HTH (even though it may be overly simplified),
Set

(*) In theory with the exception of 'borderline performance issues', were single field indexes are too slow, whereas multifield indexes are quick enough. Though I have to say that I work on smaller databases than you do and never have experienced this (I prefer simplicity over - let me make a wild guess - 20% performance improvement).

The last point is the essential 20% performance improvement

but i also know that Firebird do really good job on "bitmap or" and "bitmap and" operation on indexes, and it uses many indexes in one query very well.

 

regards,

Karol Bieniaszewski