Why another database manager?

A friend asked me recently why I spent my time implementing a DBMS, when there are already a number of open source databases. It is a good question because clearly I am not breaking any new ground here. In fact, I find myself incapable of inventing great new technology. Most of what I am implementing is well known stuff. I am a software engineer, rather than a scientist, going by the definitions of engineers and scientists by C.A.R.Hoare. It seems that this project is pure self indulgence, when I could be spending my time more fruitfully, either contributing to projects like Apache Derby, or working on something more relevant.

I guess that if I am honest with myself, I have to admit that there is an element of self indulgence here. But there is also some utility. The knowledge I gain in the process is a benefit to me in my work life. But apart from that, I think that my DBMS implementation is better documented and easier to understand than other opensource implementations. This is for a couple of reasons:

1. I use well established algorithms, which are well documented in computer science literature. I am also putting more effort into documentation than is typical of many opensource projects.
   
2. The system is decomposed into well defined modules which are loosely coupled. I find most other implementations are far more integrated, and therefore difficult to understand. I have traded off performance and efficiency in favour of ease of understanding.

There are still no books that describe how to build a real DBMS, and also show you with real code how DBMS features such as transactions, locking, recovery, btrees, etc. work. The only book that comes close is Transaction Processing: Concepts and Techniques, but the sample code contained in this book is not complete. In some ways, my project provides a sample implementation of many of the techniques described in this book.

Finally, there is the question of pride. When I started this project many years ago in C++, I never thought I could do it. I had no training in this field, and no access to people who do this type of stuff at work. Having come this far, it seems a shame to give up.