Named snapshots

Accismus could possibly have the ability to create a named snapshots, list them, read them, and delete them. For example a named snapshot could be used as input to a map reduce job.

A really nice feature would be the ability to efficiently compute the difference between two named snapshots. ZFS supports a capability like this using merkle trees. Have this capability could make exporting data much simpler. A user could do something like the following
1. Create named snapshot snap1
2. wait
3. Create named snapshot snap2
4. Use map reduce to write diffs between snap1 and snap2
5. bulk import deltas into Accumulo table for query
6. Rename snap2 to snap1
7. goto 2

Named snapshots would prevent commited data that immediately precedes the snapshot from being garbage collected. At this point I am not sure how to efficiently compute the diffs between snapshots (w/o doing a full table scan).