View with an outer join - is there any way to optimise this?

From: Rich Doughty <rich(at)opusvl(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: View with an outer join - is there any way to optimise this?
Date: 2005-12-12 16:31:10
Message-ID: 439DA5CE.8000704@opusvl.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-general


I have a view vw_tokens defined as

CREATE VIEW tokens.vw_tokens AS SELECT
-- too many columns to mention
FROM
tokens.ta_tokens t LEFT JOIN
tokens.ta_tokenhist i ON t.token_id = i.token_id AND
i.status = 'issued' LEFT JOIN
tokens.ta_tokenhist s ON t.token_id = s.token_id AND
s.status = 'sold' LEFT JOIN
tokens.ta_tokenhist r ON t.token_id = r.token_id AND
r.status = 'redeemed'
;

the ta_tokens table contains approx 4 million records, and ta_tokenhist
approx 10 millions. queries against the view itself on the primary key
execute with no issues at all.

I cannot however perform a meaningful join against this view. when i
execute

SELECT *
FROM
tokens.ta_tokenhist h INNER JOIN
tokens.vw_tokens t ON h.token_id = t.token_id
WHERE
h.sarreport_id = 9
;

PG forms the full output of the view. the query plan is

Hash Join (cost=1638048.47..3032073.73 rows=1 width=702)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Hash Left Join (cost=1638042.45..3011803.15 rows=4052907 width=470)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Hash Left Join (cost=1114741.93..2011923.86 rows=4052907 width=322)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Hash Left Join (cost=559931.55..1093783.71 rows=4052907 width=174)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Seq Scan on ta_tokens t (cost=0.00..73250.07 rows=4052907 width=26)
-> Hash (cost=459239.41..459239.41 rows=4114456 width=152)
-> Seq Scan on ta_tokenhist i (cost=0.00..459239.41 rows=4114456 width=152)
Filter: ((status)::text = 'issued'::text)
-> Hash (cost=459239.41..459239.41 rows=3905186 width=152)
-> Seq Scan on ta_tokenhist s (cost=0.00..459239.41 rows=3905186 width=152)
Filter: ((status)::text = 'sold'::text)
-> Hash (cost=459239.41..459239.41 rows=2617645 width=152)
-> Seq Scan on ta_tokenhist r (cost=0.00..459239.41 rows=2617645 width=152)
Filter: ((status)::text = 'redeemed'::text)
-> Hash (cost=6.01..6.01 rows=1 width=236)
-> Index Scan using fkx_tokenhist__sarreports on ta_tokenhist h (cost=0.00..6.01 rows=1 width=236)
Index Cond: ((sarreport_id)::integer = 9)

I have also tried explicitly querying token_id in the view, hoping
to force a nested loop:

EXPLAIN
SELECT *
FROM
tokens.vw_tokens__user
WHERE
token_id IN (SELECT token_id FROM tokens.ta_tokenhist WHERE sarreport_id = 9);

QUERY PLAN
----------------------------------------------------------------------------------------------------------
Hash IN Join (cost=1638048.47..3032073.73 rows=1 width=470)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Hash Left Join (cost=1638042.45..3011803.15 rows=4052907 width=470)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Hash Left Join (cost=1114741.93..2011923.86 rows=4052907 width=322)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Hash Left Join (cost=559931.55..1093783.71 rows=4052907 width=174)
Hash Cond: (("outer".token_id)::integer = ("inner".token_id)::integer)
-> Seq Scan on ta_tokens t (cost=0.00..73250.07 rows=4052907 width=26)
-> Hash (cost=459239.41..459239.41 rows=4114456 width=152)
-> Seq Scan on ta_tokenhist i (cost=0.00..459239.41 rows=4114456 width=152)
Filter: ((status)::text = 'issued'::text)
-> Hash (cost=459239.41..459239.41 rows=3905186 width=152)
-> Seq Scan on ta_tokenhist s (cost=0.00..459239.41 rows=3905186 width=152)
Filter: ((status)::text = 'sold'::text)
-> Hash (cost=459239.41..459239.41 rows=2617645 width=152)
-> Seq Scan on ta_tokenhist r (cost=0.00..459239.41 rows=2617645 width=152)
Filter: ((status)::text = 'redeemed'::text)
-> Hash (cost=6.01..6.01 rows=1 width=4)
-> Index Scan using fkx_tokenhist__sarreports on ta_tokenhist (cost=0.00..6.01 rows=1 width=4)
Index Cond: ((sarreport_id)::integer = 9)

Setting enable_mergejoin and enable_hashjoin to off results in a nested
but still forms the view output.

I can achieve the results i need be eliminating the view and writing
the query manually but for various reasons i'd prefer to query a
view.

Any advice is greatly appreciated. i'm starting to wonder if the using
a view in this instance is futile.

Many thanks

--

- Rich Doughty

Responses

Browse pgsql-general by date

  From Date Subject
Next Message John McCawley 2005-12-12 16:42:35 Re: View with an outer join - is there any way to optimise
Previous Message Frank van Vugt 2005-12-12 16:16:01 Re: PL/pgSQL : notion of deferred execution