QUERY PLAN ---------------------------------------------------------------------------------------------------------------------------------------------------------- Seq Scan on box b (cost=0.00..3669095.76 rows=128 width=8) (actual time=0.147..431517.693 rows=128 loops=1) SubPlan 1 -> Hash Anti Join (cost=14742.77..28664.79 rows=19239 width=8) (actual time=2960.176..3370.425 rows=1 loops=128) Hash Cond: (m1.box_id = m2.box_id) Join Filter: (m1.id < m2.id) -> Bitmap Heap Scan on message m1 (cost=544.16..13696.88 rows=28858 width=16) (actual time=2.320..6.204 rows=18487 loops=128) Recheck Cond: (box_id = b.id) -> Bitmap Index Scan on "message_box_Idx" (cost=0.00..536.94 rows=28858 width=0) (actual time=2.251..2.251 rows=18487 loops=128) Index Cond: (box_id = b.id) -> Hash (cost=13696.88..13696.88 rows=28858 width=16) (actual time=12.632..12.632 rows=19720 loops=120) Buckets: 4096 Batches: 4 (originally 2) Memory Usage: 1787kB -> Bitmap Heap Scan on message m2 (cost=544.16..13696.88 rows=28858 width=16) (actual time=1.668..6.619 rows=19720 loops=120) Recheck Cond: (box_id = b.id) -> Bitmap Index Scan on "message_box_Idx" (cost=0.00..536.94 rows=28858 width=0) (actual time=1.602..1.602 rows=19720 loops=120) Index Cond: (box_id = b.id) Total runtime: 431520.186 ms