Percona XtraDB Cluster (PXC) itself manages quorum and node failure.  Minorities of nodes in a network partition situation will move themselves into a Non-primary state and not allow any DB activity.  Nodes in such a state will be easily detectable via SHOW GLOBAL STATUS variables.

It’s common to use HAproxy with PXC for load balancing purposes, but what if you are planning to just send …

September 17, 2013 By Severalnines

Galera cluster has known limitations, one of them is that it uses cluster-wide optimistic locking. This may cause some transactions to rollback. With an increasing number of writeable masters, the transaction rollback rate may increase, especially if there is write contention on the same dataset. It is of course possible to retry the transaction and perhaps it will COMMIT in the retries, but this will add to the transaction latency. However, some designs are deadlock prone, e.g sequence tables. In this blog we present how you can minimize the risk for deadlocks due to the design of Galera. 

Test Case

Here is a simple test case. We have a table that contains a column and a row that hold a number and is regularly updated to provide …

A loadbalancer is used in many MySQL setups. Loadbalancing can be done with an hardware loadbalancer or with software. Software solutions tend to be a fair bit cheaper.

Loadbalancing is often implemented as an extra layer: The application connects to the loadbalancer via the network and the loadbalancer connects to the database via the network. The loadbalancing can be implemented on the application machines to get rid of the extra layer, this is better for latency (each layer adds latency) and as each application server has it's own loadbalancer it can also remove bottlenecks. The drawback are that you'll lose a single point of control and with multiple loadbalancers the number of health check queries will probably increase. The two-layer setup is often used with Connector/J and haproxy.

There are simple and more intelligent loadbalancers. There are loadbalancers which can split read and write traffic for example. Of …

The aim of this post is to enumerate real-world usage of Percona XtraDB Cluster (PXC), and also to solicit use cases from the readers. One of the prominent usages in the production environment that we have come across (and our Percona consultants have assisted) is that of HP Cloud. There is a post about it here by Patrick Galbraith of HP. The post focuses on their deployment of PXC for HP Cloud DNS. The post focuses on the key aspects of synchronous replication setup with high-availability guarantees like split-brain immunity.

Nobody likes to debug async replication while its broken or …

April 26, 2013 By Severalnines

This post shows you how to move from a single instance Drupal/MySQL to a multi-server environment. A well designed multi-server deployment not only allows Drupal to scale, but will also enhance redundancy by removing single points of failure. Components used are Apache, PHP, csync2, lsyncd, Keepalived, HAproxy, MySQL Galera Cluster and ClusterControl.

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This is a “dogfood” type story (see below for explanation of the term)… Open Query has ideas on resilient architecture which it teaches (training) and recommends (consulting, support) to clients and the general public (blog, conferences, user group talks). Like many other businesses, when we first started we set up our infrastructure quickly and on the cheap, and it’s grown since. That’s how things grow naturally, and is as always a trade-off between keeping your business running and developing while also improving infrastructure (business processes and technical).

Quite a few months ago we also started investing (mostly time) in the technical infrastructure, and slowly moving the various systems across to new servers and splitting things up along the way. Around the same time, the main webserver frequently became unresponsive. I’ll spare you the details, we know what the problem was and it was predictable, but since it wasn’t …

After the previous post in this caching related series I’ve received many questions on hardware and software configuration of our servers so in this post I’ll describe our server’s configs and the motivation behind those configs.

Hardware Configuration

Since in our setup Squid server uses one-process model (with an asynchronous requests processing) there was no point in ordering multi-core CPUs for our boxes and since we have a lots of pages on the site and the cache is pretty huge all the servers ended up being highly I/O bound. Considering these facts we’ve decided to use the following hardware specs for the servers:

CPU: One pretty cheap dual-core Intel Xeon 5148 (no need in multiple cores or really high frequencies – even these CPUs have ~1% avg load)
RAM: 8Gb (basically …