gistfile1.txt

SELECT  "statuses"."id", "statuses"."updated_at" FROM "statuses" 
WHERE "statuses"."account_id" = 1 AND ("statuses"."visibility" IN (0,1,2) OR exists(select id from mentions where mentions.account_id = 1867 and mentions.status_id = statuses.id))
ORDER BY "statuses"."id" DESC LIMIT 40;

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Analyze

Limit  (cost=0.43..497.99 rows=40 width=16) (actual time=0.079..1.090 rows=40 loops=1)
  ->  Index Scan Backward using index_statuses_on_account_id_id on statuses  (cost=0.43..5398.96 rows=434 width=16) (actual time=0.076..1.036 rows=40 loops=1)
        Index Cond: (account_id = 1)
        Filter: ((visibility = ANY ('{0,1,2}'::integer[])) OR (alternatives: SubPlan 1 or hashed SubPlan 2))
        Rows Removed by Filter: 1
        SubPlan 1
          ->  Index Only Scan using index_mentions_on_account_id_and_status_id on mentions  (cost=0.42..8.45 rows=1 width=0) (never executed)
                Index Cond: ((account_id = 1867) AND (status_id = statuses.id))
                Heap Fetches: 0
        SubPlan 2
          ->  Index Only Scan using index_mentions_on_account_id_and_status_id on mentions mentions_1  (cost=0.42..96.50 rows=60 width=8) (actual time=0.226..0.272 rows=23 loops=1)
                Index Cond: (account_id = 1867)
                Heap Fetches: 4
Planning time: 0.310 ms
Execution time: 1.426 ms