From: Rod Taylor <rbt@rbt.ca>
To: Ivan Voras <ivoras@fer.hr>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <450FEF1A.4070106@fer.hr>
References: <450FEF1A.4070106@fer.hr>
Date: Tue, 19 Sep 2006 09:53:07 -0400
Message-Id: <1158673987.71040.24.camel@home>
Mime-Version: 1.0
Subject: Re: Optimizing DELETE
Content-Type: text/plain
Content-Transfer-Encoding: 7bit

On Tue, 2006-09-19 at 15:22 +0200, Ivan Voras wrote:
> I've just fired off a "DELETE FROM table" command (i.e. unfiltered 
> DELETE) on a trivially small table but with many foreign key references 
> (on similar-sized tables), and I'm waiting for it to finish. It's been 
> 10 minutes now, which seems very excessive for a table of 9000 rows on a 
> 3 GHz desktop machine.

I would guess that a few of those referenced tables are missing indexes
on the referenced column.

> 'top' says it's all spent in USER time, and there's a ~~500KB/s write 
> rate going on. Just before this DELETE, I've deleted data from a larger 
> table (50000 rows) using the same method and it finished in couple of 
> seconds - maybe it's a PostgreSQL bug?
> 
> My question is: assuming it's not a bug, how to optimize DELETEs? 
> Increasing work_mem maybe?
> 
> (I'm using PostgreSQL 8.1.4 on FreeBSD 6- amd64)
> 
> (I know about TRUNCATE; I need those foreign key references to cascade)
> 
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