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
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