Re: partition queries hitting all partitions even though check key is specified

[Greg Jaman <gjaman@xxxxxxxxx>]

Check the caveats at 
http://www.postgresql.org/docs/current/static/ddl-partitioning.html

"Constraint exclusion only works when the query's WHERE clause contains constants. A parameterized query will not be optimized, since the planner cannot know which partitions the parameter value might select at run time. For the same reason, "stable" functions such as CURRENT_DATE must be avoided."

I think this applies to both your query and the CHECK statement in the table definition.

-Greg Jaman

On Wed, Sep 2, 2009 at 8:05 AM, Kevin Kempter <kevink@xxxxxxxxxxxxxxxxxxx> wrote:

On Wednesday 02 September 2009 09:02:27 Scott Marlowe wrote:
> On Wed, Sep 2, 2009 at 8:52 AM, Kevin Kempter<kevink@xxxxxxxxxxxxxxxxxxx>
wrote:
> > Hi all;
> >
> > I cant figure out why we're scanning all of our partitions.
> >
> > We setup our tables like this:
> >
> >
> > Base Table:
> >
> > CREATE TABLE url_hits (
> >    id integer NOT NULL,
> >    content_type_id integer,
> >    file_extension_id integer,
> >    "time" integer,
> >    bytes integer NOT NULL,
> >    path_id integer,
> >    protocol public.protocol_enum
> > );
> >
> > Partitions:
> > create table url_hits_2011_12 (
> >   check (
> >          "time" >= extract ('epoch' from timestamp '2011-12-01
> > 00:00:00')::int4
> >          and "time" <= extract ('epoch' from timestamp '2011-12-31
> > 23:59:59')::int4
> >   )
> > ) INHERITS (url_hits);
> >
> >
> > CREATE RULE url_hits_2011_12_insert as
> > ON INSERT TO url_hits
> > where
> >   ( "time" >= extract ('epoch' from timestamp '2011-12-01
> > 00:00:00')::int4 and "time" <= extract ('epoch' from timestamp
> > '2011-12-31
> > 23:59:59')::int4 )
> > DO INSTEAD
> >  INSERT INTO  url_hits_2011_12 VALUES (NEW.*) ;
> >
> > ...
> >
> > create table url_hits_2009_08 (
> >   check (
> >          "time" >= extract ('epoch' from timestamp '2009-08-01
> > 00:00:00')::int4
> >          and "time" <= extract ('epoch' from timestamp '2009-08-31
> > 23:59:59')::int4
> >   )
> > ) INHERITS (url_hits);
> >
> >
> > CREATE RULE url_hits_2009_08_insert as
> > ON INSERT TO url_hits
> > where
> >   ( "time" >= extract ('epoch' from timestamp '2009-08-01
> > 00:00:00')::int4 and "time" <= extract ('epoch' from timestamp
> > '2009-08-31
> > 23:59:59')::int4 )
> > DO INSTEAD
> >  INSERT INTO  url_hits_2009_08 VALUES (NEW.*) ;
> >
> > ...
> >
> > the explain plan shows most any query scans/hits all partitions even if
> > we specify the partition key:
> >
> > explain select * from pwreport.url_hits where "time" >
> > date_part('epoch'::text, '2009-08-12'::timestamp without time
> > zone)::integer;
>
> Have you tried using extract here instead of date_part ?

Yes, same results:

explain select * from pwreport.url_hits where "time" > extract('epoch' from
timestamp '2009-08-12 00:00:00')::int4;
                                             QUERY PLAN
------------------------------------------------------------------------------------------------------
 Result  (cost=0.00..23785180.16 rows=817269615 width=432)
  ->  Append  (cost=0.00..23785180.16 rows=817269615 width=432)

        ->  Seq Scan on url_hits  (cost=0.00..12.12 rows=57 width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_12 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_11 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_10 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_09 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_08 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_07 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_06 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_05 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_04 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_03 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_02 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2011_01 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_12 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_11 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_10 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_09 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_08 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_07 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_06 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_05 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_04 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_03 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_02 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2010_01 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2009_12 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2009_11 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2009_10 url_hits  (cost=0.00..12.12 rows=57
width=432)
              Filter: ("time" > 1250035200)

        ->  Seq Scan on url_hits_2009_09 url_hits  (cost=0.00..1856896.86
rows=76384671 width=128)

              Filter: ("time" > 1250035200)
        ->  Seq Scan on url_hits_2009_08 url_hits  (cost=0.00..21927943.80
rows=740883348 width=131)
              Filter: ("time" > 1250035200)
(62 rows)

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