Tracking MySQL slow queries with syslog-ng


Like me, you may have experiencied slow-down on your PHP/MySQL website, especially when using a crappy CMS (who said Joomla ? ;-)) and have been told “hey, the linux guy, please fix this”.
To be honest, I won’t fix anything as I’m neither a DBA or a developer, however, in this article we will set up an automatic e-mail reporting of slow queries processed by your MySQL server.

First, you’ll have to remove your old syslog server and replace it with something powerful (I mean: syslog-ng):

The default Debian configuration doesn’t log mail system messages into syslog (unlike default rsyslogd), I suggest fixing this first:
In /etc/syslog-ng/syslog-ng.conf, find the line

And add this one:

We need to ask MySQL to log slow queries (queries for which processing took more than NN seconds).
Edit /etc/mysql/my.cnf and uncomment the following lines:

We started investigating with long_query_time set to 5 seconds, but 1 is a decent value. I haven’t tried yet to use something lower than 1 sec but I guess that should work.

Restart mysql server.

Open /etc/syslog-ng/syslog-ng.conf again and add the following piece of configuration:

A little explanation:
First we define a new source of log file. MySQL has its own way of logging and doesn’t rely on syslog, so we need to track its own log file and ask our syslog to merge this logs.
Then we create a new destination similar to the default d_syslog (aka /var/log/syslog file) but with text refactoring (just to make it look like a real syslog entry).
After that, another destination: pipe into an homemade script that will send the lines by email (and text refactoring again).
Finally, associate the sources with the two destinations.

So, yes, we need to create that “mailing” script. Create a new file named /etc/syslog-ng/mail-alert-mysql-slow-query and fill it with:

I stole this script somewhere on syslog-ng’s mailing list and tweaked it a bit.
This script is a lot better because it handles a timeout before sending the email (see 0.1 in last line).
A full “slow query log” is written on several line. Thanks to this genius piece of Python script, only one email containing all of them will be send!

Set this file +x (chmod 755) and restart syslog-ng. Run tail -f /var/log/syslog and start a slow mysql query.
You should see something like this:


*UPDATE* 2012-10-22

After using this setup for a while, we discovered that most of alert sent during the night were irrelevant.
So here a quick patch to disable it from midnight to 8am:

*UPDATE* 2015-11-19

I made a slightly better version for another issue at work:

Also, in this case I decided to filter out messages within syslog-ng, which would probably be a lot more efficient than using re module in Python script.

Here is my configuration file:

OCF-Linux on Debian [Part I]

Hi there,

1. Introduction

My first blog post will be about getting hardware accelerated aes-128-cbc cipher on my ALIX board, running a Geode LX. This processor can only handle aes-128-cbc so it’s basically useless, unless you plan to configure every service to only use this specific cipher. Anyway, I’ll do it nevertheless !

Unlike VIA chips (padlock), the Geode doesn’t come with any native acceleration on Linux. It’s however possible using OCF (Open Crypto Framework) which has been ported from BSD to Linux. It’ll provide in-kernel hardware acceleration exported to userland using /dev/crypto device node.

2. Rebuilding Debian’s kernel with OCF-Linux patch

Sadly, OCF requiere little changes into the kernel and cannot (for now) be built as a module.

/!\ If you plan to build a 32 bits kernel from a 64 bits environment, use a 32 bits chroot !

Install a bunch of dependencies: 

Download and extract current Debian’s latest kernel: 

(If there’s a GPG sign error or something, run dpkg-source -x *.dsc)

Download latest OCF-Linux package:

Generate OCF kernel patch:

Let’s get started…

Bump Debian’s package ABI by editing debian/config/defines:

Copy OCF Linux kernel patch:

Create a quilt patch “series” file:
/!\ 3+alix.1 must be be the version according to debian/changelog.
In my example, package version is 3.0.0-3, mine will be 3.0.0-3+alix.1.

Install build dependencies (with some pbuilder’s magic!):

Clean and prepare the source package:

It will probably fails because the patch contains some “fuzz”. If so, go to debian/build/source, duplicate this directory, apply the patch, diff again and replace ocf-linux-26.patch). Run both commands again.

Create a new changelog entry:

Set target to UNRELEASED instead on unstable (first line).
Fill the changelog, here’s mine:

Setup the right kernel flavor (refer to official documentation on Debian’s wiki for more information):

Configure it!

Change CPU type to Geode LX/GX (will enable a few optimization, dunno if it really matters).
Enable OCF in kernel configuration but disable the following hardware chip drivers (they fail to build): Micronas 7108, cryptocteon, XP4xx, Kirkwood, Talitos and Hifn. AMD Geode doesn’t require any driver: upstream provide geode_aes kernel module which only need a way to be accessed from userland, so you may disable everything except cryptosoft (software fallback for unsupported ciphers) and crytodev (userland link).


Once you see linux-headers and linux-image deb package, you can stop the build by hitting Ctrl+c (generating documentation packages takes ages).

We need linux-headers-common as well:

That’s it for the kernel part…

Stay tuned !