Postgresql 索引和 seq 扫描

Question

I'm realised that one interesting thing. I have a table with multiple column index.

CREATE INDEX transaction_idx ON transaction USING btree (period_id, day_id, value_type, indicator_id);

when I run query like :

select *
from transaction
where  period_id = '202104'
and day_id = 30
and  value_type = 1
and indicator_id = 2

DB will go seq scan.

But if I just change the day_id value to 20, then DB will go Index Scan. Go index Scan

Go Seq Scan I'm appreciate that if someone can share the root reason to me about it .

Thank you !

Answer 1

好的，我已经更新了 random_page_cost 值，查询按我的预期运行。

alter database db set random_page_cost=0.7;