Message-ID: <54C446F7.9050504@2ndquadrant.com>
Date: Sun, 25 Jan 2015 02:29:27 +0100
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Organization: 2ndQuadrant
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To: pgsql-performance@postgresql.org
Subject: Re: Initial insert
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Hi,

On 22.1.2015 17:46, Laurent Cathala wrote:
> Hi, 
> I'm trying to create datas on an initial import and i'm encountering a
> performance issue.
> I've 2 tables, my process create a record in each table and execute a
> sum with join on this 2 tables. (and other requests but there are very fast)
> 
> My 2 tables are empty before the import.
> 
> My count query is :
> select sum(quantitest0_.quantite_valeur) as col_0_0_ from
> dm5_quantitestock quantitest0_, dm5_caracteristiquearticlestock
> caracteris1_ where
> quantitest0_.id_caracteristiquearticlestock=caracteris1_.id and
> caracteris1_.id_article='4028804c4a311178014a346546967c59'
> 
> i use parameterized request.
> 
> My process create only 6000 records in each table.
> 
> During the whole process this sum request lasts longer and longer.
> 
> The auto-explain plan show an seq scan 
> 
> ----------
>   Query Text: select sum(quantitest0_.quantite_valeur) as col_0_0_ from
> dm5_quantitestock quantitest0_, dm5_caracteristiquearticlestock
> caracteris1_ where
> quantitest0_.id_caracteristiquearticlestock=caracteris1_.id and
> caracteris1_.id_article=$1
>         Aggregate  (cost=2.04..2.05 rows=1 width=26) (actual
> time=862.621..862.621 rows=1 loops=1)
>           Output: sum(quantitest0_.quantite_valeur)
>           ->  Nested Loop  (cost=0.00..2.04 rows=1 width=26) (actual
> time=862.618..862.618 rows=0 loops=1)
>                 Output: quantitest0_.quantite_valeur
>                 Join Filter:
> ((quantitest0_.id_caracteristiquearticlestock)::text =
> (caracteris1_.id)::text)
>                 Rows Removed by Join Filter: 1869
>                 ->  Seq Scan on public.dm5_quantitestock quantitest0_
>  (cost=0.00..1.01 rows=1 width=164) (actual time=0.004..0.408 rows=1869
> loops=1)
>                       Output: quantitest0_.id,
> quantitest0_.datefinvalidite, quantitest0_.quantite_valeur,
> quantitest0_.id_caracteristiquearticlestock,
> quantitest0_.id_caracteristiquelieustock,
> quantitest0_.datecreationsysteme, quantitest0_.datemodificationsysteme,
> quantitest0_.id_creeparsysteme, quantitest0_.id_modifieparsysteme
>                 ->  Seq Scan on public.dm5_caracteristiquearticlestock
> caracteris1_  (cost=0.00..1.01 rows=1 width=42) (actual
> time=0.456..0.456 rows=1 loops=1869)
>                       Output: caracteris1_.id,
> caracteris1_.datefinvalidite, caracteris1_.id_lot,
> caracteris1_.id_article, caracteris1_.id_numeroserie,
> caracteris1_.datecreationsysteme, caracteris1_.datemodificationsysteme,
> caracteris1_.id_modifieparsysteme, caracteris1_.id_creeparsysteme
>                       Filter: ((caracteris1_.id_article)::text = ($1)::text)
>                       Rows Removed by Filter: 1869
> -----------
> 
> if a launch an analyse during the process, the explain use index, but
> the time remains the same.
> 
> ---------
> Query Text: select sum(quantitest0_.quantite_valeur) as col_0_0_ from
> dm5_quantitestock quantitest0_, dm5_caracteristiquearticlestock
> caracteris1_ where
> quantitest0_.id_caracteristiquearticlestock=caracteris1_.id and
> caracteris1_.id_article=$1
> Aggregate  (cost=16.55..16.56 rows=1 width=26) (actual
> time=654.998..654.998 rows=1 loops=1)
>  Output: sum(quantitest0_.quantite_valeur)
>  ->  Nested Loop  (cost=0.00..16.55 rows=1 width=26) (actual
> time=654.994..654.994 rows=0 loops=1)
>        Output: quantitest0_.quantite_valeur
>        Join Filter: ((quantitest0_.id_caracteristiquearticlestock)::text
> = (caracteris1_.id)::text)
>        Rows Removed by Join Filter: 1651
>        ->  Index Scan using x_dm5_quantitestock_00 on
> public.dm5_quantitestock quantitest0_  (cost=0.00..8.27 rows=1
> width=164) (actual time=0.011..0.579 rows=1651 loops=1)
>              Output: quantitest0_.id, quantitest0_.datefinvalidite,
> quantitest0_.quantite_valeur,
> quantitest0_.id_caracteristiquearticlestock,
> quantitest0_.id_caracteristiquelieustock,
> quantitest0_.datecreationsysteme, quantitest0_.datemodificationsysteme,
> quantitest0_.id_creeparsysteme, quantitest0_.id_modifieparsysteme
>        ->  Index Scan using dm5_caracteristiquearticlestock_pkey on
> public.dm5_caracteristiquearticlestock caracteris1_  (cost=0.00..8.27
> rows=1 width=42) (actual time=0.395..0.395 rows=1 loops=1651)
>              Output: caracteris1_.id, caracteris1_.datefinvalidite,
> caracteris1_.id_lot, caracteris1_.id_article,
> caracteris1_.id_numeroserie, caracteris1_.datecreationsysteme,
> caracteris1_.datemodificationsysteme, caracteris1_.id_modifieparsysteme,
> caracteris1_.id_creeparsysteme
>              Filter: ((caracteris1_.id_article)::text =
> '4028804c4a311178014a346547307cce'::text)
>              Rows Removed by Filter: 1651
> 
> ----------

Why is the first query using a parameter ($1) while the second one uses
a string literal? Have you executed them differently?

> 
> If i create the first 1000 records, commit and end transaction, the 
> whole import is very fast.

And what plans do the queries use?

> 
> I can't change my process to cut the process in little part...

We're talking about a 600-800 ms query - even if you cut it to 1 ms, I
don't see how this would do a difference in a batch-style job.

If you're doing many such queries (with different id_article values),
you may do something like this

select caracteris1_.id_article, sum(quantitest0_.quantite_valeur) as
col_0_0_ from dm5_quantitestock quantitest0_,
dm5_caracteristiquearticlestock caracteris1_ where
quantitest0_.id_caracteristiquearticlestock=caracteris1_.id
group by caracteris1_.id_article

and then query this (supposedly much smaller) table.

regards

-- 
Tomas Vondra                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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