Re: Append Cost in query planners - Mailing list pgsql-performance

Nimesh Satam wrote:
> Heikki,
>
>
> Thanks for your reply. Will try to do the changes and rivert back. I had one
> more requirement for partitioning.
>
> I wanted to inherit two different tables for partition. Below is the query
> used to create the table, an crete the inheritance.
>
>
> CREATE TABLE metrics_d20070601 (CHECK (sqldate = '20070601')) INHERITS
> (metrics, date);
>
> Further more we are using the below mentioned query:
>
> SELECT rs.id AS sid, rs.name AS sname, rc.id AS cid, rc.name AS cname,
> rc.type AS rtype, rc.act_type AS acttype, ra.id AS adid, ra.name AS avname,
> rch.id AS chid, rch.name AS chname, rcr.dim AS dim, SUM(metrics.imp_del) AS
> imp, SUM(metrics.clidel) AS cli, date.sqldate AS date, rg.id AS gid
> FROM metrics, rn CROSS JOIN date, ra, rs, rc, rch, rcr, rg
> WHERE metrics.netkey = rn.key
> AND rn.id = 10
> AND metrics.advkey = ra.key
> AND metrics.campkey = rc.key
> AND metrics.skey = rs.key
> AND metrics.chkey = rch.key
> AND metrics.cr_key = rcr.key
> AND date.sqldate BETWEEN '6/01/2007' AND '6/01/2007'
> AND metrics.gkey = rg.key
> GROUP BY date.sqldate, rs.id, rs.name, ra.id, ra.name, rc.id, rc.name,
> rc.rev_type, rc.act_type, rch.id, rch.name, rcr.dim, rg.id;
>
> And the query execution plan is as below
>
>
> QUERY
> PLAN
>
>
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>  GroupAggregate  (cost=589766.28..651315.41 rows=1119075 width=127)
>    ->  Sort  (cost=589766.28..592563.97 rows=1119075 width=127)
>          Sort Key: public.date.sqldate, rs.id, rs.name, ra.id, ra.name,
> rc.id, rc.name, rc.rtype, rc.act_type, rch.id, rch.name, rcr.dim, rg.id
>          ->  Hash Join  (cost=64914.87..433619.51 rows=1119075 width=127)
>                Hash Cond: ("outer".adv_key = "inner"."key")
>                ->  Hash Join  (cost=64419.08..402349.16 rows=1119075
> width=111)
>                      Hash Cond: ("outer".s_key = "inner"."key")
>                      ->  Hash Join  (cost=63827.54..368185.38 rows=1119075
> width=96)
>                            Hash Cond: ("outer".campkey = "inner"."key")
>                            ->  Hash Join
> (cost=61339.00..323731.53rows=1119075 width=66)
>                                  Hash Cond: ("outer".chkey = "inner"."key")
>                                  ->  Hash Join
> (cost=59480.62..293896.26rows=1119075 width=46)
>                                        Hash Cond: ("outer".cr_key =
> "inner"."key")
>                                        ->  Hash Join  (cost=
> 51298.73..243749.06 rows=1119075 width=48)
>                                              Hash Cond: ("outer".gkey =
> "inner"."key")
>                                              ->  Hash Join  (cost=
> 51051.50..204334.21 rows=1119075 width=48)
>                                                    Hash Cond:
> (("outer".netkey = "inner"."key") AND ("outer".date_key = "inner"."key"))
>                                                    ->  Append  (cost=
> 0.00..51795.56 rows=1901256 width=48)
>                                                          ->  Seq Scan on
> metrics  (cost=0.00..25614.71 rows=940271 width=48)
>                                                          ->  Seq Scan on
> metrics_d20070601 metrics  (cost=0.00..26180.85 rows=960985 width=48)
>                                                    ->  Hash  (cost=
> 40615.57..40615.57 rows=960986 width=16)
>                                                          ->  Nested Loop
> (cost=0.00..40615.57 rows=960986 width=16)
>                                                                ->  Index
> Scan using rpt_netw_key_idx on rn  (cost=0.00..16.92 rows=1 width=4)
>                                                                      Filter:
> (id = 10)
>                                                                ->  Append
> (cost=0.00..30988.79 rows=960986 width=12)
>                                                                      ->
> Index Scan using rpt_dt_sqldt_idx on date  (cost=0.00..3.02 rows=1 width=12)
>
> Index Cond: ((sqldate >= '2007-06-01 00:00:00'::timestamp without time zone)
> AND (sqldate <= '2007-06-01 00:00:00'::timestamp without time zone))
>                                                                      ->  Seq
> Scan on metrics_d20070601 rpt_date  (cost=0.00..30985.78 rows=960985
> width=12)
>
> Filter: ((sqldate >= '2007-06-01 00:00:00'::timestamp without time zone) AND
> (sqldate <= '2007-06-01 00:00:00'::timestamp without time zone))
>                                              ->  Hash
> (cost=223.18..223.18rows=9618 width=8)
>                                                    ->  Seq Scan on rg
> (cost=0.00..223.18 rows=9618 width=8)
>                                        ->  Hash
> (cost=7367.71..7367.71rows=325671 width=6)
>                                              ->  Seq Scan on rc  (cost=
> 0.00..7367.71 rows=325671 width=6)
>                                  ->  Hash  (cost=1652.51..1652.51 rows=82351
> width=28)
>                                        ->  Seq Scan on rch  (cost=
> 0.00..1652.51 rows=82351 width=28)
>                            ->  Hash  (cost=2283.83..2283.83 rows=81883
> width=38)
>                                  ->  Seq Scan on rc
> (cost=0.00..2283.83rows=81883 width=38)
>                      ->  Hash  (cost=520.63..520.63 rows=28363 width=23)
>                            ->  Seq Scan on rs  (cost=0.00..520.63 rows=28363
> width=23)
>                ->  Hash  (cost=435.63..435.63 rows=24063 width=24)
>                      ->  Seq Scan on radv  (cost=0.00..435.63 rows=24063
> width=24)
> (41 rows)
>
> Can you let me know how we can avoid the double looping on the metrics
> table. This been a big table causes the queries to slowdown.

Well, if the index on metrics.netkey helps, it doesn't matter if it's
scanned twice.

On a query with that many tables involved, you should try raising
join_collapse_limit from the default. That query accesses 9 tables,
which is just above the default join_collapse_limit of 8, so the planner
is not considering all possible join orders.

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com