Andreas Joseph Krogh <andreas(at)visena(dot)com> writes:
> 1. Why isnt' folder_id part of the index-cond?
Because a GIN index is useless for sorting.
> 2. Is there a way to make it use the (same) index to sort by
> received_timestamp?
No.
> 3. Using a GIN-index, is there a way to use the index at all for sorting?
No.
> 4. It doesn't seem like ts_rank uses the index for sorting either.
Same reason.
regards, tom lane