任何想法如何加快这个查询?
输入
EXPLAIN SELECT entityid FROM entity e
LEFT JOIN level1entity l1 ON l1.level1id = e.level1_level1id
LEFT JOIN level2entity l2 ON l2.level2id = l1.level2_level2id
WHERE
l2.userid = 'a987c246-65e5-48f6-9d2d-a7bcb6284c8f'
AND
(entityid NOT IN
(1377776,1377792,1377793,1377794,1377795,1377796... 50000 ids)
)
产量
Nested Loop (cost=0.00..1452373.79 rows=3865 width=8)
-> Nested Loop (cost=0.00..8.58 rows=1 width=8)
Join Filter: (l1.level2_level2id = l2.level2id)
-> Seq Scan on level2entity l2 (cost=0.00..3.17 rows=1 width=8)
Filter: ((userid)::text = 'a987c246-65e5-48f6-9d2d-a7bcb6284c8f'::text)
-> Seq Scan on level1entity l1 (cost=0.00..4.07 rows=107 width=16)
-> Index Scan using fk_fk18edb1cfb2a41235_idx on entity e (cost=0.00..1452086.09 rows=22329 width=16)
Index Cond: (level1_level1id = l1.level1id)
好的这里是一个简化版本,连接不是瓶颈
SELECT enitityid FROM
(SELECT enitityid FROM enitity e LIMIT 5000) a
WHERE
(enitityid NOT IN
(1377776,1377792,1377793,1377794,1377795, ... 50000 ids)
)
问题是要找到没有任何这些ID的内容
说明
Subquery Scan on a (cost=0.00..312667.76 rows=1 width=8)
Filter: (e.entityid <> ALL ('{1377776,1377792,1377793,1377794, ... 50000 ids}'::bigint[]))
-> Limit (cost=0.00..111.51 rows=5000 width=8)
-> Seq Scan on entity e (cost=0.00..29015.26 rows=1301026 width=8)
一个巨大的IN
列表是非常低效的。 PostgreSQL理想情况下应该识别它并将其转换为一个反连接的关系,但此时查询规划器不知道如何做到这一点,并且识别这种情况所需的规划时间将花费每个查询明智地使用NOT IN
,所以它必须是一个非常低成本的检查。见this earlier much more detailed answer on the topic。
正如大卫·阿尔德里奇所写的那样,最好通过将其变成反连接来解决。我把它写成VALUES
列表中的连接只是因为PostgreSQL非常快速地将VALUES
列表解析成关系,但效果是一样的:
SELECT entityid
FROM entity e
LEFT JOIN level1entity l1 ON l.level1id = e.level1_level1id
LEFT JOIN level2entity l2 ON l2.level2id = l1.level2_level2id
LEFT OUTER JOIN (
VALUES
(1377776),(1377792),(1377793),(1377794),(1377795),(1377796)
) ex(ex_entityid) ON (entityid = ex_entityid)
WHERE l2.userid = 'a987c246-65e5-48f6-9d2d-a7bcb6284c8f'
AND ex_entityid IS NULL;
对于一组足够大的值,你甚至可以更好地创建一个临时表,qazxs将值插入其中,在其上创建一个COPY
,然后加入它。
探索的可能性更多:
PRIMARY KEY
好的我的解决方案是
如中所述
with exclude_list as (
select unnest(string_to_array('1377776,1377792,1377793,1377794,1377795, ...',','))::integer entity_id)
select entity_id
from entity left join exclude_list on entity.entity_id = exclude_list.entity_id
where exclude_list.entity_id is null;
因为你需要level2entity记录,因为你的where子句检查特定的用户ID“l2.userid =”你应该将你的“LEFT JOIN level2entity”变成“INNER JOIN level2entity”
http://blog.hagander.net/archives/66-Speeding-up-NOT-IN.html
希望能够过滤掉你的实体,这样你的NOT IN就可以减少工作量。