过去几周我一直试图诊断一个问题。我们的生产数据库需要很长时间（84秒）来运行在QA DB（120ms）上运行速度非常快的查询。
PostgreSQL 9.3.16 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4, 64-bit PostgreSQL 9.6.4 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4, 64-bit EXPLAIN (ANALYZE, BUFFERS)表示两个dbs的查询计划完全不同，但我无法理解差异你能做些什么来指引我朝着正确的方向前进，我真的很感激 谢谢
生产查询计划：
Limit (cost=5411.63..5411.63 rows=1 width=47) (actual time=84719.786..84719.788 rows=10 loops=1)
Buffers: shared hit=109988
-> Sort (cost=5411.63..5411.63 rows=1 width=47) (actual time=84719.785..84719.787 rows=10 loops=1)
Sort Key: events.updated_at
Sort Method: top-N heapsort Memory: 25kB
Buffers: shared hit=109988
-> Nested Loop Left Join (cost=5371.22..5411.63 rows=1 width=47) (actual time=273.194..84652.985 rows=25846 loops=1)
Join Filter: (events.id = filters_2.target_id)
Rows Removed by Join Filter: 134062366
Filter: ((filters_2.target_id IS NULL) OR (filters_1.target_id IS NOT NULL))
Rows Removed by Filter: 60
Buffers: shared hit=109988
-> Nested Loop Left Join (cost=2468.49..2481.16 rows=1 width=51) (actual time=119.443..15665.354 rows=25906 loops=1)
Join Filter: (events.id = filters_1.target_id)
Rows Removed by Join Filter: 29713058
Buffers: shared hit=108373
-> Nested Loop (cost=1241.39..1253.61 rows=1 width=47) (actual time=94.514..692.546 rows=25906 loops=1)
Buffers: shared hit=107956
-> Merge Anti Join (cost=1241.31..1241.34 rows=3 width=47) (actual time=94.497..151.266 rows=26171 loops=1)
Merge Cond: (events.id = filters.target_id)
Buffers: shared hit=2439
-> Sort (cost=14.16..14.17 rows=3 width=47) (actual time=64.147..84.460 rows=26171 loops=1)
Sort Key: events.id
Sort Method: quicksort Memory: 3131kB
Buffers: shared hit=2022
-> Bitmap Heap Scan on events (cost=4.18..14.16 rows=3 width=47) (actual time=3.687..46.416 rows=26171 loops=1)
Recheck Cond: (((brand_id = 218) AND (brand_id = 218)) OR ((brand_id IS NULL) AND (brand_id = 218)))
Filter: ((eventable_type)::text = ANY ('{Achievement,Blog,Kudo,Story,User}'::text[]))
Buffers: shared hit=2022
-> BitmapOr (cost=4.18..4.18 rows=5 width=0) (actual time=3.369..3.369 rows=0 loops=1)
Buffers: shared hit=96
-> Bitmap Index Scan on index_events_on_brand_id (cost=0.00..2.10 rows=5 width=0) (actual time=3.366..3.366 rows=26171 loops=1)
Index Cond: ((brand_id = 218) AND (brand_id = 218))
Buffers: shared hit=96
-> Bitmap Index Scan on index_events_on_brand_id (cost=0.00..2.09 rows=1 width=0) (actual time=0.001..0.001 rows=0 loops=1)
Index Cond: ((brand_id IS NULL) AND (brand_id = 218))
-> Sort (cost=1227.15..1227.16 rows=19 width=4) (actual time=30.345..30.345 rows=0 loops=1)
Sort Key: filters.target_id
Sort Method: quicksort Memory: 25kB
Buffers: shared hit=417
-> HashAggregate (cost=1226.95..1227.01 rows=19 width=4) (actual time=30.336..30.336 rows=0 loops=1)
Buffers: shared hit=417
-> Bitmap Heap Scan on filters (cost=381.47..1226.89 rows=127 width=4) (actual time=30.334..30.334 rows=0 loops=1)
Recheck Cond: (((constraint_id = 218) OR ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148)) OR ((constraint_type)::text = 'Country'::text)) AND ((target_type)::text = 'Event'::text))
Filter: ((NOT visible) AND ((((constraint_type)::text = 'Brand'::text) AND (constraint_id = 218)) OR (((constraint_type)::text = 'Team'::text) AND ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148))) OR (((constraint_type)::text = 'Country'::text) AND (constraint_id IS NULL))))
