Re: Initial insert

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