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Re: function executes sql 100 times longer it should

From: Julius Tuskenis <julius(at)nsoft(dot)lt>
To:
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: function executes sql 100 times longer it should
Date: 2008-11-13 13:29:09
Message-ID: 491C2BA5.7080401@nsoft.lt (view raw or flat)
Thread:
Lists: pgsql-admin
Thank you Vyacheslav.

your "bit or street magic" worked and now I have Execution Plans for both queries:  from function and simple SQL. 
I'm not good in reading and interpreting these please advice witch part should I put my attention to? 


FUNCTION:

"Unique  (cost=290.13..290.15 rows=1 width=132) (actual time=1834.211..1834.222 rows=2 loops=1)"
"  ->  Sort  (cost=290.13..290.14 rows=1 width=132) (actual time=1834.207..1834.209 rows=2 loops=1)"
"        Sort Key: filter_b_preke_matoma.prek_pavadinimas, filter_b_preke_matoma.prek_id, b_kainorascio_sudetis.ks_kaina, b_mato_vienetai.mvnt_trumpinys"
"        Sort Method:  quicksort  Memory: 17kB"
"        ->  Nested Loop Left Join  (cost=1.03..290.12 rows=1 width=132) (actual time=374.851..1834.169 rows=2 loops=1)"
"              Join Filter: (b_grupes_prekes.gp_grupe = b_grupe.grup_id)"
"              Filter: ((b_grupe.grup_id = $1) OR ($1 IS NULL))"
"              ->  Nested Loop Left Join  (cost=1.03..288.07 rows=1 width=136) (actual time=45.915..1795.235 rows=694 loops=1)"
"                    ->  Nested Loop  (cost=1.03..281.39 rows=1 width=132) (actual time=45.902..1789.018 rows=694 loops=1)"
"                          ->  Nested Loop  (cost=1.03..281.11 rows=1 width=140) (actual time=8.021..1734.222 rows=6367 loops=1)"
"                                ->  Nested Loop  (cost=1.03..280.58 rows=1 width=136) (actual time=6.618..79.367 rows=6000 loops=1)"
"                                      ->  Nested Loop  (cost=1.03..268.87 rows=1 width=125) (actual time=6.595..34.114 rows=2820 loops=1)"
"                                            Join Filter: (filter_b_preke_matoma.prek_matovnt = b_mato_vienetai.mvnt_id)"
"                                            ->  Function Scan on filter_b_preke_matoma  (cost=0.00..267.50 rows=5 width=126) (actual time=6.580..11.766 rows=2820 loops=1)"
"                                                  Filter: (((prek_pavadinimas)::text ~~* (('%'::text || ($3)::text) || '%'::text)) OR ($3 IS NULL))"
"                                            ->  Materialize  (cost=1.03..1.06 rows=3 width=7) (actual time=0.001..0.002 rows=3 loops=2820)"
"                                                  ->  Seq Scan on b_mato_vienetai  (cost=0.00..1.03 rows=3 width=7) (actual time=0.005..0.009 rows=3 loops=1)"
"                                      ->  Index Scan using idx_ks_preke on b_kainorascio_sudetis  (cost=0.00..11.67 rows=3 width=15) (actual time=0.007..0.010 rows=2 loops=2820)"
"                                            Index Cond: (b_kainorascio_sudetis.ks_preke = filter_b_preke_matoma.prek_id)"
"                                ->  Index Scan using idx_kag_kainorastis on b_kainorascio_grafikas  (cost=0.00..0.52 rows=1 width=4) (actual time=0.199..0.272 rows=1 loops=6000)"
"                                      Index Cond: (b_kainorascio_grafikas.kag_kainorastis = b_kainorascio_sudetis.ks_kainorastis)"
"                                      Filter: fnk_grafikas_galioja(b_kainorascio_grafikas.kag_grafikas)"
"                          ->  Index Scan using unq_kainorastis_pardavimo_taskui on b_pardavimo_tasko_kainorastis  (cost=0.00..0.28 rows=1 width=4) (actual time=0.005..0.006 rows=0 loops=6367)"
"                                Index Cond: ((b_pardavimo_tasko_kainorastis.ptk_pardavimotaskas = $2) AND (b_pardavimo_tasko_kainorastis.ptk_kainorastis = b_kainorascio_sudetis.ks_kainorastis))"
"                    ->  Index Scan using idx_gp_preke on b_grupes_prekes  (cost=0.00..6.67 rows=1 width=8) (actual time=0.006..0.006 rows=0 loops=694)"
"                          Index Cond: (b_grupes_prekes.gp_preke = filter_b_preke_matoma.prek_id)"
"              ->  Seq Scan on b_grupe  (cost=0.00..1.42 rows=42 width=4) (actual time=0.004..0.023 rows=42 loops=694)"
"Total runtime: 1834.686 ms"


