Question

如何修复“项目”的顺序扫描？我已经有[league_id，buyout_amount]

的索引

"Limit  (cost=72399.08..72399.15 rows=25 width=553) (actual time=2037.893..2037.898 rows=25 loops=1)"
"  ->  Sort  (cost=72399.08..72817.16 rows=167231 width=553) (actual time=2037.891..2037.894 rows=25 loops=1)"
"        Sort Key: normalized_buyout, id"
"        Sort Method: top-N heapsort  Memory: 41kB"
"        ->  Seq Scan on items  (cost=0.00..67679.95 rows=167231 width=553) (actual time=0.764..1906.766 rows=183374 loops=1)"
"              Filter: ((buyout_amount <> 0::numeric) AND (league_id = 1))"
"Total runtime: 2037.949 ms"

这是查询

SELECT "items".* FROM "items" 
WHERE (items.league_id = '1') AND (buyout_amount <> 0) 
ORDER BY normalized_buyout ASC, items.id DESC 
LIMIT 25

当前索引（与此查询相关）

-- Index: index_items_on_buyout_amount

-- DROP INDEX index_items_on_buyout_amount;

CREATE INDEX index_items_on_buyout_amount
  ON items
  USING btree
  (buyout_amount);

-- Index: index_items_on_id

-- DROP INDEX index_items_on_id;

CREATE INDEX index_items_on_id
  ON items
  USING btree
  (id DESC);

-- Index: index_items_on_id_and_league_id

-- DROP INDEX index_items_on_id_and_league_id;

CREATE INDEX index_items_on_id_and_league_id
  ON items
  USING btree
  (id, league_id);

-- Index: index_items_on_id_and_normalized_buyout

-- DROP INDEX index_items_on_id_and_normalized_buyout;

CREATE INDEX index_items_on_id_and_normalized_buyout
  ON items
  USING btree
  (id DESC, normalized_buyout);


-- Index: index_items_on_league_id

-- DROP INDEX index_items_on_league_id;

CREATE INDEX index_items_on_league_id
  ON items
  USING btree
  (league_id);

-- Index: index_items_on_league_id_and_buyout_amount

-- DROP INDEX index_items_on_league_id_and_buyout_amount;

CREATE INDEX index_items_on_league_id_and_buyout_amount
  ON items
  USING btree
  (league_id, buyout_amount);

-- Index: index_items_on_league_id_and_id

-- DROP INDEX index_items_on_league_id_and_id;

CREATE INDEX index_items_on_league_id_and_id
  ON items
  USING btree
  (league_id, id DESC);

-- Index: index_items_on_normalized_buyout

-- DROP INDEX index_items_on_normalized_buyout;

CREATE INDEX index_items_on_normalized_buyout
  ON items
  USING btree
  (normalized_buyout);

Answer 1

我发现我的ORDER BY索引没有被使用。通过添加部分索引WHERE buyout_amount <> 0 ORDER BY normalized_buyout, id DESC，它开始使用索引。

Answer 2

对于强制类型转换，Postgres可能特别敏感/愚蠢：如果你不使用与列相同类型的常量，它（通常根据我的经验）将列强制转换为常量，从而使索引无效。

确保常量与列类型一致。

更改

WHERE items.league_id = '1' -- constant is text
AND buyout_amount <> 0 -- constant is int

要：

WHERE items.league_id = 1 -- constant is int
AND buyout_amount <> 0.0 -- constant is decimal

什么索引会修复此查询？

2 个答案: