From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: tim3sp@gmail.com
Subject: BUG #17862: Overall query cost ignores window function
Date: Wed, 22 Mar 2023 17:42:03 +0000
Message-ID: <17862-1ab8f74b0f7b0611@postgresql.org> (raw)
The following bug has been logged on the website:
Bug reference: 17862
Logged by: Tim Palmer
Email address: tim3sp@gmail.com
PostgreSQL version: 15.2
Operating system: Debian
Description:
This query needs to read all of large_table to count the number of rows,
despite the LIMIT clause:
SELECT large_table.*, count(*) OVER ()
FROM generate_series(1, 1000000000000) large_table
LIMIT 10
I would have expected a query plan something like this, with a large overall
cost:
Limit (cost=0.00..22500000000.00 rows=10 width=16)
-> WindowAgg (cost=0.00..22500000000.00 rows=1000000000000 width=16)
-> Function Scan on generate_series large_table
(cost=0.00..10000000000.00 rows=1000000000000 width=8)
But I actually get this query plan, with a cost of 0.23:
Limit (cost=0.00..0.23 rows=10 width=16)
-> WindowAgg (cost=0.00..22500000000.00 rows=1000000000000 width=16)
-> Function Scan on generate_series large_table
(cost=0.00..10000000000.00 rows=1000000000000 width=8)
I believe this (on a more complicated query) is affecting the plan chosen by
the optimizer.
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To: pgsql-bugs@postgresql.org
Cc: noreply@postgresql.org, pgsql-bugs@lists.postgresql.org, tim3sp@gmail.com
Subject: Re: BUG #17862: Overall query cost ignores window function
In-Reply-To: <17862-1ab8f74b0f7b0611@postgresql.org>
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