicated by Galera (simplified InnoDB). Because Galera takes care of the Commit Order of the transactions on all nodes. So having identical GTID/seqno from the start there are no problems.

  node1> show global variables like 'gtid_binlog_pos';
  +-----------------+---------+
  | Variable_name   | Value   |
  +-----------------+---------+
  | gtid_binlog_pos | 0-1-504 |
  +-----------------+---------+

  node2> show global variables like 'gtid_binlog_pos';
  +-----------------+---------+
  | Variable_name   | Value   |
  +-----------------+---------+
  | gtid_binlog_pos | 0-1-504 | …

Galera the synchronous Master-Master replication is quite popular. It is used by Percona XtraDB Cluster, MariaDB Galera Cluster and even patched MySQL binaries exist. Quite often you want to add a slave to a Galera Cluster. This is going to work quite well. All you need is at least configure log_bin, log_slave_updates and server_id on the designated Masters and attach your Slave.

GTID@MariaDB

Even you can use traditional (non GTID) replication. Using non GTID replication is a hassle. As you need to search for the right offset on the new Master to attach your Slave on.

Using GTID promises to be easier. As you simply switch to the new Master and the replication framework finds the new position based on the GTiD automatically.

As a fact we have two GTID implementations

• GTID@MySQL/Percona
• GTID@MariaDB

…

Monitoring flow control in a Galera cluster is very important. If you do not, you will not understand why writes may sometimes be stalled. Percona XtraDB Cluster 5.6 provides 2 status variables for such monitoring: wsrep_flow_control_paused and wsrep_flow_control_paused_ns. Which one should you use?

What is flow control?

Flow control does not exist with regular MySQL replication, but only with Galera replication. It is simply the mechanism nodes are using when they are not able to keep up with the write load: to keep replication synchronous, the node that is starting to lag instructs the other nodes that writes should be paused for some time so it does not get too far behind.

If you are not familiar with this notion, you should read this …