OBS: If you already have lots of indexes in your tables it may be a good time for you re-think your strategy because it´s ot working.
Tips:
1 - create indexes for the tables with the fields that you will use in the query if it is your most important query. If you have others querys that are used please post those here and we can help you to desing a better plan.
2 - You cold give us the configuration os the hardware and the posgresql configuration file and we can see what is going on.
Regards
On Thu, Nov 6, 2008 at 8:46 AM, Віталій Тимчишин <tivv00@xxxxxxxxx> wrote:
My main message is that I can see this in many queries and many times. But OK, I can present exact example.
2008/11/5 Jeff Davis <pgsql@xxxxxxxxxxx>
On Wed, 2008-11-05 at 13:12 +0200, Віталій Тимчишин wrote:What version are you using?
> 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
>
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
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