SimpleDBM update

SimpleDBM project work has been slow for the past couple of months. This is because I have decided to develop SimpleDBM as a plug-in storage engine for Apache Derby, as an alternative to the Derby Store implementation. If anyone is interested in tracking this work, please visit the Apache JIRA system and look for DERBY-3351.

There are a few problems to be overcome for this to happen. One of this is to make some changes to Derby so that the Store components can be easily replaced. The good news is that Derby is already very modular, and its original design was intended to allow using the Store implementation on its own. I am working on improving the modularity of Derby, and to reduce dependencies between the layers. This work is likely to take several months or even the whole of this year.

The other main hurdle is that there are some fundamental differences in the design approaches taken by SimpleDBM and Derby.

Principal amongst these is that SimpleDBM treats Row and Index data as transparent blobs. This is an attempt to allow higher level implementations to choose their own row/index formats. In Derby, the row structure and the type system is known to the Storage Engine. The former approach is more flexible, but adds performance overheads. At present, my thinking is that to interoperate with Derby, I may have to adopt the Derby type-system.

Another fundamental design choice is the way modules plug into each other. In SimpleDBM, a constructor based injection pattern is used. The modules themselves do not decide how to obtain references to other modules. Derby allows each module to obtain reference to other modules via an intermediary, the Monitor.

SimpleDBM does not use static data in any way. Even the core of the system that instantiates objects, uses a dynamic lookup mechanism (ObjectRegistry) to map type codes to class types. Derby on the other hand, uses a fair number of static constructs. The Monitor system and the Context Manager are two key examples.

There are other areas of incompatibility. In the end, I do not know if this experiment will succeed in the way I would like it to.