Hi,
sorry to jump in, but looks like I have a similar pb on a 12.6 instance.
on a quite simple request,
with limit 1000 it takes 27ms, and with limit 10, it takes 145000 ms
looking at both the explain analyze plans, there is a huge difference:
with limit 1000, postgres do an optimization of the plan putting join in an efficient order. and using a hash left join
with limit 10: no optimization. so inefficient order and reading of a huge amount of data.and using a nested loop left join
stats have been updated through vacuum analyze.
If interested I can put the plans (in another thread...)
On Mon, May 10, 2021 at 11:13 PM Jonathan Chen <jonc@xxxxxxxxxxx> wrote:
Hi,
I am running Postgresql 13 as a backend for Odoo, and I believe I have
discovered a regression with the query engine.
This (simplified) query generated by the ORM takes 47.683s to complete
(the result set is empty):
SELECT "account_bank_statement_line".id
FROM "account_bank_statement_line"
LEFT JOIN "account_move" AS "account_bank_statement_line__move_id"
ON ("account_bank_statement_line"."move_id" =
"account_bank_statement_line__move_id"."id")
WHERE
(
("account_bank_statement_line"."move_id" in
(
SELECT "account_move".id
FROM "account_move"
WHERE ("account_move"."state" = 'posted')
AND ("account_move"."company_id" IS NULL OR
("account_move"."company_id" in (1)))
ORDER BY "account_move"."id"
)
)
AND ("account_bank_statement_line__move_id"."journal_id" = 29)
)
ORDER BY "account_bank_statement_line__move_id"."date" DESC,
"account_bank_statement_line"."id" DESC LIMIT 1
If I remove the "LIMIT 1" on the last line, the query completes in 0.036s.
If I remove the WHERE clause, the query completes in 0.032s.
If I run the original query on Postgresql 12.6 (on a lower spec'd
host), it completes in 0.067s.
--
Jonathan Chen <jonc@xxxxxxxxxxx>
