Yes. And if you remember i gave you the code with another oid mapping implementation, which avoids using big-integers and a bit more simpler (i hope).
The current Magma relies on the ".idx" file to lookup locations of objects in the objects.dat file. Since oids are allocated consecutively, the file only grows as much as the db allocates new oids.
Do you happen to remember; whether you had a new scheme for looking up location of objects in the objects.dat file, since I assume you can no longer allocate oids consecutively?