At 05:39 PM 11/29/2004, GrumpyRain wrote:

> You are right that Firebird indexes are
>one directional. My understanding is that this is to minimize the size
>of the index. The only drawback I can see is that the index can't help
>with a reverse sort, but you can always add a descending index if you
>need that functionality.

Actually, no, indexes are one-directional because that is
the necessary precondition for non-deadlocking internal
structures. Indexes are dynamic multi-user structures
that can - and do - change while they are in use. As long
as everyone takes locks in the same order, everything works.
If I have a lock on page 15, I can ask for handoff to page
16, knowing that the request won't cause a deadlock. Since
I have a lock on page 15 and page 15 points to page 16, I
can be sure that page 16 will still be valid after the
handoff.

Regards,


Ann