Buffer Internals

Finally the asynchronous support has been completed. :-D and as a result the BufferDevice hierarchy is far simpler and the PageDevice hierarchy is also far flatter.

So now I have two class hierarchies - one deals with buffers and can be considered the low-level API and the other deals with pages and can be considered the next level up the chain. The buffer handlers were surprisingly easy to write - more a question of moving code from various other classes which was made a nice change.

The page classes were also surprisingly straightforward especially given the fact that I chopped lots and lots of classes out!!

The real pain came when I decided to unravel the state machine for buffer objects - this turned into a week-long adventure but the result is an incredibly flexible finite-state-machine which ensures consistent buffer state transitions and proper state handling without littering the Buffer class with lots of boolean flags! This task was necessary in order to make the object fully asynchronous...

The buffer can now support the following async operations;

• Read From Device Stream


• Write To Device Stream


• Write To Log Device

With this support in buffers and their corresponding devices complete, attention now turns to pages and their devices. There are a couple of loose ends which still need to be tied up with regard to hand off and lock acquisition - I also need to ensure the transaction handler will correctly unlock pages during the commit phase...

Finally the outer DatabaseDevice device can be completed with regard to recovery and the final mounting procedure before I once again fix the installer classes (and use them to test the initial portion of the codebase).