Showing entries 1 to 9
Displaying posts with tag: Varia (reset)
WebScaleSQL 5.6.24 is built and ready to test

On Tuesday  Steaphan Greene  announced that all currently-pushed changes have now been rebased onto the newly-released upstream MySQL-5.6.24.

The new branch at this point is available on github.

Our .deb and .rpm builds are available in the PSCE repo as well as being browsable here

Instructions for using the repo are available for Debian …

[Read more]
MySQL Character encoding – part 2

In MySQL Character encoding – part 1 we stated that the myriad of ways in which character encoding can be controlled can lead to many situations where your data may not be available as expected.

UTF8 was designed on a placemat in a New Jersey diner one night in September or so 1992.

Setting MySQL Client and Server Character encoding.

Lets restart MySQL with the correct setting for our purpose, UTF8. Here we can see the setting in the MySQL configuration file, in this case /etc/mysql/my.cnf.

character-set-server = utf8

This change is then reflected in the session and global variables once the instance is restarted with the new configuration parameter.

mysql> SELECT …
[Read more]
MySQL Character encoding – part 1

Breaking and unbreaking your data

Recently at FOSDEM, Maciej presented “Breaking and unbreaking your data”, a presentation about the potential problems you can incur regarding character encoding whilst working with MySQL. In short, there are a myriad of places where character encoding can be controlled, which gives ample opportunity for the system to break and for text to become unrecoverable.

The slides from the presentation are available on slideshare.

Character Encoding – MySQL DevRoom – FOSDEM 2015 from

[Read more]
WebScaleSQL RPMs available at PSCE repository

Driven by popularity of previous post about Debian/Ubuntu builds of WebScaleSQL and long discussions during FOSDEM conference this weekend, PSCE engineering team decided to put even more effort into.

We would like to introduce:

  • RPM packages available for download
  • RedHat/CentOS repository

Architectures covered:

  • x86 (32-bit)
  • x86_64 (64-bit)

Please note that “WebScaleSQL does not currently maintain compatibility for anything except GNU/Linux x86_64.” (WebScaleSQL FAQ)”

RedHat/CentOS releases:

  • CentOS 6
  • CentOS 7

Packages can be downloaded from …

[Read more]
WebScaleSQL builds for the MySQL Community

We have been looking at the WebScaleSQL project with great excitement. As with any new enhancements to the MySQL world, we need to test extensively to ensure we can give PSCE customers the best advice possible. Since this project is source only, we decided to add WebScaleSQL builds to our repo, so we could examine the changes being introduced by all the different collaborators.

So what is WebscaleSQL?

WebScaleSQL is a collaboration among engineers from several companies that face the same challenges in deploying MySQL at scale, and seek greater performance from a database technology tailored for their needs.

— WebScaleSQL, Frequently Asked Questions

What makes this project so special, is the level of collaboration between some of the most …

[Read more]
MySQL and the GHOST: glibc gethostbyname buffer overflow

Qualys announced they had found an exploit in one of the Linux core libraries – glibc – using a buffer overflow technique in gethostbyname(). They have developed a proof-of-concept in which simply sending a specially created e-mail to a mail server enabled them to create a remote shell to the Linux machine. According to Qualys, “This bypasses all existing protections (like ASLR, PIE and NX) on both 32-bit and 64-bit systems.”. How does it affect MySQL servers? Read on!

The vulnerable library call provides DNS name resolution and although it’s been obsoleted in favour of other calls, it is still widely used by both legacy and modern applications.

Having a quick search, MySQL does not seem to rely on gethostbyname() almost at all. A few uses can be found in MySQL Cluster code (NDB), …

[Read more]
Syncronizing MySQL where tables have triggers and foreign keys defined

On a recent consulting engagement, the PSCE team were charged with what can be considered a fairly common task of synchronising tables between master and slave in MySQL Replication. On this occasion the  schema contained both foreign key constraints and triggers, this post describes how we avoided the potential problems related to such an operation.

The process to synchronise tables in MySQL is to first identify the differences between tables and then execute queries which bring those tables into a consistent state. The first part of the process can be handled by the pt-table-checksum tool, which steps through the table analysing sets of rows (chunks) and recording a checksum value. Then taking advantage of replication, the same process occurs on each of the slaves and the checksums can then be compared. Once the entire table has been processed, a second tool pt-table-sync can be used …

[Read more]
And Now for Something Completely Different

As many of you may know the 2012 UEFA European Football Championship is just around the corner1. For the occasion I developed a web-based betting game to introduce a little bit of competition between me and my friends as well as make the Championships even more exciting. But then I thought “Hey, why not to do this for a bigger community as well”? So dear MySQLers, I invite you to join the special edition of my game here at dba square!

The game is available at or you can simply get there from the blog’s main menu at the top of each page.

We are offering you:

  • a little bit of fun
  • a free gambling opportunity
  • some friendly competition

The game is simple and works similarly to the real sports bookmaking, although there is …

[Read more]
A small rant on Galera & XtraDB Cluster

I had to install Percona XtraDB Cluster, I think for the first time since it was announced stable. I remembered many problems I faced with beta releases, which was understandable given they were only for a preview, but this time I hoped for significant improvements.

I have to say I am generally quite sensitive about simple problems that could/should be easily discovered and corrected. Well, it didn’t take five minutes to see a few of such problems. These minutes I spent installing the database binaries from Percona Yum repository. It turned out that was enough to see a lot of errors for no reason. Not a good thing.

  Installing : 1:Percona-XtraDB-Cluster-server-5.5.23-23.5.333.rhel6.x86_64         5/5
ls: cannot access /var/lib/mysql/*.err: No such file or directory
ls: cannot access /var/lib/mysql/*.err: No such file or directory
[Note] Flashcache bypass: disabled

Why does it matter that ls: cannot access …

[Read more]
Showing entries 1 to 9