Hi all,
Im currently taking my first steps with db optimizations and am wondering whats happening here and if/how i can help pg choose the better plan.
Thanks, Fabian
>>>
psql (PostgreSQL) 7.2.2
perg_1097=# VACUUM ANALYZE ; VACUUM perg_1097=# EXPLAIN ANALYZE select notiz_id, obj_id, obj_typ perg_1097-# from notiz_objekt a perg_1097-# where not exists perg_1097-# ( perg_1097(# select 1 perg_1097(# from notiz_gelesen b perg_1097(# where ma_id = 2001 perg_1097(# and ma_pid = 1097 perg_1097(# and a.notiz_id = b.notiz_id perg_1097(# ) perg_1097-# ; NOTICE: QUERY PLAN:
Seq Scan on notiz_objekt a (cost=0.00..56125.80 rows=15561 width=12) (actual time=0.28..2305.52 rows=31122 loops=1)
SubPlan
-> Seq Scan on notiz_gelesen b (cost=0.00..1.79 rows=1 width=0) (actual time=0.07..0.07 rows=0 loops=31122)
Total runtime: 2334.42 msec
EXPLAIN perg_1097=# SET enable_seqscan to false; SET VARIABLE perg_1097=# EXPLAIN ANALYZE select notiz_id, obj_id, obj_typ perg_1097-# from notiz_objekt a perg_1097-# where not exists perg_1097-# ( perg_1097(# select 1 perg_1097(# from notiz_gelesen b perg_1097(# where ma_id = 2001 perg_1097(# and ma_pid = 1097 perg_1097(# and a.notiz_id = b.notiz_id perg_1097(# ) perg_1097-# ; NOTICE: QUERY PLAN:
Seq Scan on notiz_objekt a (cost=100000000.00..100111719.36 rows=15561 width=12) (actual time=0.24..538.86 rows=31122 loops=1)
SubPlan
-> Index Scan using idx_notiz_gelesen_2 on notiz_gelesen b (cost=0.00..3.57 rows=1 width=0) (actual time=0.01..0.01 rows=0 loops=31122)
Total runtime: 570.75 msec
EXPLAIN perg_1097=#
perg_1097=# \d notiz_objekt; Table "notiz_objekt" Column | Type | Modifiers ----------+---------+----------- notiz_id | integer | obj_id | integer | obj_typ | integer | Indexes: idx_notiz_objekt_1, idx_notiz_objekt_2
perg_1097=# \d notiz_gelesen;
Table "notiz_gelesen"
Column | Type | Modifiers
----------+--------------------------+----------------------------------------------------
notiz_id | integer |
ma_id | integer |
ma_pid | integer |
stamp | timestamp with time zone | default ('now'::text)::timestamp(6) with time zone
anzeigen | character varying |
Indexes: idx_notiz_gelesen_1,
idx_notiz_gelesen_2
perg_1097=#
perg_1097=# select count(*) from notiz_objekt; count ------- 31122 (1 row)
perg_1097=# select count(*) from notiz_gelesen; count ------- 45 (1 row)
perg_1097=#
idx_notiz_gelesen_1 (ma_id,ma_pid) idx_notiz_gelesen_2 (notiz_id)
---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster