Hello, I have a big table (around 3 600 000 entries) which stores which user has seen which subjects in a forum. This query is executed every time a user connects to the forum: SELECT flg_rid FROM prj_frm_flg WHERE flg_mid=3 AND NOT flg_fav AND NOT flg_notif AND NOT flg_post ORDER BY flg_rid DESC OFFSET 999 This query very often takes a lot of time to do its job (40-60s). I have a primary key on flg_mid and flg_sid (simultaneously) and indexes on flg_notif, flg_post and flg_fav. This is the result of an EXPLAIN: "Limit (cost=453.48..453.48 rows=1 width=4)" " -> Sort (cost=453.25..453.48 rows=94 width=4)" " Sort Key: flg_rid" " -> Bitmap Heap Scan on prj_frm_flg (cost=5.55..450.17 rows=94 width=4)" " Recheck Cond: (flg_mid = 3)" " Filter: ((NOT flg_fav) AND (NOT flg_notif) AND (NOT flg_post))" " -> Bitmap Index Scan on prj_frm_flg_pkey (cost=0.00..5.53 rows=117 width=0)" " Index Cond: (flg_mid = 3)" I suppose that the problem comes from the Bitmap Heap Scan which costs a lot, but I can't be totally sure. Any idea on where I should be investigating ? Thanks a lot. Mat.