Rows Removed by Filter: 1147
Buffers: shared hit=417
-> BitmapAnd (cost=381.47..381.47 rows=634 width=0) (actual time=5.591..5.591 rows=0 loops=1)
Buffers: shared hit=149
-> BitmapOr (cost=32.60..32.60 rows=2733 width=0) (actual time=0.464..0.464 rows=0 loops=1)
Buffers: shared hit=24
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.16 rows=53 width=0) (actual time=0.010..0.010 rows=0 loops=1)
Index Cond: (constraint_id = 218)
Buffers: shared hit=3
-> BitmapOr (cost=28.29..28.29 rows=2680 width=0) (actual time=0.384..0.384 rows=0 loops=1)
Buffers: shared hit=18
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.16 rows=53 width=0) (actual time=0.005..0.005 rows=0 loops=1)
Index Cond: (constraint_id = 5229)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.16 rows=53 width=0) (actual time=0.004..0.004 rows=0 loops=1)
Index Cond: (constraint_id = 5183)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..23.95 rows=2575 width=0) (actual time=0.373..0.373 rows=2979 loops=1)
Index Cond: (constraint_id = 5148)
Buffers: shared hit=12
-> Bitmap Index Scan on index_filters_on_constraint_type (cost=0.00..2.09 rows=1 width=0) (actual time=0.022..0.022 rows=0 loops=1)
Index Cond: ((constraint_type)::text = 'Country'::text)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_target_type (cost=0.00..348.81 rows=35153 width=0) (actual time=5.088..5.088 rows=35092 loops=1)
Index Cond: ((target_type)::text = 'Event'::text)
Buffers: shared hit=125
-> Index Scan using users_pkey on users (cost=0.08..4.09 rows=1 width=6) (actual time=0.016..0.018 rows=1 loops=26171)
Index Cond: (id = events.user_id)
Filter: ((active AND visible) OR ((events.eventable_type)::text = 'Blog'::text))
Rows Removed by Filter: 0
Buffers: shared hit=105517
-> HashAggregate (cost=1227.10..1227.24 rows=47 width=4) (actual time=0.001..0.309 rows=1147 loops=25906)
Buffers: shared hit=417
-> Bitmap Heap Scan on filters filters_1 (cost=381.53..1226.94 rows=311 width=4) (actual time=5.647..6.835 rows=1147 loops=1)
Recheck Cond: (((constraint_id = 218) OR ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148)) OR ((constraint_type)::text = 'Country'::text)) AND ((target_type)::text = 'Event'::text))
Filter: (visible AND ((((constraint_type)::text = 'Brand'::text) AND (constraint_id = 218)) OR (((constraint_type)::text = 'Team'::text) AND ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148))) OR (((constraint_type)::text = 'Country'::text) AND (constraint_id IS NULL))))
Buffers: shared hit=417
-> BitmapAnd (cost=381.53..381.53 rows=634 width=0) (actual time=5.595..5.595 rows=0 loops=1)
Buffers: shared hit=149
-> BitmapOr (cost=32.65..32.65 rows=2733 width=0) (actual time=0.449..0.449 rows=0 loops=1)
Buffers: shared hit=24
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.16 rows=53 width=0) (actual time=0.007..0.007 rows=0 loops=1)
Index Cond: (constraint_id = 218)
Buffers: shared hit=3
-> BitmapOr (cost=28.32..28.32 rows=2680 width=0) (actual time=0.378..0.378 rows=0 loops=1)
Buffers: shared hit=18
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.16 rows=53 width=0) (actual time=0.005..0.005 rows=0 loops=1)
Index Cond: (constraint_id = 5229)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.16 rows=53 width=0) (actual time=0.005..0.005 rows=0 loops=1)
