Updated msl (microslow) patch, installation walk-through!

For a couple of months there have been no updates to our msl patch, however recently I managed some time to change this. The functionality was extended a little bit and what’s even more important the patch is available for all the recent MySQL releases.

To remind anyone who has not yet come across this piece of code. msl (microslow) patch was developed a few years ago to allow more precise logging of query execution times into the slow log. Originally MySQL database offered a second time resolution and also a 2 second minimum for the query to get written, that is when you set long_query_time=1. After applying the patch you could see whether the time was 0.005s or 0.9s, which can make a substantial difference for the database and application performance. Over time msl patch grew with new features to let people learn more details of query execution, normally hidden from everyone’s eyes. Currently it’s used by many DBAs and developers to help in optimizations or troubleshooting the applications. We ourselves often rely on it when doing commercial MySQL consulting and MySQL AB has even adopted it into the official database distribution starting 5.1.21 release.

Below you will find the files to download, but first let me walk you through the installation and configuration because things changed along the way.


In order to use the patch first you will need to build the database binaries from source. This is unavoidable. Following this guide I hope should make it fairly easy even for those of you, who do not have much experience in that kind of tasks.

Of course the problem can be approached in many different ways, however I will be describing the method that is simple, non-intrusive to the system and additionally allows marginal database downtime. It should also work on virtually any Linux distribution and possibly under most other systems.

The patch is currently available for MySQL 5.0.45, 5.0.51a, 5.0.54a and 5.0.56. I assume you have some MySQL version installed already, but if it’s not any of these releases, you will need to upgrade (it will be worth it anyway :-)). You will also need to download the sources matching the installed database version. Once you have it all in place, we can begin.

Open command line (shell) on the server and go to the directory where the sources archive and the patch is. First you should determine how your current MySQL installation was built, so you can have the new binary to be as close to the original one as possible (e.g. to have the same set of storage engines or default paths):

From that output you can learn how to run configure command, which needs to be done prior to compiling the sources. It should be one long line full of various options and in the above case it was:

Take your output and copy&paste it to some notepad for later. Next step is to extract the archive:

Once that has completed, enter the sources directory:

Finally you can apply the patch:

Now it is the time to run configure with all the options you discovered earlier. Please do not use the below example as it may not be suitable for your environment.

This command will take about a minute to complete and it prints the following message at the end when everything goes fine:

Otherwise you will see some error. The sources have been prepared for compilation, so you are ready to run it:

Now it’s a good moment to go and get yourself a cup of tea, because for the next 5-10 minutes, depending on the hardware, you will be sitting idle and watching tons of text scrolling through the screen. The process should end with no errors and message like this one:

The new database binary should be now available in sql subdirectory:

If it’s not there, you had errors in compilation. You may strip the symbols off the binary to make it smaller: