> Ewe. How expensive is scanning an index compared to the heap? Does
> anyone have figure on that in terms of I/O and time?
See this post for an example:
http://archives.postgresql.org/pgsql-performance/2006-02/msg00416.php
For my 200 million table, scanning the pk index took ~ 4 hours. And then
there are some more indexes...
So if the index has to be scanned completely, that's still too much.
Cheers,
Csaba.