Index Cond: (constraint_id = 5183)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..23.95 rows=2575 width=0) (actual time=0.366..0.366 rows=2979 loops=1)
Index Cond: (constraint_id = 5148)
Buffers: shared hit=12
-> Bitmap Index Scan on index_filters_on_constraint_type (cost=0.00..2.09 rows=1 width=0) (actual time=0.014..0.014 rows=0 loops=1)
Index Cond: ((constraint_type)::text = 'Country'::text)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_target_type (cost=0.00..348.81 rows=35153 width=0) (actual time=5.110..5.110 rows=35092 loops=1)
Index Cond: ((target_type)::text = 'Event'::text)
Buffers: shared hit=125
-> HashAggregate (cost=2902.73..2911.49 rows=2920 width=4) (actual time=0.006..1.438 rows=5175 loops=25906)
Buffers: shared hit=1615
-> Bitmap Heap Scan on filters filters_2 (cost=349.80..2892.87 rows=19720 width=4) (actual time=19.215..124.613 rows=34923 loops=1)
Recheck Cond: ((target_type)::text = 'Event'::text)
Filter: (visible AND ((((constraint_type)::text = 'Brand'::text) AND (constraint_id <> 218)) OR (((constraint_type)::text = 'Team'::text) AND ((constraint_id <> 5229) OR (constraint_id <> 5183) OR (constraint_id <> 5148))) OR (((constraint_type)::text = 'Country'::text) AND (constraint_id IS NOT NULL))))
Buffers: shared hit=1615
-> Bitmap Index Scan on index_filters_on_target_type (cost=0.00..348.81 rows=35153 width=0) (actual time=18.952..18.952 rows=35092 loops=1)
Index Cond: ((target_type)::text = 'Event'::text)
Buffers: shared hit=125
Total runtime: 84720.000 ms
(116 rows)
质量检查查询计划：
Limit (cost=5474.52..5474.52 rows=10 width=47) (actual time=117.227..117.229 rows=10 loops=1)
Buffers: shared hit=97438
-> Sort (cost=5474.52..5474.56 rows=97 width=47) (actual time=117.227..117.227 rows=10 loops=1)
Sort Key: events.updated_at DESC
Sort Method: top-N heapsort Memory: 25kB
Buffers: shared hit=97438
-> Hash Left Join (cost=4013.62..5474.10 rows=97 width=47) (actual time=29.635..110.750 rows=23404 loops=1)
Hash Cond: (events.id = filters_2.target_id)
Filter: ((filters_2.target_id IS NULL) OR (filters_1.target_id IS NOT NULL))
Rows Removed by Filter: 60
Buffers: shared hit=97438
-> Hash Left Join (cost=2023.52..3483.92 rows=97 width=51) (actual time=8.641..83.892 rows=23464 loops=1)
Hash Cond: (events.id = filters_1.target_id)
Buffers: shared hit=96393
-> Hash Anti Join (cost=1012.67..2472.99 rows=97 width=47) (actual time=4.906..75.057 rows=23464 loops=1)
Hash Cond: (events.id = filters.target_id)
Buffers: shared hit=96119
-> Nested Loop (cost=5.00..1464.98 rows=97 width=47) (actual time=1.750..66.678 rows=23464 loops=1)
Buffers: shared hit=95845
-> Bitmap Heap Scan on events (cost=4.92..667.30 rows=214 width=47) (actual time=1.738..9.563 rows=23720 loops=1)
Recheck Cond: (((brand_id = 218) AND (brand_id = 218)) OR ((brand_id IS NULL) AND (brand_id = 218)))
Filter: ((eventable_type)::text = ANY ('{Achievement,Blog,Kudo,Story,User}'::text[]))
Heap Blocks: exact=801
Buffers: shared hit=869
-> BitmapOr (cost=4.92..4.92 rows=361 width=0) (actual time=1.630..1.630 rows=0 loops=1)
Buffers: shared hit=68
-> Bitmap Index Scan on index_events_on_brand_id (cost=0.00..2.81 rows=361 width=0) (actual time=1.629..1.629 rows=23720 loops=1)
Index Cond: ((brand_id = 218) AND (brand_id = 218))
Buffers: shared hit=68
-> Bitmap Index Scan on index_events_on_brand_id (cost=0.00..2.09 rows=1 width=0) (actual time=0.001..0.001 rows=0 loops=1)
Index Cond: ((brand_id IS NULL) AND (brand_id = 218))
