Hi, I'm using PostgreSQL 14.3 and I'm getting strange behavior in a complex query generated by the Entity Framework.
The inner (complex) query has a quick execution time: # SELECT "Extent1"."id", CAST ("Extent1"."date" AS timestamp) AS "C3" FROM "dbo"."ng_content" AS "Extent1" INNER JOIN "dbo"."ng_path_content" AS "Extent2" ON "Extent1"."id" = "Extent2"."id_content" WHERE "Extent1"."date_from" <= CAST (LOCALTIMESTAMP AS timestamp) AND "Extent1"."date_to" >= CAST (LOCALTIMESTAMP AS timestamp) AND 2 = "Extent1"."id_status" AND EXISTS ( SELECT 1 AS "C1" FROM ( SELECT "Extent3"."TagId" FROM "dbo"."ngx_tag_content" AS "Extent3" WHERE "Extent1"."id" = "Extent3"."ContentId" ) AS "Project1" WHERE EXISTS ( SELECT 1 AS "C1" FROM (SELECT 1 AS "C") AS "SingleRowTable1" WHERE "Project1"."TagId" = 337139) ) AND ("Extent2"."id_path" IN (27495,27554,27555) AND NOT EXISTS (SELECT 1 AS "C1" FROM (SELECT 1 AS "C") AS "SingleRowTable2" WHERE TRUE = FALSE) ); id | C3 ----------+--------------------- 13505155 | 2021-03-27 12:01:00 13505187 | 2021-03-27 12:03:00 13505295 | 2021-03-27 12:06:00 13505348 | 2021-03-27 12:09:00 13505552 | 2021-03-27 12:11:00 (5 rows) *Time: 481.826 ms* If I run the same query as a nested select I get similar results (Q1): *SELECT "Project5".idFROM (* SELECT "Extent1"."id", CAST ("Extent1"."date" AS timestamp) AS "C3" FROM "dbo"."ng_content" AS "Extent1" INNER JOIN "dbo"."ng_path_content" AS "Extent2" ON "Extent1"."id" = "Extent2"."id_content" WHERE "Extent1"."date_from" <= CAST (LOCALTIMESTAMP AS timestamp) AND "Extent1"."date_to" >= CAST (LOCALTIMESTAMP AS timestamp) AND 2 = "Extent1"."id_status" AND EXISTS ( SELECT 1 AS "C1" FROM ( SELECT "Extent3"."TagId" FROM "dbo"."ngx_tag_content" AS "Extent3" WHERE "Extent1"."id" = "Extent3"."ContentId" ) AS "Project1" WHERE EXISTS ( SELECT 1 AS "C1" FROM (SELECT 1 AS "C") AS "SingleRowTable1" WHERE "Project1"."TagId" = 337139) ) AND ("Extent2"."id_path" IN (27495,27554,27555) AND NOT EXISTS (SELECT 1 AS "C1" FROM (SELECT 1 AS "C") AS "SingleRowTable2" WHERE TRUE = FALSE) ) *) AS "Project5";* id ---------- 13505155 13505187 13505295 13505348 13505552 (5 rows) *Time: 486.174 ms* But if I add an ORDER BY and a LIMIT something goes very wrong (Q2): # SELECT "Project5".id FROM ( SELECT "Extent1"."id", CAST ("Extent1"."date" AS timestamp) AS "C3" FROM "dbo"."ng_content" AS "Extent1" INNER JOIN "dbo"."ng_path_content" AS "Extent2" ON "Extent1"."id" = "Extent2"."id_content" WHERE "Extent1"."date_from" <= CAST (LOCALTIMESTAMP AS timestamp) AND "Extent1"."date_to" >= CAST (LOCALTIMESTAMP AS timestamp) AND 2 = "Extent1"."id_status" AND EXISTS ( SELECT 1 AS "C1" FROM ( SELECT "Extent3"."TagId" FROM "dbo"."ngx_tag_content" AS "Extent3" WHERE "Extent1"."id" = "Extent3"."ContentId" ) AS "Project1" WHERE EXISTS ( SELECT 1 AS "C1" FROM (SELECT 1 AS "C") AS "SingleRowTable1" WHERE "Project1"."TagId" = 337139) ) AND ("Extent2"."id_path" IN (27495,27554,27555) AND NOT EXISTS (SELECT 1 AS "C1" FROM (SELECT 1 AS "C") AS "SingleRowTable2" WHERE TRUE = FALSE) ) ) AS "Project5" *ORDER BY "Project5"."C3" DESC LIMIT 6*; id ---------- 13505552 13505348 13505295 13505187 13505155 (5 rows) *Time: 389375.374 ms (06:29.375)* An EXPLAIN (ANALYZE, BUFFERS) for Q1 returns this: QUERY PLAN --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Result (cost=661.07..826757.96 rows=27943 width=4) (actual time=446.767..492.874 rows=5 loops=1) One-Time Filter: (NOT $1) Buffers: shared hit=344618 read=17702 written=349 InitPlan 2 (returns $1) -> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.003..0.003 rows=0 loops=1) One-Time Filter: false -> Nested Loop (cost=661.07..826757.96 rows=27943 width=4) (actual time=267.061..313.166 rows=5 loops=1) Buffers: shared hit=344618 read=17702 written=349 -> Bitmap Heap Scan on ng_path_content "Extent2" (cost=660.63..30053.47 rows=58752 width=4) (actual time=2.455..28.005 rows=51330 loops=1) Recheck Cond: (id_path = ANY ('{27495,27554,27555}'::integer[])) Heap Blocks: exact=2914 Buffers: shared hit=5 read=2963 written=35 -> Bitmap Index Scan on ng_path_content_id_path_idx (cost=0.00..645.94 rows=58752 width=0) (actual time=2.020..2.021 rows=51332 loops=1) Index Cond: (id_path = ANY ('{27495,27554,27555}'::integer[])) Buffers: shared hit=5 read=47 -> Index Scan using pk_ng_content on ng_content "Extent1" (cost=0.43..13.55 rows=1 width=4) (actual time=0.005..0.005 rows=0 loops=51330) Index Cond: (id = "Extent2".id_content) Filter: ((2 = id_status) AND (date_from <= LOCALTIMESTAMP) AND (date_to >= LOCALTIMESTAMP) AND (SubPlan 1)) Rows Removed by Filter: 1 Buffers: shared hit=344613 read=14739 written=314 SubPlan 1 -> Index Only Scan using ix_ngx_tag_content on ngx_tag_content "Extent3" (cost=0.43..8.46 rows=1 width=0) (actual time=0.001..0.001 rows=0 loops=51327) Index Cond: (("TagId" = 337139) AND ("ContentId" = "Extent1".id)) Heap Fetches: 5 Buffers: shared hit=153982 read=4 Planning: Buffers: shared hit=464 read=87 written=51 Planning Time: 5.374 ms JIT: Functions: 18 Options: Inlining true, Optimization true, Expressions true, Deforming true Timing: Generation 1.678 ms, Inlining 81.653 ms, Optimization 63.837 ms, Emission 33.967 ms, Total 181.135 ms Execution Time: 534.009 ms (33 rows) An EXPLAIN (ANALYZE, BUFFERS) for Q2 returns this: QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Limit (cost=0.88..8979.75 rows=6 width=12) (actual time=11037.149..183849.138 rows=5 loops=1) Buffers: shared hit=15414548 read=564485 written=504 InitPlan 2 (returns $1) -> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.000..0.001 rows=0 loops=1) One-Time Filter: false -> Result (cost=0.86..41816103.19 rows=27943 width=12) (actual time=11037.146..183849.127 rows=5 loops=1) One-Time Filter: (NOT $1) Buffers: shared hit=15414548 read=564485 written=504 -> Nested Loop (cost=0.86..41816103.19 rows=27943 width=12) (actual time=11037.143..183849.116 rows=5 loops=1) Buffers: shared hit=15414548 read=564485 written=504 -> Index Scan Backward using ix_ng_content_date on ng_content "Extent1" (cost=0.43..40616715.85 rows=2231839 width=12) (actual time=11027.808..183839.289 rows=5 loops=1) Filter: ((2 = id_status) AND (date_from <= LOCALTIMESTAMP) AND (date_to >= LOCALTIMESTAMP) AND (SubPlan 1)) Rows Removed by Filter: 4685618 Buffers: shared hit=15414533 read=564480 written=504 SubPlan 1 -> Index Only Scan using ix_ngx_tag_content on ngx_tag_content "Extent3" (cost=0.43..8.46 rows=1 width=0) (actual time=0.003..0.003 rows=0 loops=4484963) Index Cond: (("TagId" = 337139) AND ("ContentId" = "Extent1".id)) Heap Fetches: 5 Buffers: shared hit=13454890 read=4 -> Index Scan using ng_path_content_id_content_idx on ng_path_content "Extent2" (cost=0.43..0.53 rows=1 width=4) (actual time=1.956..1.958 rows=1 loops=5) Index Cond: (id_content = "Extent1".id) Filter: (id_path = ANY ('{27495,27554,27555}'::integer[])) Buffers: shared hit=15 read=5 Planning: Buffers: shared hit=474 read=76 Planning Time: 113.080 ms Execution Time: 183849.283 ms Can someone help me understand what's going on? -- Paulo Silva <paulo...@gmail.com>