maxogden/dat — pull request #207 by ekg (2014-10-17 19:12:35+00:00)
Title: change log ids in data keys and current table

The addition of change log ids to the data keys (after the versions), will allow us to quickly extract the state of the data at particular point in the change log. This can be accomplished via a linear scan of the keys in the data table, requiring that the change id of a particular object is <= the target point in the log.

If we did not include this data alongside the data, we would be forced to complete a reconstruction of the dataset via the change log. This would complicate the process of rolling back particular subsets of the data to predetermined points in the history. Additionally, it wouldn't be possible to quickly determine the relative age of two objects, which has a number of possible applications in reproducibility and logging.

No functionality is yet tested which is based on the change ids, but the next step should be to implement a commit/checkout or checkpoint/rollback model on top of it.