-> Index Scan using users_pkey on users (cost=0.08..3.72 rows=1 width=6) (actual time=0.002..0.002 rows=1 loops=23720)
Index Cond: (id = events.user_id)
Filter: ((active AND visible) OR ((events.eventable_type)::text = 'Blog'::text))
Rows Removed by Filter: 0
Buffers: shared hit=94976
-> Hash (cost=1007.22..1007.22 rows=128 width=4) (actual time=3.145..3.145 rows=0 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8kB
Buffers: shared hit=274
-> Unique (cost=1006.71..1006.84 rows=128 width=4) (actual time=3.145..3.145 rows=0 loops=1)
Buffers: shared hit=274
-> Sort (cost=1006.71..1006.77 rows=128 width=4) (actual time=3.145..3.145 rows=0 loops=1)
Sort Key: filters.target_id
Sort Method: quicksort Memory: 25kB
Buffers: shared hit=274
-> Bitmap Heap Scan on filters (cost=283.82..1005.81 rows=128 width=4) (actual time=3.137..3.137 rows=0 loops=1)
Recheck Cond: (((constraint_id = 218) OR ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148)) OR ((constraint_type)::text = 'Country'::text)) AND ((target_type)::text = 'Event'::text))
Filter: ((NOT visible) AND ((((constraint_type)::text = 'Brand'::text) AND (constraint_id = 218)) OR (((constraint_type)::text = 'Team'::text) AND ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148))) OR (((constraint_type)::text = 'Country'::text) AND (constraint_id IS NULL))))
Rows Removed by Filter: 974
Heap Blocks: exact=156
Buffers: shared hit=274
-> BitmapAnd (cost=283.82..283.82 rows=641 width=0) (actual time=2.809..2.809 rows=0 loops=1)
Buffers: shared hit=118
-> BitmapOr (cost=28.65..28.65 rows=2762 width=0) (actual time=0.237..0.237 rows=0 loops=1)
Buffers: shared hit=22
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.17 rows=56 width=0) (actual time=0.005..0.005 rows=0 loops=1)
Index Cond: (constraint_id = 218)
Buffers: shared hit=3
-> BitmapOr (cost=24.33..24.33 rows=2707 width=0) (actual time=0.189..0.189 rows=0 loops=1)
Buffers: shared hit=16
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.17 rows=56 width=0) (actual time=0.003..0.003 rows=0 loops=1)
Index Cond: (constraint_id = 5229)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.17 rows=56 width=0) (actual time=0.003..0.003 rows=0 loops=1)
Index Cond: (constraint_id = 5183)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..19.98 rows=2596 width=0) (actual time=0.183..0.183 rows=2502 loops=1)
Index Cond: (constraint_id = 5148)
Buffers: shared hit=10
-> Bitmap Index Scan on index_filters_on_constraint_type (cost=0.00..2.09 rows=1 width=0) (actual time=0.010..0.010 rows=0 loops=1)
Index Cond: ((constraint_type)::text = 'Country'::text)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_target_type (cost=0.00..255.12 rows=34021 width=0) (actual time=2.555..2.555 rows=33832 loops=1)
Index Cond: ((target_type)::text = 'Event'::text)
Buffers: shared hit=96
-> Hash (cost=1009.75..1009.75 rows=314 width=4) (actual time=3.727..3.727 rows=974 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 43kB
Buffers: shared hit=274
-> Unique (cost=1008.49..1008.81 rows=314 width=4) (actual time=3.383..3.596 rows=974 loops=1)
Buffers: shared hit=274
-> Sort (cost=1008.49..1008.65 rows=316 width=4) (actual time=3.381..3.453 rows=974 loops=1)
Sort Key: filters_1.target_id
Sort Method: quicksort Memory: 70kB
Buffers: shared hit=274
-> Bitmap Heap Scan on filters filters_1 (cost=283.88..1005.87 rows=316 width=4) (actual time=2.765..3.224 rows=974 loops=1)
