-- L16 (a) single OR — the naive visibility filter: BitmapOr + top-N Sort + hashed SubPlan
-- FeedVisibilityIT.l16ExplainThreeWayPlanCompare (seed 2000, viewer user008)
-- SELECT fi.id, fi.first_highlighted_at FROM feed_items fi
--   WHERE (fi.visibility='PUBLIC'
--       OR (fi.visibility='MENTIONED' AND EXISTS(SELECT 1 FROM feed_item_mentions m WHERE m.feed_item_id=fi.id AND m.mentioned_user_id=:me))
--       OR (fi.visibility='PRIVATE' AND fi.user_id=:me))
--   ORDER BY fi.first_highlighted_at DESC, fi.id DESC LIMIT 20
-- 읽기 포인트: seq scan 이 아니라 BitmapOr(3분기 인덱스)로 후보 1500 을 heap scan → top-N Sort(순서 손실)
--            + 멘션 EXISTS 는 hashed SubPlan(후보마다 반복 아님). buffers shared hit=122.

Limit  (cost=224.45..224.49 rows=15 width=24) (actual time=0.713..0.716 rows=20 loops=1)
  Buffers: shared hit=122
  ->  Sort  (cost=224.45..224.49 rows=15 width=24) (actual time=0.712..0.713 rows=20 loops=1)
        Sort Key: fi.first_highlighted_at DESC, fi.id DESC
        Sort Method: top-N heapsort  Memory: 26kB
        Buffers: shared hit=122
        ->  Bitmap Heap Scan on feed_items fi  (actual time=0.256..0.590 rows=1500 loops=1)
              Recheck Cond: ((visibility='PUBLIC') OR (visibility='MENTIONED') OR ((user_id=:me) AND (visibility='PRIVATE')))
              Filter: ((visibility='PUBLIC') OR ((visibility='MENTIONED') AND (hashed SubPlan 2)) OR ((visibility='PRIVATE') AND (user_id=:me)))
              Rows Removed by Filter: 200
              Buffers: shared hit=122
              ->  BitmapOr  (actual time=0.185..0.185 rows=0 loops=1)
                    ->  Bitmap Index Scan on ix_feed_items_visibility_sort  (Index Cond: visibility='PUBLIC')   rows=2400
                    ->  Bitmap Index Scan on ix_feed_items_visibility_sort  (Index Cond: visibility='MENTIONED') rows=800
                    ->  Bitmap Index Scan on ix_feed_items_private          (Index Cond: user_id=:me)           rows=100
              SubPlan 2
                ->  Bitmap Heap Scan on feed_item_mentions m  (Recheck Cond: mentioned_user_id=:me)  rows=200
                      ->  Bitmap Index Scan on ix_mentions_user  (Index Cond: mentioned_user_id=:me)  rows=200
Planning Time: 0.144 ms
Execution Time: 0.808 ms