Berkeley DB

Cursor Stability

In the absence of locking, no guarantees are made about the stability of cursors in different threads of control. However, the Btree, Queue, and Recno access methods guarantee that cursor operations, interspersed with any other operation in the same thread of control, will always return keys in order and will return each non-deleted key/data pair exactly once. Because the Hash access method uses a dynamic hashing algorithm, it cannot guarantee any form of stability in the presence of inserts and deletes unless locking is performed.

If locking was specified when the Berkeley DB environment was opened, but transactions are not in effect, the access methods provide repeatable reads with respect to the cursor. That is, a DB_CURRENT ...