On Wed, 2008-11-05 at 13:12 +0200, Віталій Тимчишин wrote: > For a long time already I can see very poor OR performance in > postgres. > If one have query like "select something from table where condition1 > or condition2" it may take ages to execute while > "select something from table where condition1" and "select something > from table where condition2" are executed very fast and > "select something from table where condition1 and not condition2 union > all select something from table where condition2" gives required > results fast >
What version are you using?
Server version 8.3.3
Have you run "VACUUM ANALYZE"?
I have autovacuum, but for this example I did vacuum analyze of the whole DB. The real-life query (autogenerated) looks like the next: select t0.id as pk1,t1.id as pk2 ,t0.run_id as f1_run_id,t1.run_id as f2_run_id from tmpv_unproc_null_production_company_dup_cons_company as t0, (select * from production.company where run_id in (select id from production.run where name='test')) as t1 where t0.name = t1.name or (t0.name,t1.name) in (select s1.name, s2.name from atom_match inner join atoms_string s1 on atom_match.atom1_id = s1.id inner join atoms_string s2 on atom_match.atom2_id = s2.id where s1.atom_type_id = -1 and match_function_id = 2)
with tmpv_unproc_null_production_company_dup_cons_company:
create temporary view tmpv_unproc_null_production_company_dup_cons_company as select * from production.company where 1=1 and status='unprocessed' and run_id in (select id from production.run where name='test')
Next, do:
EXPLAIN ANALYZE select something from table where condition1 or condition2;
without analyze is in OR-plan.txt Also plans for only condition1, only condition2 and union is attached
