To: "Thomas Mueller" <news-exp-jul05@tmueller.com>,
	pgsql-sql@postgresql.org
Subject: Re: Simple delete takes hours
References: <d0807h$vuu$1@sea.gmane.org>
Message-ID: <opsm4zaaizth1vuj@musicbox>
Date: Sat, 05 Mar 2005 00:24:00 +0100
From: PFC <lists@boutiquenumerique.com>
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	Every time a row is removed from pwd_name, the ON DELETE CASCADE trigger  
will look in pwd_name_rev if there is a row to delete... Does it have an  
index on pwd_name_rev( rev_of ) ? If not you'll get a full table scan for  
every row deleted in pwd_name...


On Thu, 03 Mar 2005 22:44:58 +0100, Thomas Mueller  
<news-exp-jul05@tmueller.com> wrote:

> Hi there,
>
> I have a simple database:
>
> CREATE TABLE pwd_description (
>    id SERIAL                NOT NULL UNIQUE PRIMARY KEY,
>    name varchar(50)         NOT NULL
> );
>
> CREATE TABLE pwd_name (
>    id SERIAL                NOT NULL UNIQUE PRIMARY KEY,
>    description integer      NOT NULL REFERENCES pwd_description(id),
>    name varchar(50)         NOT NULL,
>    added timestamp          DEFAULT now()
> );
>
> CREATE TABLE pwd_name_rev (
>    id SERIAL                NOT NULL UNIQUE PRIMARY KEY,
>    description integer      NOT NULL REFERENCES pwd_description(id),
>    rev_of integer           NOT NULL REFERENCES pwd_name(id) ON DELETE  
> CASCADE,
>    name varchar(50)         NOT NULL
> );
>
> The indexes shouldn't matter I think.
>
> pwd_name_rev is filled by a stored procedure and a trigger (ON INSERT)  
> when something is inserted to pwd_name. Both tables contain about  
> 4.500.000 emtries each.
>
> I stopped 'delete from pwd_name where description=1' after about 8 hours  
> (!). The query should delete about 500.000 records.
> Then I tried 'delete from pwd_name_rev where description=1' - this took  
> 23 seconds (!).
> Then I retried the delete on pwd_name but it's running for 6 hours now.
>
> I use PostgreSQL 7.4.7 on Linux 2.6.10. The machine is a Celeron 2 GHz  
> with 512 MB RAM.
>
> PostgreSQL should do a full table scan I think, get all records with  
> description=1 and remove them - I don't understand what's happening for  
>  >8 hours.
>
>
> Any help is appreciated.
>
>
> Thomas
>
>
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