Hi,
my sql is very simple,
returns one row,
where conditions are assigned to primary keys
select g.gd_index, gd.full_name
from gd g join gd_data gd on (g.id_gd = gd.id_gd)
where gd.id_gd_data = 1111 OR g.id_gd = 1111;
but generates "crazy" plan with Merge Join on big amount of rows (both tables contains 500000 rows)
because Index scans ignore conditions, conditions are processed after index sacans on Merge Join
Merge Join (cost=0.00..46399.80 rows=2 width=115) (actual time=3.881..644.409 rows=1 loops=1)
Merge Cond: (g.id_gd = gd.id_gd)
Join Filter: ((gd.id_gd_data = 1111) OR (g.id_gd = 1111))
-> Index Scan using pk_gd on gd g (cost=0.00..14117.79 rows=500001 width=40) (actual time=0.019..146.521 rows=500001 loops=1)
-> Index Scan using fki_gd on gd_data gd (cost=0.00..22282.04 rows=500001 width=99) (actual time=0.016..157.384 rows=500001 loops=1)
Total runtime: 644.460 ms
model is very simple
CREATE TABLE gd (
id_gd bigint NOT NULL,
gd_index character varying(60) NOT NULL,
notes text,
notes_exists integer NOT NULL DEFAULT 0,
CONSTRAINT pk_gd PRIMARY KEY (id_gd )
)
CREATE TABLE gd_data (
id_gd_data bigint NOT NULL,
id_gd bigint NOT NULL,
short_name character varying(120) NOT NULL,
full_name character varying(512) NOT NULL,
notes text,
notes_exists integer NOT NULL DEFAULT 0,
CONSTRAINT pk_gd_data PRIMARY KEY (id_gd_data ),
CONSTRAINT fk_gd FOREIGN KEY (id_gd)
REFERENCES gd (id_gd) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
CREATE INDEX fki_gd
ON gd_data
USING btree
(id_gd );
my configuration from (select * from pg_settings):
"server_version";"9.1.10"
"block_size";"8192"
"cpu_index_tuple_cost";"0.005"
"cpu_operator_cost";"0.0025"
"cpu_tuple_cost";"0.01"
"cursor_tuple_fraction";"0.1"
"default_statistics_target";"1000"
"enable_bitmapscan";"on"
"enable_hashagg";"on"
"enable_hashjoin";"on"
"enable_indexscan";"on"
"enable_material";"on"
"enable_mergejoin";"on"
"enable_nestloop";"on"
"enable_seqscan";"on"
"enable_sort";"on"
"enable_tidscan";"on"
"maintenance_work_mem";"262144"
"max_connections";"10"
"max_files_per_process";"1000"
"max_locks_per_transaction";"64"
"max_pred_locks_per_transaction";"64"
"max_prepared_transactions";"10"
"random_page_cost";"1.5"
"seq_page_cost";"1"
"shared_buffers";"65536"
"temp_buffers";"1024"
"work_mem";"131072"
Thank you for your help.
Kris Olszewski
|
