Store snapshots in 2 layers.

[mornfall]

The base snapshot would change rarely or never, the 'normal' snapshot would only contain a delta on top of the (slow-changing) baseline. Let dios be in charge of deciding when this baseline snapshot is taken or updated. This is a compromise over automatic, variable-length delta chain encoding, which appears to be too expensive and makes it hard to come up with good heuristics.

Since the baseline snapshots would change only rarely, there would be few of them and we can possibly store them in a linear array, without hash tables and with very little indirection.