My previous writings were mostly teoretical, so I wanted to give a more practical example, showing the actual state of the current code. I also wanted to show how I have tried to make the feature fit well into the existing replication features, without requiring the user to enable lots of options or understand lots of restrictions before being able to use it.

So let us start! We will build the code from lp:~maria-captains/maria/10.0-mdev26, which at the time of writing is at revision knielsen@knielsen-hq.org-20130214134205-403yjqvzva6xk52j.

First, we start a master server on port 3310 and put a bit of data into it:

    server1> use test;

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I got some very good comments/questions on my previous post on MariaDB global transaction ID, from Giuseppe and Robert (of Tungsten fame). I thought a follow-up post would be appropriate to answer and further elaborate on the comments, as the points they raise are very important and interesting.

(It also gives me the opportunity to explain more deeply a lot of interesting design decisions that I left out in the first post for the sake of brevity and clarity.)

On crash-safe slave

One of the things I really wanted to improve with global transaction ID is to make the replication slaves more crash safe with respect to their current replication state. This state is mostly persistently stored information about which event(s) were last executed on the slave, so that after a server restart the slave will know from  [Read more...]

The main goal of global transaction ID is to make it easy to promote a new master and switch all slaves over to continue replication from the new master. This is currently harder than it could be, since the current replication position for a slave is specified in coordinates that are specific to the current master, and it is not trivial to translate them into the corresponding coordinates on the new master. Global transaction ID solves this by annotating each event with the global transaction id which is unique and universal across the whole replication hierarchy.

In addition, there are at least two other main goals for MariaDB global transaction ID:

Make it easy to setup global transaction ID, and easy to provision a new slave into an existing replication hierarchy.

Fully support

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In my ongoing efforts to migrate my fun side projects and coding experiments from SVN to Git I’ve come across some of my favorite Python based apps – which are all available in their respective repos on BitBucket, as follows:

IRC Bot Commander

• What it does: it’s an IRC bot that takes commands and does your bidding on whichever remote server the bot is installed on.
• How it does it: the bot runs on whatever server you install it on, then it connects to the IRC server and channel you configured it to connect to and it waits for you to give it commands, then it execs the commands and returns the output to your IRC chat window.

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Unfortunately jQuery doesn’t come with default form validation to check for ip-addresses or subnet masking. So without a long winded explanation here’s the code. Just include this as a separate JS file like the rest of your page’s JS.

// 'ipv4': IPv4 Address Validator
$.validator.addMethod('ipv4', function(value) {
    var ipv4 = /^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$/;    
    return value.match(ipv4);
}, 'Invalid IPv4 address');

// 'netmask': IPv4 Netmask Validator
$.validator.addMethod('netmask', function(value) {
    var mask = /^[1-2]{1}[2,4,5,9]{1}[0,2,4,5,8]{1}\.
[0-2]{1}[0,2,4,5,9]{1}[0,2,4,5,8]{1}\.
[0-2]{1}[0,2,4,5,9]{1}[0,2,4,5,8]{1}\.
[0-9]{1,3}$/;    
    return value.match(mask);
}, 'Invalid IPv4 netmask');

You can use it like this.

$("#myform_here").validate({
    rules:{
	ipaddress:{

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As a follow up to the previous post about logstash, here are a couple of related init scripts for anyone implementing the OpenSource Log Analytics setup that is explained over at divisionbyzero. These have been tested on CentOS 6.3 and are based on generic RC functions from Redhat so they will work with Redhat, CentOS, Fedora, Scientific Linux, etc.

• Init script for ElasticSearch: located in the repo by clicking here – servicewrapper required
• Init script

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If you’ve ever used non-opensource code, or applications that you don’t have complete control over, then you may have run into situations you need to alter data on a per-row basis but been unable to do so for lack of application SQL access. The solution to this type of problem is to use a MySQL TRIGGER, which allows us to execute arbitrary SQL commands when defined events occur. Why is this useful and how does it work? Well…

For example, I have a freeRADIUS server that uses MySQL as a backend for the user authentication, and one of my server applications (HostBill) provides a freeRADIUS plugin that allows my users to manage their RADIUS accounts; however the default freeRADIUS schema lacks a DATETIME column on the user table. When a user is created (INSERT) or has their password changed (UPDATE)

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I write a fair number of scripts on this site and have posted a lot of code over the years. Generally if I am not pasting the code to be viewed on the webpage then I link to a file that a user can download; which leads to a lot of mish-mash code that doesn’t have a home. I’ve always kept the code files in a private SVN repo over the years but have recently moved them all to BitBucket Git repositories. So here they are: lots of code samples and useful bits of programming to save time.

