Current Limitations
     
- The terms are not necessarily fetched in the same order as they
were stored.
     
 - If the process dies during an update operation (
db_store/3,
db_erase/[2,3]), the database can be inconsistent.
      - Databases can only be shared between processes running on the
machine where the environment is created (see Predicates).  The
database itself can be on a different machine.
     
 - The number of terms ever inserted in a database cannot
exceed 2^32-1.
     
 - Duplicate keys are not handled efficiently by Berkeley DB.  This
limitation is supposed to get lifted in the future.  Duplicate keys can
result from indexing on non-key attribute sets, inserting terms
with variables on indexing positions, or simply from storing the
same term more than once.