By default, if EcoLab's Makefile detects the presence of Berkeley DB on your system, it will be used. Otherwise it use the ndbm API. If libgdbm and/or libgdbm_compat (the NDBM compatibility layer in GDBM) these will be added to the linker flags, otherwise it will assume that ndbm is available as part of the standard system library.
You can't mix and match database types. If you have some data stored
in one type, and need to access it using a different database type,
the utilities convtoNDBM and convtoBDB found in the util directory may
be useful.