I’ve recently worked with customers using replication rings with 4+ servers; several servers accepting writes. The idea behind this design is always the same: by having multiple servers, you get high availability and by having multiple writer nodes, you get write scalability. Alas, this is simply not true. Here is why.

High Availability

Having several servers is a necessary condition to have high availability, but it’s far from sufficient. What happens if for instance C suddenly disappears?

• The replication ring is broken, so updates from A and B will never go to D. D will then quickly become so out-of-date that it’s not going to be usable. But wait! A will no longer receive the updates from B so A …

InnoDB Memcached’s read only query performance in 5.7 has already achieved a remarkable 1.1 million QPS record. Now, the read only query bottleneck shifts to the memcached client itself. Thus anything that can batch the queries and shorten the query strings helps.

Multiple Get

In the new 5.7 InnoDB Lab Release, we add support for the “multi-get” option within InnoDB Memcached. This functionality enables users to send multiple keys in a single “get” command. In this way, for client-server communication, the package size is reduced as multiple keys are package within a single “get” call. For InnoDB, it will no longer need to start a transaction and open the table for each key if they are packaged …

In my last post, I learned in disappointing fashion that sometimes you need to start small and work your way up, rather than trying to put together a finished product. This go-round, I’ll talk about my investigation into disk IO.

In an effort to better understand the hardware I have and it’s capacities, I started off by just trying to get some basic info about the RAID controller and the disks. This hardware in particular is a Supermicro, with a yet unknown RAID controller and 16 4TB disks arranged in RAID 6. Finding out more disk and controller information was the first step. “hdparm -i” wasn’t able to give me much, nor was “cat /sys/class/block/sdb/device/{model,vendor}”. “dmesg” …

As many learning experiences do, this one also starts out “So I was working on a project at work and…”.  In this case, the end result is to try to run as many concurrent copies of MySQL on a single server as possible, maintaining real time replication each running differing data sets. To help with this, I sent out to do this on a server with 36 7200rpm 4GB SATA disks, giving me roughly 120TB of available space to work with.

This isn’t an abnormal type of machine for us. Sometimes you simply need a ton of disk space. There is a quirk with this particular machine that I’ve been told: the RAID controller has some issues with addressing very large virtual disks and I should create 2 60TB volumes and stitch them together with LVM. Easy enough: pvcreate both volumes, create a volume group and a logical volume out of it and viola: …

Computer science is like an enormous tool box you can rummage through whenever you have a problem to solve. Most of the tools are sturdy and practical, like algorithms for B-trees. Some are also elegant, like consistent hashing in Dynamo. Finally there are some tools that you never quite figure out even after years of reflection. That piece of steel you are looking at could be Excalibur. Or it could be a rusty knife.

The CAP theorem falls into the last category, at least for me.  It was a major topic in the blogosphere a few years ago and Google Trends shows steadily increasing interest in the term since 2010.  It's not my goal to explain CAP fully--a good informal description is …

Mon, 2014-10-06 07:24martinbrampton

How can we find extra ways to test MaxScale? It‘s now working its way through a beta program, heading for general release. As part of the team responsible for its development, I’ve been looking for ways to find obscure bugs. Several approaches are involved, including unit tests and system tests. But another thing we wanted to try was to put a real life application, written by other people, in front of MaxScale.

What’s it all about?

To recap, the role of MaxScale is to present itself to clients as if it were a single MariaDB or MySQL database. In reality, it’s nothing of the kind. Instead it is an ingenious mechanism for talking to some kind of database group - maybe a cluster, maybe a master-slave group, maybe some more esoteric combination of multiple databases. MaxScale can adopt a variety of strategies to decide which of the back end databases will receive any particular …

Have you donwloaded our latest eBook, Configuring MySQL for Performance? It offers simple advice on configuring the most important settings to maximize your MySQL performance.

Below are a couple tidbits:

The Default Storage Engine

The default_storage_engine setting is the engine used for tables that don’t specify an engine explicitly. This used to be MyISAM, but it’s changed to InnoDB more recently. This is a good thing; it’s the engine we’ve suggested as default for most use cases for years. Just check to ensure this is set as you desire. If you don’t know what engine to use, the right answer is probably InnoDB.

The Query Cache

The query cache (variables whose names begin query_cache ) should generally be disabled, unless you’re quite familiar with MySQL and its inner workings and know that it’ll help on your workload. You can find a lot of discussion online about the potential impacts …

This session describes how MySQL empowers the games at King, particularly how the explosive
growth of Candy Crush Saga was handled and how the constant high load is served. It discusses what makes King’s applications scale, what problems the company has solved, what it is currently solving, and what it will be solving tomorrow. As the presentation describes King’s architecture, it highlights its strengths; weaknesses; major pain points; and, of course, greatest successes.

Download presentation here
http://www.slideshare.net/TedWennmark/mysqlking

MySQL 5.6.21 was recently released (it is the latest MySQL 5.6, is GA), and is available for download here.

For this release, there was 1 “InnoDB Notes” and 1 “Functionality Added or Changed” bug fix (and 0 “Security Fix”), so not much there, but of course they should be noted:

1. InnoDB Note: The –skip-innodb option is now deprecated and its use results in a warning. It will be removed in a future MySQL release. This also applies to its synonyms (–innodb=OFF, –disable-innodb, and so forth).
2. Functionality Added: Internally, spatial data types such as Geometry are represented as BLOB values, so when invoked with the –hex-blob option, mysqldump now displays spatial values in hex. (Bug #43544, Bug …

This week I have been spending a little bit of time creating a module for Sysbench so that it can use libAttachSQL as a database driver. The reason for doing this is twofold:

1. Brian (my boss at HP's Advanced Technology Group) said now would be a good time to benchmark libAttachSQL
2. I really needed more than a few basic queries to shake out bugs in the library, and a benchmark is a good way to shove a few million through it

On the bug front, it did find a total of 5 bugs, a couple of them serious. Which is great, the more testing and bug finding the better. These have all been fixed in GitHub and will be part of the upcoming 0.5.0 release.

The Test Setup …