-- Crown Task 4 — unified feed query (precompute parent path): visibility + keyset + Top-N in ONE plan
-- FeedCrownIT.crownUnifiedPlanStacksVisibilityKeysetAndTopN (seed 2000, viewer user008, page 1)
-- 읽기 포인트: 세 기법이 한 플랜에 재정렬(Sort) 없이 겹쳐 있다 —
--   (1) 가시성+keyset = feed_visible 커버링 인덱스의 Index Only Scan (viewer_id 조건, Heap Fetches 20),
--   (2) Top-N = 부모 20건당 ix_highlights_feed_items_created 로 top-3 index seek (Nested Loop = LATERAL),
--   (3) Sort 노드 없음 — 두 순서(부모 keyset·자식 created_at)가 모두 인덱스에서 나온다.

Nested Loop  (cost=0.56..271.10 rows=60 width=686) (actual time=0.036..0.092 rows=60 loops=1)
  Buffers: shared hit=65 read=2
  ->  Limit  (cost=0.28..1.84 rows=20 width=24) (actual time=0.025..0.028 rows=20 loops=1)
        Buffers: shared hit=1 read=2
        ->  Index Only Scan using ix_feed_visible on feed_visible  (cost=0.28..117.22 rows=1500 width=24) (actual time=0.025..0.027 rows=20 loops=1)
              Index Cond: (viewer_id = '9ed28556-7ab3-4f5a-b327-7e0dd9536bf8'::uuid)
              Heap Fetches: 20
              Buffers: shared hit=1 read=2
  ->  Limit  (cost=0.28..13.42 rows=3 width=670) (actual time=0.003..0.003 rows=3 loops=20)
        Buffers: shared hit=64
        ->  Index Scan using ix_highlights_feed_items_created on highlights h  (cost=0.28..48.47 rows=11 width=670) (actual time=0.002..0.003 rows=3 loops=20)
              Index Cond: (feed_item_id = feed_visible.feed_item_id)
              Buffers: shared hit=64
Planning:
  Buffers: shared hit=11 read=1
Planning Time: 0.122 ms
Execution Time: 0.120 ms