From: Ksenia Marasanova <ksenia.marasanova@gmail.com>
To: pgsql-performance@postgresql.org
Subject: LEFT JOIN optimization
Date: Sun, 11 Sep 2005 20:12:58 +0300
Message-ID: <130df19305091110125a2d174f@mail.gmail.com> (raw)
Hi list,
I don't have much experience with Postgres optimization, somehow I was
happily avoiding anything more difficult than simple select statement,
and it was working all right.
Now LEFT JOIN must be used, and I am not happy with the performance:
It takes about 5 seconds to run very simple LEFT JOIN query on a table
"user_" with ~ 13.000 records left joined to table "church" with ~ 300
records on Powerbook PPC 1.67 GHz with 1.5 GB ram.
Is it normal?
Some details:
test=# explain select * from user_ left join church on user_.church_id
= church.id;
QUERY PLAN
---------------------------------------------------------------------
Hash Left Join (cost=6.44..7626.69 rows=12763 width=325)
Hash Cond: ("outer".church_id = "inner".id)
-> Seq Scan on user_ (cost=0.00..7430.63 rows=12763 width=245)
-> Hash (cost=5.75..5.75 rows=275 width=80)
-> Seq Scan on church (cost=0.00..5.75 rows=275 width=80)
(5 rows)
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To: pgsql-performance@postgresql.org
Cc: ksenia.marasanova@gmail.com
Subject: Re: LEFT JOIN optimization
In-Reply-To: <130df19305091110125a2d174f@mail.gmail.com>
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