Recheck Cond: (((constraint_id = 218) OR ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148)) OR ((constraint_type)::text = 'Country'::text)) AND ((target_type)::text = 'Event'::text))
Filter: (visible AND ((((constraint_type)::text = 'Brand'::text) AND (constraint_id = 218)) OR (((constraint_type)::text = 'Team'::text) AND ((constraint_id = 5229) OR (constraint_id = 5183) OR (constraint_id = 5148))) OR (((constraint_type)::text = 'Country'::text) AND (constraint_id IS NULL))))
Heap Blocks: exact=156
Buffers: shared hit=274
-> BitmapAnd (cost=283.88..283.88 rows=641 width=0) (actual time=2.744..2.744 rows=0 loops=1)
Buffers: shared hit=118
-> BitmapOr (cost=28.70..28.70 rows=2762 width=0) (actual time=0.202..0.202 rows=0 loops=1)
Buffers: shared hit=22
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.17 rows=56 width=0) (actual time=0.003..0.003 rows=0 loops=1)
Index Cond: (constraint_id = 218)
Buffers: shared hit=3
-> BitmapOr (cost=24.36..24.36 rows=2707 width=0) (actual time=0.169..0.169 rows=0 loops=1)
Buffers: shared hit=16
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.17 rows=56 width=0) (actual time=0.002..0.002 rows=0 loops=1)
Index Cond: (constraint_id = 5229)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..2.17 rows=56 width=0) (actual time=0.001..0.001 rows=0 loops=1)
Index Cond: (constraint_id = 5183)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_constraint_id (cost=0.00..19.98 rows=2596 width=0) (actual time=0.165..0.165 rows=2502 loops=1)
Index Cond: (constraint_id = 5148)
Buffers: shared hit=10
-> Bitmap Index Scan on index_filters_on_constraint_type (cost=0.00..2.09 rows=1 width=0) (actual time=0.006..0.006 rows=0 loops=1)
Index Cond: ((constraint_type)::text = 'Country'::text)
Buffers: shared hit=3
-> Bitmap Index Scan on index_filters_on_target_type (cost=0.00..255.12 rows=34021 width=0) (actual time=2.525..2.525 rows=33832 loops=1)
Index Cond: ((target_type)::text = 'Event'::text)
Buffers: shared hit=96
-> Hash (cost=1943.94..1943.94 rows=13189 width=4) (actual time=20.931..20.931 rows=4918 loops=1)
Buckets: 16384 Batches: 1 Memory Usage: 301kB
Buffers: shared hit=1045
-> HashAggregate (cost=1864.80..1904.37 rows=13189 width=4) (actual time=19.485..20.163 rows=4918 loops=1)
Group Key: filters_2.target_id
Buffers: shared hit=1045
-> Bitmap Heap Scan on filters filters_2 (cost=256.07..1855.22 rows=19167 width=4) (actual time=2.605..13.438 rows=33832 loops=1)
Recheck Cond: ((target_type)::text = 'Event'::text)
Filter: (visible AND ((((constraint_type)::text = 'Brand'::text) AND (constraint_id <> 218)) OR (((constraint_type)::text = 'Team'::text) AND ((constraint_id <> 5229) OR (constraint_id <> 5183) OR (constraint_id <> 5148))) OR (((constraint_type)::text = 'Country'::text) AND (constraint_id IS NOT NULL))))
Heap Blocks: exact=949
Buffers: shared hit=1045
-> Bitmap Index Scan on index_filters_on_target_type (cost=0.00..255.12 rows=34021 width=0) (actual time=2.482..2.482 rows=33832 loops=1)
Index Cond: ((target_type)::text = 'Event'::text)
Buffers: shared hit=96
Planning time: 1.244 ms
Execution time: 117.581 ms
(129 rows)
答案 0 :(得分：0)
TLDR：VACUUM ANALYZE是解决方案
很抱歉延迟回复。我们碰巧正在将我们的数据库迁移到另一个修复该问题的实例类型。我回到原版并尝试了这里建议的解决方案。答案是vacuum analyze。显然是Heroku autovacuums，但没有运行分析。
一个未解之谜，迁移我们的数据库将大小减半（12GB => 6GB - 行数相同）