Slow performance on very large library

I'm hoping to use Calibre to manage the metadata (JUST the metadata) for a very large number of books (on the order of a few million), but I find that as the number of entries increases, adding new entries gets slower and slower, eventually becoming so slow that it's unusable, well before reaching a million entries.

Note that most of the entries are empty. They have no formats associated with them.

Is Calibre appropriate for managing this amount of metadata, doing searches, meta-data updates, etc.?