On Wed, Jan 29, 2014 at 4:17 PM, Дмитрий Шалашов <skaurus@xxxxxxxxx> wrote:
Thanks for the tip!Well, index is now used but...
Limit (cost=264291.67..264291.75 rows=31 width=50)
-> Sort (cost=264291.67..264292.80 rows=453 width=50)
Sort Key: added
-> Bitmap Heap Scan on feed (cost=1850.99..264278.18 rows=453 width=50)
Recheck Cond: ((active_id = user_id) AND (type = 1))
Filter: ((user_id + 0) = 7)
-> Bitmap Index Scan on feed_user_id_added_idx2 (cost=0.00..1850.88 rows=90631 width=0)
Ah, of course. It prevents the optimization you want, as well as the one you don't want.
This is getting very ugly, but maybe change the index to match the degenerate query:
"feed_user_id_added_idx3" btree ((user_id + 0), added DESC) WHERE active_id = user_id AND type = 1
Long term I would probably look into refactoring the table so that "active_id = user_id" is not a magical condition, like it seems to be for you currently. Maybe introduce a boolean column.
Cheers,
Jeff
