A day with Paul McCullagh – Architect of PBXT and BlobStreaming

Continuing on from my lightning visits with Jan Kneschke and Michael Zinner, today I got to spend a day with Paul McCullagh at his home in Hamburg Germany.

Paul is the architect of the PBXT Pluggable Storage Engine for MySQL 5.1, and also the Blob Streaming Storage Engine. His work was acknowledged with the MySQL Community contributor for the year in 2007. The successful PrimeBase product for the publishing Industry in Europe and North America also now uses PBXT for underlying data storage which is great to see a company use it’s own products.

Like each friend and expert this week, Paul develops using Mac, but at least uses the US English version & keyboard layout, not the German layout. As Paul states, “the German version is not productive for coding”.

Paul uses NetNewsWire Lite as his RSS feeder, as I observe some PlanetMySQL links. I’m more old school, I just go to the site every few days. I really should move from the dark ages, one advantage is the RSS feeder shows you what you have read.

However, there is a particular reason why I visited Paul, other then to spend some time with a good friend. I’m doing more investigation regarding making coding changes to MySQL, and I’m very out of the development cycle. I’ve forgotten more then I remember with C++ and in particular the tools and techniques used to develop, debug and deploy. Of course I know what I need to do, I just need to know what now is the most efficient means of doing today.

Paul uses Xcode to view and edit his MySQL code. The development environment provided by Apple is good for Java and C++. As an Eclipse person from my Java days, I was using CDT for my C++ environment. XCode is used for project management (i.e. looking at files in project) and for file editing. A standard terminal is used to do make. Xcode can do a quick compile for syntax checking and you get a list of errors and hot links to lines of code.

The next key part is debugging, and you can very easily define executables and enable you to run in an integrated debugger. A good option testing is to run mysql test with is –manual-gdb. This gives you the command you can run. What Paul does it copy the parameters, and add to an executable defined within XCode, the arguments from the –manual-gdb output.

The MySQL source tree was added as a project but only partial source directories such as (storage,sql,include) are required. You do need to make sure it does compile (but necessary for a build via Xcode.)

Additional debugging help is In xcode you can do jump to variable definition. So you can add breakpoints, and then run the defined executable that was build via command line make, and copy mysqld binary to initially deployed directory.

Regarding testing, we got to talk again about the issues with the MySQL Test Suite including the issues I encountered while working with Nitro. Hard coded storage engine syntax such as such as engine type=Innodb make testing more complicated then necessary. MySQL test requires some modifications for pluggable storage engines. You need to add a row to the plugins table via mysql_system_tables_data.sql to enable –default-storage-engine=pbxt as a command line argument. Paul did state that on using the MySQL testing suite, the Perl version is a great improvement in performance.

So now I understand the environment, I get onto my problem, and we are specifically looking at the thread sort_buffer and sql/filesort.cc

So when I ask about a few lines of specific code, Paul shakes his head, and says “This looks crazy”. After we spend some time on it, his comment is upgraded, “this doesn’t look crazy, it is crazy. When you look at the effect of the code, it appears it can be done in 3 lines, and it would make sense what it is doing.” This is worth further discussion in a future post.

One last tip learned. You need to be careful with multiple versions and open projects of the same, not to make changes 1/2 in one version and 1/2 in another version.


  1. Diego says

    If you have a gmail account, google reader is a good option for RSS reader. (Computer independent and it keeps track of read articles)