Generic Shell Scripts: https://bitbucket.org/themattreid/generic-bash-scripts/src
Generic Python Scripts: https://bitbucket.org/themattreid/generic-python-scripts/src
Generic MySQL Stored Procs:

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I was digging through some old project code and found this script. Sometimes one finds oneself in an odd situation and needs to convert regular SQL, say from a MySQL database dump, into SQLite3 format. There’s not too much else to say, but here is a script that helps with the process. It can likely be improved but this handles the items that came up during conversion on initial runs.

#!/bin/sh
####
# NAME: convert-mysql-to-sqlite3.sh
# AUTHOR: Matt Reid
# DATE: 2011-03-22
# LICENSE: BSD
####
if [ "x$1" == "x" ]; then
   echo "Usage: $0 "
   exit 
fi 
cat $1 |
grep -v ' KEY "' |   
grep -v ' UNIQUE KEY "' |
grep -v ' PRIMARY KEY ' |
sed '/^SET/d' |          
sed 's/ unsigned / /g' | 
sed 's/ auto_increment/ primary key autoincrement/g' |
sed 's/ smallint([0-9]*) / integer /g' | 
sed 's/ tinyint([0-9]*) / integer /g' |  
sed 's/ int([0-9]*) / integer /g' |      
sed 's/

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If you’ve ever been troubleshooting on the MySQL command line and needed to quickly see how much memory is being used then you’ve probably noticed that there are no built in commands to give you this data. Unlike other enterprise databases MySQL doesn’t have a very robust management system built in to help make the DBA’s life easier. It doesn’t come with built in Stored Procedures to report on usage statistics or generate handy reports; so we have to code them and import them to MySQL — no relying on Oracle to help us out here.

So, here’s a stored procedure that can be imported to MySQL and run whenever you need to see the memory usage statistics. Installation and usage info is built into the SP below. The SP can also be downloaded from the repo:

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What do you think of this piece of C code?

  void foo(long v) {
    unsigned long u;
    unsigned sign;
    if (v < 0) {
      u = -v;
      sign = 1;
    } else {
      u = v;
      sign = 0;
    }
    ...

Seems pretty simple, right? Then what do you think of this output from MySQL:

  mysql> create table t1 (a bigint) as select '-9223372036854775807.5' as a;
  mysql> select * from t1;
  +----------------------+
  | a                    |
  +----------------------+
  | -'..--).0-*(+,))+(0( | 
  +----------------------+

Yes, that is authentic output from older versions of MySQL. Not just the wrong number, the output is complete garbage! This is my all-time favorite MySQL bug#31799. It was caused by code like the above C snippet.

So can you spot what is wrong with the code? Looks pretty simple, does it

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I found time to continue my previous work on group commit for the binary log in MariaDB.

In current code, a (group) commit to InnoDB does not less than three fsync() calls:

Once during InnoDB prepare, to make sure we can recover the transaction in InnoDB if we crash after writing it to the binlog.

Once after binlog write, to make sure we have the transaction in the binlog before we irrevocably commit it in InnoDB.

Once during InnoDB commit, to make sure we no longer need to scan the binlog after a crash to recover the transaction. Of

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SSH tunnels provide a very effective means to access remote services and applications. Not only does it provide encryption of data between hosts, but it allows you to route connections between a sequence of servers, thus chaining connections. A common use of this method is to provide encrypted connections to MySQL servers so that user accounts can be limited to only “localhost” privileges, yet accessed from remote workstations without having to run MySQL+SSL.

The concept is simple, for example let’s say you have three servers: localhost (your workstation in America), a server in Europe, and a server in Japan. You want to access Apache running on port 80 on the Japan server but because of firewall restrictions you cannot access port 80 remotely, and to make things more difficult the Japan server only allows SSH connections from the Europe server’s IP. We can

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A special extended edition of Tech Messages for 2011-09-21 through 2012-05-11:

• Understanding Linux CPU Load - when should you be worried?
• Performance Testing - Load Balancer SSL Stress Testing
  This is a great simple test. Thanks, Corey!
• Mosh: the mobile shell
• Twitter open sources its MySQL secret sauce
• Lab Overview
  This guy is serious about his lab!

Here are some quick and easy bash commands to solve every day problems I run into. Comment and leave some of your own if you like. I might update this post with new ones over time. These are just some common ones.

Iterate through directory listing and remove the file extension from each file
ls -1 | while read each; do new=`echo $each |sed 's/\(.*\)\..*/\1/'` && echo $new && mv "$each" "$new"; done

Output relevant process info, and nothing else
ps axo "user,pid,ppid,%cpu,%mem,tty,stime,state,command"| grep -v "grep" | grep $your-string-here

Setup a SOCKS5 proxy on localhost port 5050, to tunnel all traffic through a destination server
ssh -N -D 5050 username@destination_server'

Setup a SOCKS5 proxy via a remote TOR connection, using local port 5050 and remote TOR port 9050
ssh -L 5050:127.0.0.1:9050 username@destination_server'

Display text or code file

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Engineering cultures differ from shop to shop. I have been in the same culture for 13 years so I am not an expert on what all the different types are. Before that I was living in Dilbert world. The culture there was really weird. The ideas were never yours. It was always some need some way off person had. A DBA, a UI "expert" and some product manager would dictate what code you wrote. Creativity was stifled and met with resistance.

I then moved to the early (1998) days of the web. It was a start up environment. In the beginning there were just two of us writing code. So, we thought everything we did was awesome. Then we added some more guys. Lucky for us we mostly hired well. The good hires where type A personalities that had skills we didn't have. They challenged us and we challenged them. On top of that, we had a CEO who had been a computer hacker in his teens. So, he had just enough knowledge to

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In my previous post I explained why I believe the production of RPM and DEB packages should be more integrated with the rest of your development process. Now it's time to look into how you can put the RPM build scripts inside your main source code repository, and in particular how I did that to produce RPM packages for Drizzle.

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Last weekend I released rpm files for the latest Drizzle Fremont beta (announcement). As part of that work I've also integrated the spec file and other files used by the rpmbuild into the main Drizzle bzr repository (but not yet merged into trunk). In this post I want to explain why I think this is a good thing, and in a follow up post I'll go into what I needed to do to make it work.

(And speaking of stuff you can download, phpMyAdmin 3.5.0-alpha1 now supports Drizzle!)

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I found myself reading NoSQL is a Premature Optimization a few minutes ago and threw up in my mouth a little. That article is so far off base that I’m not even sure where to start, so I guess I’ll go in order.

In fact, I would argue that starting with NoSQL because you think you might someday have enough traffic and scale to warrant it is a premature optimization, and as such, should be avoided by smaller and even medium sized organizations.  You will have plenty of time to switch to NoSQL as and if it becomes helpful.  Until that time, NoSQL is an expensive distraction you don’t need.

Uhm… WHAT?!

I’ve spent more than a few years using MySQL and have been using some NoSQL systems for the last year or so in a fairly busy environment. And

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This is a tale of the bug lp:798213. The bug report has the initial report, and a summary of the real problem obtained after detailed analysis, but it does not describe the processes of getting from the former to the latter. I thought it would be interesting to document this, as the analysis of this bug was rather tricky and contains several good lessons.

Background

The bug first manifested itself as a sporadic failure in one of our random query generator tests for replication. We run this test after all MariaDB pushes in our Buildbot setup. However, this failure had only occured twice in several months, so it is clearly a very rare failure.

The first task was to try to repeat the problem and get some more data in the form of binlog files and so on. Philip kindly

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Quick update to the framework that was released yesterday; I’ve added automatic graph generation. I chose DyGraphs due to the quick ability to enable support – the HTML is very quick and simply loads the CSV data. It has the same zooming features of Highcharts without the JS overhead.

Now when you run a load test you will get (in the output directory) a mixture of files: the main cumulative CSV and HTML file for the hostname that was tested, and then one CSV and HTML per report variable that was tested. This means you don’t have to drag the main CSV file into an alternate program or spend time parsing out certain variables one at a time to generate specific graphs.  I’ve also added support for limiting output of SNMP variables (LOAD,CPU,MEM). Head over here and download the update: 

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It seems that everyone loves load testing these days. Problem is that everyone is using their own quick scripts, simple or complex, to drive their tests without the ability for other DBAs to duplicate those tests. Let’s say I write a great test and share my results and graphs on the blog – you want to run the same tests to see how your new DB servers compare in performance: this framework allows you to do that without duplicating any work or writing code. This is a basic release that will get the ball rolling. I’ve included some sample tests in the README file, so give them a try.

This codebase offers a user friendly framework for creating and visualizing MySQL database load test jobs. It is based around Sysbench, which is generally considered the industry standard load test application. The framework allows you to do the following:

standardize your tests

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This will just be a short reminder. If you're planning to create multiple-column indexes in MySQL, remember that the order of the columns matters. As the MySQL documentation points out, any "leftmost prefix of the index can be used." This means that the index can be used for any number of columns in a where clause as long as those columns are at the beginning of the index column list and in the same order.

I was recently reminded of this issue while debugging a performance problem. Adding a multiple-column index resulted in query performance improvement of 400% to 2,000%. Naturally, this result is highly specific to the problem we were trying to solve.