The modifications include side effects like updating the access time that you might not ordinarily think of. Each NFS operation is processed within a database transaction. It uses PostGres as a storage device that it accesses by inode number, pathname and verset number. NFS operations counters are incremented. The NFS handle is broken into fields.
Inode numbers are unique across the entire database, even for identical files in different versets.
Each file in each verset has one database row. Whenever a shared file is modified, a private copy is made for that verset. This matches Pgfs' system administration orientation, where files will be large and binary and replaced in total, and the old and new binaries won't be similar enough to make differences small. This differs from source code, where the same files get incrementally modified over and over and differences are small. There is not a big delay while a compression algorithm unpacks intermediate versions into a temporary area.