In a word: The kind of problems people use Berkeley DB for. People use BDB for more fine grained cursor access to BTrees. Stuff you CANNOT do with SQL. There is a market for this. See their website. I'd like something similar from Postgres so that the data would be stored in a full fledged RDBMS but I could use the cursor methods for searching more efficient than SQL. Best of both worlds. I've had a quick browse around the Postgres code and found some functions like "_bt_first()" but no sample code to use it. BTW its for developing an alternative server based access to the underlying relational data.
