The key Sleepycat people went on to write WiredTiger which was acquired by Mongo -- it has some interesting features: http://source.wiredtiger.com/2.6.1/index.h

The key Sleepycat people went on to write WiredTiger which was acquired by Mongo -- it has some interesting features: http://source.wiredtiger.com/2.6.1/index.html http://source.wiredtiger.com/2.6.1/index.html > WiredTiger supports row-oriented storage (where all columns of a row are stored together), column-oriented storage (where columns are stored in groups, allowing for more efficient access and storage of column subsets) and log-structured merge trees (LSM), for sustained throughput under random insert workloads. > WiredTiger includes ACID transactions with standard isolation levels and durability at both checkpoint and fine-grained granularity. > WiredTiger can be used as a simple key/value store, but also has a complete schema layer, including indices and projections.