Read operations on the database may request the return of modified but not yet committed data.

Provide for cursor stability but not repeatable reads. Data items which have been previously read by a transaction may be deleted or modified by other transactions before the original transaction completes.

For the life of the transaction, every time a thread of control reads a data item, it will be unchanged from its previous value (assuming, of course, the thread of control does not itself modify the item). This is Berkeley DB's default degree of isolation.