From: "Carlo Stonebanks" <stonec.register@sympatico.ca>
Subject: Re: REPOST: Nested loops row estimates always too high
Date: Mon, 24 Sep 2007 14:12:01 -0400
Organization: Hub.Org Networking Services
Lines: 40
Message-ID: <fd8ukj$s38$1@news.hub.org>
References: <fcu215$2em3$1@news.hub.org>
	<1190616376.17050.51.camel@neuromancer.home.net>
Mime-Version: 1.0
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original
Content-Transfer-Encoding: 7bit
In-Reply-To: <1190616376.17050.51.camel@neuromancer.home.net>
To: pgsql-performance@postgresql.org

Has anyone offered any answers to you? No one else has replied to this post.


"Ow Mun Heng" <Ow.Mun.Heng@wdc.com> wrote in message 
news:1190616376.17050.51.camel@neuromancer.home.net...
> On Thu, 2007-09-20 at 11:02 -0400, Carlo Stonebanks wrote:
>> (SORRY FOR THE REPOST, I DON'T SEE MY ORIGINAL QUESTION OR ANY ANSWERS 
>> HERE)
>>
>> I am noticing that my queries are spending a lot of time in nested loops.
>> The table/index row estimates are not bad, but the nested loops can be 
>> off
>> by a factor of 50. In any case, they are always too high.
>>
>> Are the over-estimations below significant, and if so, is this an 
>> indication
>> of a general configuration problem?
> Sounds much like the issue I was seeing as well.
>
>>
>> Unique  (cost=67605.91..67653.18 rows=4727 width=16) (actual
>> time=8634.618..8637.918 rows=907 loops=1)
>
> You can to rewrite the queries to individual queries to see it if helps.
>
> In my case, I was doing
>
> select a.a,b.b,c.c from
> (select a from x where) a <--- Put as a SRF
> left join (
> select b from y where ) b <--- Put as a SRF
> on a.a = b.a
>
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>