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)
Dmitriy Shalashov
2014-01-30 Jeff Janes <jeff.janes@xxxxxxxxx>
On Wed, Jan 29, 2014 at 3:38 PM, Дмитрий Шалашов <skaurus@xxxxxxxxx> wrote:
"feed_user_id_added_idx2" btree (user_id, added DESC) WHERE active_id = user_id AND type = 1...SELECT * FROM feed WHERE user_id = ? AND type = 1 AND active_id = user_id ORDER BY added DESC LIMIT 31;
But it doesn't use the last index. EXPLAIN shows this:
Limit (cost=0.00..463.18 rows=31 width=50)
-> Index Scan Backward using feed_user_id_active_id_added_idx on user_feed (cost=0.00..851.66 rows=57 width=50)
Index Cond: ((user_id = 7) AND (active_id = 7))
Filter: (type = 1)So as we can see optimiser changes "active_id = user_id" to "active_id = <whatever value user_id takes>". And it brokes my nice fast partial index :(
Can I do something here so optimiser would use the feed_user_id_added_idx2 index? It's around ten times smaller than the 'generic' feed_user_id_active_id_added_idx index.How about "where user_id+0=?"Cheers,Jeff
