This is all with FB 1.0x.

1. If I have a set of unique values indexed, does making the INDEX
explicitly UNIQUE change the performance of inserts at all? Or does it
just add an explicit constraint to keep the index unique? Didn't know if
adding UNIQUE maybe allowed Firebird to use a more optimal BTree page
structure.

2. If I want to index on a column with a lot of dupes and I have a
unique numeric column in that field, what does it buy me to make this
index compound and add the unique numeric column as the second key in
the index? Does it impact query or insert performance or does it just
impact the performance of deletes?

3. I've heard that Firebird will always use the first key of a compound
index if there is not a separate index for the first key. IOW, if I have
an index on FOO, BAR that I don't need a separate index on FOO. However,
I have found that with certain joined queries that the optimizer will
use the index on FOO if it exists but will not use the FOO+BAR index.
Any thoughts?

Thanks!!!