From: Evgeniy Shishkin <itparanoia@gmail.com>
To: pgsql-performance@postgresql.org list <pgsql-performance@postgresql.org>
Subject: two table join with order by on both tables attributes
Date: Fri, 8 Aug 2014 02:21:51 +0300
Message-ID: <8501437C-8756-47B8-8691-CFD97717ACBB@gmail.com> (raw)
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Hello,
suppose you have two very simple tables with fk dependency, by which we join them
and another attribute for sorting
like this
select * from users join notifications on users.id=notifications.user_id ORDER BY users.priority desc ,notifications.priority desc limit 10;
Very typical web query.
No matter which composite indexes i try, postgresql can not make efficient nested loop plan using indexes.
It chooses all sorts of seq scans and hash joins or merge join and always a sort node and then a limit 10.
Neither plan provides acceptable performance. And tables tend to grow =\
Can anybody suggest something or explain this behavior?
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To: pgsql-performance@postgresql.org
Cc: itparanoia@gmail.com
Subject: Re: two table join with order by on both tables attributes
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