Hi all,
If you can just help my understanding the choice of the planner.
Here is the Query:
explain analyse SELECT IRNUM FROM IR
INNER JOIN IT ON IT.ITIRNUM = ANY ('{1000, 2000}') AND IT.ITYPNUM = 'M' AND IR.IRYPNUM = IT.ITYPNUM AND IR.IRNUM = IT.ITIRNUM
WHERE IRNUM = ANY ('{1000, 2000}') and IRYPNUM = 'M'
Here is the Query plan:
| QUERY PLAN |
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| Hash Join (cost=1142.47..5581.75 rows=87 width=4) (actual time=125.000..203.000 rows=2 loops=1) |
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| Hash Cond: ("outer".itirnum = "inner".irnum) |
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| -> Seq Scan on it (cost=0.00..3093.45 rows=31646 width=9) (actual time=0.000..78.000 rows=2 loops=1) |
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| Filter: ((itirnum = ANY ('{1000,2000}'::integer[])) AND ((itypnum)::text = 'M'::text)) |
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| -> Hash (cost=1142.09..1142.09 rows=151 width=37) (actual time=125.000..125.000 rows=0 loops=1) |
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| -> Index Scan using ir_pk on ir (cost=0.00..1142.09 rows=151 width=37) (actual time=0.000..125.000 rows=2 loops=1) |
| Index Cond: ((irypnum)::text = 'M'::text) |
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| Filter: (irnum = ANY ('{1000,2000}'::integer[])) |
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| Total runtime: 203.000 ms |
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I don't understand why the planner do a Seq Scan (Seq Scan on table IT
..) instead of passing by the followin index:
ALTER TABLE IT ADD CONSTRAINT IT_IR_FK foreign key (ITYPNUM,ITIRNUM) references IR (IRYPNUM, IRNUM) ON UPDATE CASCADE;
I tried some stuff but I'm not able to change this behavior. The IT and IR table may be quite huge (from 20k to 1600k rows) so I think doing a SEQ SCAN is not a good idea.. am I wrong? Is this query plan is oki for you ?
Thanks for your help.
/David
P.S.: I'm using postgresql 8.0.3 on windows and I change those setting in my postgresql.conf :
shared_buffers = 12000 # min 16, at least max_connections*2, 8KB each
work_mem = 15000 # min 64, size in KB