same plan, add 1 condition, 1900x slower - Mailing list pgsql-performance
From | Mitch Skinner |
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Subject | same plan, add 1 condition, 1900x slower |
Date | |
Msg-id | 1131630176.29496.91.camel@enzian Whole thread Raw |
Responses |
Re: same plan, add 1 condition, 1900x slower
|
List | pgsql-performance |
This is with Postgres 8.0.3. Any advice is appreciated. I'm not sure exactly what I expect, but I was hoping that if it used the external_id_map_source_target_id index it would be faster. Mainly I was surprised that the same plan could perform so much differently with just an extra condition. I've increased the statistics target on util.external_id_map.source, but I'm fuzzy on exactly where (what columns) the planner could use more information. statgen=> explain analyze select * from subject_source; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Merge Join (cost=0.00..316.79 rows=1186 width=46) (actual time=0.136..9.808 rows=1186 loops=1) Merge Cond: ("outer".id = "inner".target_id) -> Index Scan using subject_pkey on subject norm (cost=0.00..63.36 rows=1186 width=28) (actual time=0.050..1.834 rows=1186 loops=1) -> Index Scan using external_id_map_primary_key on external_id_map eim (cost=0.00..2345747.01 rows=15560708 width=26) (actual time=0.061..2.944 rows=2175 loops=1) Total runtime: 10.745 ms (5 rows) statgen=> explain analyze select * from subject_source where source='SCH'; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Merge Join (cost=0.00..640.95 rows=1 width=46) (actual time=0.043..21074.403 rows=1186 loops=1) Merge Cond: ("outer".id = "inner".target_id) -> Index Scan using subject_pkey on subject norm (cost=0.00..63.36 rows=1186 width=28) (actual time=0.014..1.478 rows=1186 loops=1) -> Index Scan using external_id_map_primary_key on external_id_map eim (cost=0.00..2384648.78 rows=4150 width=26) (actual time=0.020..21068.508 rows=1186 loops=1) Filter: (source = 'SCH'::bpchar) Total runtime: 21075.142 ms (6 rows) statgen=> \d subject Table "public.subject" Column | Type | Modifiers ---------+---------+----------- id | bigint | not null sex | integer | parent1 | bigint | parent2 | bigint | Indexes: "subject_pkey" PRIMARY KEY, btree (id) Foreign-key constraints: "subject_parent1" FOREIGN KEY (parent1) REFERENCES subject(id) DEFERRABLE INITIALLY DEFERRED "subject_parent2" FOREIGN KEY (parent2) REFERENCES subject(id) DEFERRABLE INITIALLY DEFERRED "subject_id_map" FOREIGN KEY (id) REFERENCES util.external_id_map(target_id) DEFERRABLE INITIALLY DEFERRED statgen=> \d subject_source View "public.subject_source" Column | Type | Modifiers -----------+-----------------------+----------- id | bigint | sex | integer | parent1 | bigint | parent2 | bigint | source | character(3) | source_id | character varying(32) | View definition: SELECT norm.id, norm.sex, norm.parent1, norm.parent2, eim.source, eim.source_id FROM subject norm JOIN util.external_id_map eim ON norm.id = eim.target_id; statgen=> \d util.external_id_map Table "util.external_id_map" Column | Type | Modifiers -----------+-----------------------+----------- source_id | character varying(32) | not null source | character(3) | not null target_id | bigint | not null Indexes: "external_id_map_primary_key" PRIMARY KEY, btree (target_id) "external_id_map_source_source_id_unique" UNIQUE, btree (source, source_id) "external_id_map_source" btree (source) "external_id_map_source_target_id" btree (source, target_id) Foreign-key constraints: "external_id_map_source" FOREIGN KEY (source) REFERENCES util.source(id) Thanks in advance, Mitch
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