Postgresql 采用嵌套循环而不是哈希联接的查询
下面的查询是嵌套循环，运行21分钟，禁用嵌套循环后，它将在<1分钟内工作。表的统计信息是最新的，并且在表上运行vacuum，这可以解释为什么postgres采用嵌套循环而不是高效的哈希连接 另外，要禁用嵌套循环，最好将enable_nestloop设置为off还是增加随机页面成本？我认为将nestloop设置为off会阻止计划使用nestloop，如果它在某些地方是有效的。有什么更好的选择，请告知Postgresql 采用嵌套循环而不是哈希联接的查询,postgresql,Postgresql,下面的查询是嵌套循环，运行21分钟，禁用嵌套循环后，它将在
SELECT DISTINCT ON (three.quebec_delta)
last_value(three.reviewed_by_nm) OVER wnd AS reviewed_by_nm,
last_value(three.reviewer_specialty_nm) OVER wnd AS reviewer_specialty_nm,
last_value(three.kilo) OVER wnd AS kilo,
last_value(three.review_reason_dscr) OVER wnd AS review_reason_dscr,
last_value(three.review_notes) OVER wnd AS review_notes,
last_value(three.seven_uniform_charlie) OVER wnd AS seven_uniform_charlie,
last_value(three.di_audit_source_system_cd) OVER wnd AS di_audit_source_system_cd,
last_value(three.di_audit_update_dtm) OVER wnd AS di_audit_update_dtm,
three.quebec_delta
FROM
ods_authorization.quebec_foxtrot seven_uniform_foxtrot
JOIN ods_authorization.golf echo ON seven_uniform_foxtrot.four = echo.oscar
JOIN ods_authorization.papa three ON echo.five = three.quebec_delta
AND three.xray = '0'::bpchar
WHERE
seven_uniform_foxtrot.two_india >= (zulu () - '2 years'::interval)
AND lima (three.kilo, 'ADVISOR'::character varying)::text = 'ADVISOR'::text
WINDOW wnd AS (PARTITION BY three.quebec_delta ORDER BY three.seven_uniform_charlie DESC ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
Unique (cost=550047.63..550257.15 rows=5238 width=281) (actual time=1295000.966..1296128.356 rows=319863 loops=1)
-> WindowAgg (cost=550047.63..550244.06 rows=5238 width=281) (actual time=1295000.964..1296013.046 rows=461635 loops=1)
-> Sort (cost=550047.63..550060.73 rows=5238 width=326) (actual time=1295000.929..1295089.796 rows=461635 loops=1)
Sort Key: three.quebec_delta, three.seven_uniform_charlie DESC
Sort Method: quicksort Memory: 197021kB
-> Nested Loop (cost=1001.12..549724.06 rows=5238 width=326) (actual time=8.274..1292470.826 rows=461635 loops=1)
-> Gather (cost=1000.56..527782.84 rows=24896 width=391) (actual time=4.287..12701.687 rows=3484699 loops=1)
Workers Planned: 2
Workers Launched: 2
-> Nested Loop (cost=0.56..524293.24 rows=10373 width=391) (actual time=3.492..400998.923 rows=1161566 loops=3)
-> Parallel Seq Scan on papa three (cost=0.00..436912.84 rows=10373 width=326) (actual time=1.554..2455.626 rows=1161566 loops=3)
Filter: ((xray = 'november'::bpchar) AND ((lima_sierra(kilo, 'two_zulu'::character varying))::text = 'two_zulu'::text))
Rows Removed by Filter: 501723
-> Index Scan using five_tango on golf echo (cost=0.56..8.42 rows=1 width=130) (actual time=0.342..0.342 rows=1 loops=3484699)
Index Cond: (five_hotel = three.quebec_delta)
-> Index Scan using lima_alpha on quebec_foxtrot seven_uniform_foxtrot (cost=0.56..0.88 rows=1 width=65) (actual time=0.366..0.366 rows=0 loops=3484699)
Index Cond: (four = echo.oscar)
Filter: (two_india >= (zulu() - 'two_two'::interval))
Rows Removed by Filter: 1
Planning time: 0.777 ms
Execution time: 1296183.259 ms
Unique (cost=5933437.24..5933646.68 rows=5236 width=281) (actual time=19898.050..20993.124 rows=319980 loops=1)
-> WindowAgg (cost=5933437.24..5933633.59 rows=5236 width=281) (actual time=19898.049..20879.655 rows=461769 loops=1)
-> Sort (cost=5933437.24..5933450.33 rows=5236 width=326) (actual time=19898.022..19978.839 rows=461769 loops=1)
Sort Key: three.quebec_delta, three.seven_uniform_charlie DESC
Sort Method: quicksort Memory: 197056kB
-> Hash Join (cost=1947451.87..5933113.80 rows=5236 width=326) (actual time=11616.323..17931.146 rows=461769 loops=1)
Hash Cond: (echo.oscar = seven_uniform_foxtrot.four)
-> Gather (cost=438059.74..4423656.32 rows=24897 width=391) (actual time=1909.685..7291.289 rows=3484833 loops=1)
Workers Planned: 2
Workers Launched: 2
-> Parallel Hash Join (cost=437059.74..4420166.62 rows=10374 width=391) (actual time=1904.546..7385.948 rows=1161611 loops=3)
Hash Cond: (echo.five = three.quebec_delta)
-> Parallel Seq Scan on golf echo (cost=0.00..3921922.09 rows=8152209 width=130) (actual time=0.003..1756.576 rows=6531668 loops=3)
-> Parallel Hash (cost=436930.07..436930.07 rows=10374 width=326) (actual time=1904.354..1904.354 rows=1161611 loops=3)
Buckets: 4194304 (originally 32768) Batches: 1 (originally 1) Memory Usage: 1135200kB
-> Parallel Seq Scan on papa three (cost=0.00..436930.07 rows=10374 width=326) (actual time=0.009..963.728 rows=1161611 loops=3)
Filter: ((xray = 'november'::bpchar) AND ((lima(kilo, 'two_zulu'::character varying))::text = 'two_zulu'::text))
Rows Removed by Filter: 502246
-> Hash (cost=1476106.74..1476106.74 rows=2662831 width=65) (actual time=9692.517..9692.517 rows=2685656 loops=1)
Buckets: 4194304 Batches: 1 Memory Usage: 287171kB
-> Seq Scan on quebec_foxtrot seven_uniform_foxtrot (cost=0.00..1476106.74 rows=2662831 width=65) (actual time=0.026..8791.556 rows=2685656 loops=1)
Filter: (two_india >= (zulu() - 'two_two'::interval))
Rows Removed by Filter: 9984069
Planning time: 0.742 ms
Execution time: 21218.770 ms
在
papa上尝试索引（lima_sierra（kilo，'two_zulu'：字符变化））分析表。有了该索引，PostgreSQL将收集表达式的统计信息，这将改进估计，从而不会得到嵌套的循环联接。尝试在papa（lima_sierra（kilo，'two_zulu'：：character variable））上建立索引。
和分析表。有了该索引，PostgreSQL将收集表达式的统计信息，这将改进估计值，这样就不会得到嵌套的循环联接。如果您只是将COALESCE（r\u cd，'ADVISOR'）='ADVISOR'
替换为
(r_cd = 'ADVISOR' or r_cd IS NULL)
这可能会使用当前的表统计信息来改进估计值，使之足以更改计划。如果您只是将COALESCE（r\u cd，'ADVISOR'）='ADVISOR'
替换为
(r_cd = 'ADVISOR' or r_cd IS NULL)
这可能会使用当前的表统计信息来改进估计值，从而足以更改计划。您能告诉我们lima_sierra函数的实际内容吗？它的-Filter:（（d_flg='0'：：bpchar）和（（COALESCE（r_cd，'ADVISOR'：：character variable））：：text='ADVISOR'：：text））。用于屏蔽原始查询的标识。您能告诉我们函数lima_sierra实际上是什么吗？它的-Filter:（（d_flg='0'：：bpchar）和（（COALESCE（r_cd，'ADVISOR'：：character variabling））：：text='ADVISOR'：：text））。用于掩盖原始查询的身份。谢谢，这也起作用。谢谢，这也起作用。谢谢，这起作用了。谢谢，这起作用了。谢谢，这起作用了。