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Re: Same query doing slow then quick

From: FFW_Rude <FFW_Rude(at)hotmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Same query doing slow then quick
Date: 2012-09-26 13:36:45
Message-ID: SNT111-W18646B5C50D8B2D96AE68DE19C0@phx.gbl (view raw or whole thread)
Lists: pgsql-performance
Thank you for your answer.
It was already at 16MB and i upped it just this morning to 64MB. Still no change

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Date: Wed, 26 Sep 2012 06:22:35 -0700
From: ml-node+s1045698n5725493h43(at)n5(dot)nabble(dot)com
To: FFW_Rude(at)hotmail(dot)com
Subject: Re: Same query doing slow then quick

	On 09/26/2012 15:03, FFW_Rude wrote:

> Here is the answer to Ray Stell who send me the wiki page of Slow Query. I

> hope i detailed all you wanted (i basicly pasted the page and add my

> answers).


> Full Table and Index Schema:


> schema tables_adresses

> "Tables"

> tables_adresses.adresses_XX (id (serial), X(Double precision),Y (Double

> precision)).

> "Indexes"

> adresses_XX_pkey (Primary key, btree)

> calcul_XX (non unique, Btree on X,Y)


> schema tables_gps

> "Tables"

> tables_gps.gps_XX (id (int),x_max(numeric(10,5)), y_max

> (numeric(10,5)),x_min(numeric(10,5)),y_min(numeric(10,5)))

> "Indexes"

> calculs_XX (non unique Btree x_min,x_max,y_min,y_max)

> gps_10_pkey (Primary key on id btree)


> Approximate rows 250000.

> No large objects in it (just data)


> receives a large number of UPDATEs or DELETEs regularly

> is growing daily


> I can't post an EXPLAIN ANALYZE because of the 6hour query time.


> Postgres version: 9.1


> History: was this query always slow, : "YES"


> Hardware: Ubuntu server last version 32bits


> Daily VACUUM FULL ANALYZE, REINDEX TABLE on all the tables.


> WAL Configuration: Whats a WAL ?


> GUC Settings: i didn't change anything. All is standard.


> shared_buffers should be 10% to 25% of available RAM (it's on 24MB and can't

> go higher. The server has 4Gb)


> effective_cache_size should be 75% of available RAM =>  I don't now what this

> is.
before looking further, please configure shared_buffers and 

effective_cache_size properly, it's fundamental

you'll probably need to raise SHMALL/SHMMAX, take a look at:
for 4GB of RAM I start with shared_buffers to 512MB and 

effective_cache_size to 2GB

> Test changing work_mem: increase it to 8MB, 32MB, 256MB, 1GB. Does it make a

> difference? "No"

default work_mem is very small, set it to something like 16MB




> --

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