> We may be able to do the same thing with long strings. Firebird 2
> doesn't need to limit the index key at all, just truncate it at the
> maximum length that can be supported for the current page size, after
> the key is built, but before prefix compression.

Alternatively, FB2 has expression indexes. With it users can
exactly define its own truncation rules for long keys. Its can be
simple SUBSTRING, but it also can be some kind of hashing - all
depends on use cases which only database developers knows.

Regards,
Vlad