SIMPLE SQL:
"Unique  (cost=281.91..281.93 rows=1 width=132) (actual time=34.438..34.447 rows=2 loops=1)"
"  ->  Sort  (cost=281.91..281.92 rows=1 width=132) (actual time=34.435..34.436 rows=2 loops=1)"
"        Sort Key: filter_b_preke_matoma.prek_pavadinimas, filter_b_preke_matoma.prek_id, b_kainorascio_sudetis.ks_kaina, b_mato_vienetai.mvnt_trumpinys"
"        Sort Method:  quicksort  Memory: 17kB"
"        ->  Nested Loop  (cost=1.07..281.90 rows=1 width=132) (actual time=15.226..34.396 rows=2 loops=1)"
"              ->  Nested Loop  (cost=1.07..280.37 rows=1 width=136) (actual time=15.197..34.331 rows=2 loops=1)"
"                    ->  Nested Loop  (cost=1.07..280.08 rows=1 width=144) (actual time=13.976..34.233 rows=7 loops=1)"
"                          ->  Nested Loop  (cost=1.07..279.55 rows=1 width=140) (actual time=12.178..29.760 rows=7 loops=1)"
"                                ->  Nested Loop  (cost=1.07..269.69 rows=1 width=133) (actual time=12.165..29.700 rows=2 loops=1)"
"                                      ->  Hash Join  (cost=1.07..264.97 rows=15 width=125) (actual time=6.452..13.617 rows=2820 loops=1)"
"                                            Hash Cond: (filter_b_preke_matoma.prek_matovnt = b_mato_vienetai.mvnt_id)"
"                                            ->  Function Scan on filter_b_preke_matoma  (cost=0.00..260.00 rows=1000 width=126) (actual time=6.418..7.828 rows=2820 loops=1)"
"                                            ->  Hash  (cost=1.03..1.03 rows=3 width=7) (actual time=0.013..0.013 rows=3 loops=1)"
"                                                  ->  Seq Scan on b_mato_vienetai  (cost=0.00..1.03 rows=3 width=7) (actual time=0.005..0.007 rows=3 loops=1)"
"                                      ->  Index Scan using idx_gp_preke on b_grupes_prekes  (cost=0.00..0.30 rows=1 width=8) (actual time=0.004..0.004 rows=0 loops=2820)"
"                                            Index Cond: (b_grupes_prekes.gp_preke = filter_b_preke_matoma.prek_id)"
"                                            Filter: (b_grupes_prekes.gp_grupe = 43)"
"                                ->  Index Scan using idx_ks_preke on b_kainorascio_sudetis  (cost=0.00..9.82 rows=3 width=15) (actual time=0.009..0.019 rows=4 loops=2)"
"                                      Index Cond: (b_kainorascio_sudetis.ks_preke = filter_b_preke_matoma.prek_id)"
"                          ->  Index Scan using idx_kag_kainorastis on b_kainorascio_grafikas  (cost=0.00..0.52 rows=1 width=4) (actual time=0.536..0.634 rows=1 loops=7)"
"                                Index Cond: (b_kainorascio_grafikas.kag_kainorastis = b_kainorascio_sudetis.ks_kainorastis)"
"                                Filter: fnk_grafikas_galioja(b_kainorascio_grafikas.kag_grafikas)"
"                    ->  Index Scan using unq_kainorastis_pardavimo_taskui on b_pardavimo_tasko_kainorastis  (cost=0.00..0.28 rows=1 width=4) (actual time=0.009..0.009 rows=0 loops=7)"
"                          Index Cond: ((b_pardavimo_tasko_kainorastis.ptk_pardavimotaskas = 18) AND (b_pardavimo_tasko_kainorastis.ptk_kainorastis = b_kainorascio_sudetis.ks_kainorastis))"
"              ->  Seq Scan on b_grupe  (cost=0.00..1.52 rows=1 width=4) (actual time=0.012..0.020 rows=1 loops=2)"
"                    Filter: (b_grupe.grup_id = 43)"
"Total runtime: 34.804 ms"


Vyacheslav Kalinin rašė:

> Most likely, you get different plans because the function has to deal with the parametrized query, hence planner cannot effectively use statistics. For example conditions like this
> WHERE (grup_id=$2 OR $2 is Null)
> would prevent planner from use of index (if there is one), while with literal query they would be simplified to just
> WHERE grup_id=42.
>   
> On Thu, Nov 13, 2008 at 11:16 AM, Julius Tuskenis <julius(at)nsoft(dot)lt <mailto:julius(at)nsoft(dot)lt>> wrote:
>
>     Its a good start, but leads to nothing because Explain doesn't go into the function.
>
> It does, after a bit of street magic:
> CREATE OR REPLACE FUNCTION fnk_grupes_prekes(prm_
> pardavimo_taskas integer, prm_grupe integer, prm_filtras character varying)
>  RETURNS refcursor AS
> $BODY$
> declare
> cur refcursor;
> begin
> open cur for
> explain analyze
> SELECT DISTINCT prek_id, prek_pavadinimas, ks_kaina, mvnt_trumpinys
> FROM  filter_b_preke_matoma()
> LEFT OUTER JOIN b_grupes_prekes ON (gp_preke=prek_id)
> LEFT OUTER JOIN b_grupe ON (gp_grupe=grup_id)
> JOIN b_mato_vienetai ON (mvnt_id=prek_matovnt)
> JOIN b_kainorascio_sudetis ON (ks_preke = prek_id)
> JOIN b_kainorascio_grafikas ON (ks_kainorastis=kag_kainorastis)
> JOIN b_pardavimo_tasko_kainorastis ON (ks_kainorastis=ptk_kainorastis)
> WHERE (grup_id=$2 OR $2 is Null)
>  AND ptk_pardavimotaskas=$1
>  AND ((prek_pavadinimas ILIKE ('%'||$3||'%')) OR $3 is NULL)
>  AND fnk_grafikas_galioja(kag_grafikas) = true
> ORDER BY prek_pavadinimas;
> return cur;
> end;
> $BODY$
>  LANGUAGE 'plpgsql' VOLATILE;
> begin;
> select fnk_grupes_prekes(...);
> fetch all in cur;
> (I didnt test the above commands, but that's what I do to debug in-function plans)
>   
>   
>   

-- 
Julius Tuskenis
Programavimo skyriaus vadovas
UAB nSoft
mob. +37068233050


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