From: Ilia Kantor <ilia@obnovlenie.ru>
To: pgsql-performance@postgresql.org
Subject: Planner improvement suggestion
Date: Mon, 29 Aug 2005 00:59:33 +0400
Message-ID: <auto-000558493797@umail.ru> (raw)
I have a query:
SELECT oh.id
FROM objects_hier oh
where
oh.id < 2000 (!)
and
oh.id in (
SELECT id as id FROM objects_access oa
WHERE
oa.master IN (1,2,10001)
AND
oa.id < 2000 (!)
)
The sense of the query is simple: I choose ids from objects_hier where
access has necessary masters.
The problem is: I have duplicate conditions for id here. They are marked
with '!'.
I just can't remove any of them, because planner needs to estimate both
outer and inner selects to calculate the order
Of nested loop or choose a join. If I remove one of duplicate conditions -
planner can't estimate well.
It's obvious that condition on oh.id can be put inside or outside "oh.id in
( .. )" statement with same result.
So I just suggest that the planner should take this into account and
"propagate" the condition outside or inside for planning if needed.
P.S
Is there a way to fix this particular query? Usually oh.id condition is not
like <2000, but an inner join.
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: ilia@obnovlenie.ru
Subject: Re: Planner improvement suggestion
In-Reply-To: <auto-000558493797@umail.ru>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox